Anatomy & Physiology

Glossary

476 terms so far. Each one links to the page that teaches it.

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abdominal quadrants: The four areas made by a midsagittal line and a transverse line crossing at the navel: right upper, left upper, right lower and left lower, named for the patient's own sides. quadrans (Latin) a fourth part Taught in Body regions and abdominal quadrants.
abdominopelvic cavity (ab-DOM-ih-noh-PEL-vik): The part of the ventral body cavity below the diaphragm: the abdominal cavity above and the pelvic cavity below, with only an imaginary boundary between them. abdomin/o abdomen · pelv/i basin, pelvis Taught in Body cavities and serous membranes.
abdominopelvic regions (hy-poh-KON-dree-ak, ep-ih-GAS-trik): The nine areas made by two vertical and two horizontal lines across the abdomen: right and left hypochondriac with the epigastric between them, right and left lumbar with the umbilical between them, and right and left iliac with the hypogastric between them. hypo- below · chondr/o cartilage · epi- upon, over · gastr/o stomach · umbilicus (Latin) navel Taught in Body regions and abdominal quadrants.
absolute and relative refractory periods: The absolute refractory period is the time, about 1 ms from threshold through most of the falling phase, when no stimulus can start another action potential. The relative refractory period follows it, when only a stronger-than-normal stimulus can. refractarius stubborn (Latin) · absolutus complete (Latin) Taught in The action potential in detail.
acid: A substance that releases hydrogen ions (H+) when it dissolves in water, raising the H+ concentration. A strong acid releases nearly all of them; a weak acid releases only a small share. acid- sour Taught in Acids, bases, pH and buffers.
acidosis and alkalosis (definitions) (as-ih-DOE-sis; al-kuh-LOE-sis): Acidemia is blood pH below 7.35 and alkalemia is blood pH above 7.45. Acidosis and alkalosis are the processes that push pH down or up; in everyday speech the words are often used for the blood state itself. -osis condition, process · -emia blood condition Taught in Acids, bases, pH and buffers.
action potential: A rapid, all-or-none reversal of the membrane potential: sodium rushes in (to about +30 mV), then potassium flows out, returning the membrane to rest. It travels along the membrane without shrinking; in a neuron it is also called a nerve impulse. Taught in Electrical signals: graded potentials and action potentials.
active transport: Movement of a substance across a membrane that requires the cell to supply energy, usually from ATP. It usually moves the substance against its gradient; vesicle transport also counts. activus doing, acting Taught in Active transport and vesicles.
ADH in blood pressure control (vay-zoh-PRESS-in): The role of antidiuretic hormone in blood pressure: it makes the kidneys keep water, and at the high levels a large fall in volume produces, it also constricts arterioles. Its other name, vasopressin, reflects that effect. anti- against · di- through · -uretic relating to urine · vas/o vessel Taught in Long-term blood pressure regulation.
aerobic respiration (air-OH-bik): The complete breakdown of fuel using oxygen: glycolysis, then the citric acid cycle in the mitochondrion, then the electron transport chain in the inner mitochondrial membrane, where oxygen accepts electrons and most ATP is made. aer- air · bio- life · citr- lemon Taught in How cells make ATP.
afferent pathway (AF-er-ent): The route, usually a nerve, that carries information from the sensory receptor toward the control center. af- (ad-) toward · fer to carry Taught in Homeostasis and feedback loops.
afterload: The pressure a ventricle must overcome to open its semilunar valve and eject blood, set mainly by aortic pressure for the left ventricle. A higher afterload leaves more blood in the ventricle after ejection and lowers stroke volume. Taught in Cardiac output and its control.
airway defenses (MYOO-koh-SIL-ee-air-ee): The ways the airway keeps particles and microorganisms out of the alveoli: hairs in the nasal vestibule, sticky mucus with lysozyme, defensins and IgA, the mucociliary escalator (cilia that move the mucus sheet toward the pharynx to be swallowed), and the cough reflex (vagus nerve) and sneeze reflex (trigeminal nerve), which blast irritants out. muc- mucus · cili- eyelash Taught in Nose, pharynx and larynx.
airway resistance (AZ-muh): The opposition to airflow through the airways, which rises steeply as airway radius falls (resistance depends on 1 ÷ r⁴). Bronchoconstriction (smooth muscle contraction, from acetylcholine, histamine or leukotrienes) raises it; bronchodilation (relaxation, from epinephrine on beta-2 receptor proteins) lowers it. Asthma is a chronic inflammatory airway disease in which bronchoconstriction, wall swelling and mucus narrow the airways. bronch- windpipe · con- together · strict- draw tight · dilat- widen · asthma panting Taught in Pulmonary ventilation.
alveolar ventilation (al-VEE-oh-lar): The volume of fresh air that reaches the alveoli each minute: (tidal volume − dead space) × respiratory rate, about 4.2 L/min at rest. Shallow breathing lowers it even when minute ventilation stays the same. alveol- small cavity · -ar pertaining to Taught in Lung volumes and ventilation rates.
alveoli (in detail) (al-VEE-oh-lye): The tiny air sacs, about 0.2 mm across and numbering hundreds of millions, where gases cross between air and blood. They cluster in alveolar sacs. Thin type I alveolar cells form the wall; cuboidal type II cells secrete surfactant, a film that lowers surface tension, and replace type I cells; alveolar macrophages engulf particles; alveolar pores link neighbors. alveol- small cavity Taught in Trachea, bronchial tree, alveoli and lungs.
anaerobic metabolism (AN-air-OH-bik): Making ATP without using oxygen: glycolysis followed by conversion of pyruvate to lactate, which regenerates NAD+ so glycolysis can continue. It yields only 2 ATP per glucose. an- without · aer- air · bio- life · lact- milk Taught in How cells make ATP.
anastomosis (uh-nas-tuh-MOH-sis): A connection between two blood vessels. Where branches of two arteries join, blood can reach tissue by a second route, called collateral circulation. ana- again · stom- mouth Taught in Blood flow through the heart and the two circuits.
anatomical position: The reference posture for describing the body: standing upright and facing forward, feet flat and pointing forward, arms at the sides with the palms facing forward and the thumbs pointing away from the body. Every directional term assumes this posture. Taught in Anatomical position and directional terms.
anatomy (uh-NAT-uh-mee): The study of the body's structures: their shape, size, parts and position. Gross anatomy covers what you can see unaided, microscopic anatomy what needs a microscope, regional anatomy one body part at a time, and systemic anatomy one organ system at a time. ana- apart, up · -tomy cutting Taught in Levels of organization and organ systems.
ANP in blood pressure control (nay-tree-yoo-RET-ik): The role of atrial natriuretic peptide in lowering blood pressure: released when the atria are stretched, it makes the kidneys excrete sodium and water, lowers renin, aldosterone and ADH, and relaxes arterioles. natri- sodium · -uretic relating to urine Taught in Long-term blood pressure regulation.
anterior and posterior: Anterior means toward the front of the body; posterior means toward the back. Ventral (belly side) and dorsal (back side) mean the same in a standing human. ante- before · post- after, behind · venter (Latin) belly · dorsum (Latin) back Taught in Anatomical position and directional terms.
apoptosis (ap-op-TOH-sis): Programmed cell death: an orderly self-destruction in which the cell's own enzymes dismantle it into membrane-wrapped pieces that neighboring cells engulf, without spilling its contents. apo- away · -ptosis falling Taught in Cell division and differentiation.
aquaporin (ak-wuh-POR-in): A membrane protein that forms a water channel, letting water molecules cross in single file far faster than through the bare bilayer. Water still moves in the direction osmosis sets. aqua water · porus passage Taught in Passive transport across membranes.
arrhythmia (uh-RITH-mee-uh; tak-ih-KAR-dee-uh; bray-dee-KAR-dee-uh): Any heart rhythm that is abnormal in rate, regularity, starting point or conduction; also called dysrhythmia. Examples are tachycardia (above 100 per minute at rest), bradycardia (below 60), heart block, atrial fibrillation and ventricular fibrillation, which is treated by defibrillation. An artificial pacemaker fires when the heart's own rate is too slow. a- without · dys- abnormal · tachy- fast · brady- slow · fibrill- small fiber · de- undo Taught in The electrocardiogram.
arteries of the abdomen and pelvis (SEE-lee-ak; mez-en-TAIR-ik; ILL-ee-ak): The branches of the abdominal aorta: three single gut arteries (celiac trunk, superior mesenteric, inferior mesenteric) and paired renal and gonadal arteries, ending in the common iliac arteries, which split into internal iliacs for the pelvis and external iliacs for the legs. The celiac trunk splits into the left gastric artery, the splenic artery and the common hepatic artery. celi- belly · mes- middle · enter- gut · ren- kidney · gon- seed · gastr- stomach · hepat- liver Taught in The major systemic arteries.
arteries of the head and neck (bray-kee-oh-seh-FAL-ik; kuh-ROT-id): The brachiocephalic trunk (right side only), the common carotid arteries, which split into external carotids for the face and scalp and internal carotids for the brain, and the vertebral arteries from the subclavians. The carotid sinus is the pressure-sensing bulge at the start of each internal carotid. brachi- arm · cephal- head · karot- stupor (Greek) · sinus hollow, pocket Taught in The major systemic arteries.
arteries of the limbs (sub-KLAY-vee-un; pop-lih-TEE-ul; dor-SAY-lis PEE-dis): In the arm, one artery renamed at landmarks: subclavian, axillary, brachial, then the radial and ulnar arteries, which join in the palmar arches. In the leg: femoral (with its deep femoral branch), popliteal, then the anterior tibial, which becomes the dorsalis pedis, and the posterior tibial. sub- under · clavi- collarbone · axilla armpit · brachi- arm · poplit- back of the knee · dorsum back, top · ped- foot Taught in The major systemic arteries.
arteriole (ar-TEER-ee-ohl): The smallest artery, under about 0.1 mm across, with one to a few layers of smooth muscle. Arterioles are the main resistance vessels; their steady partial contraction, vascular tone, sets how much blood enters each capillary bed. arteri- artery · -ole small Taught in Structure of blood vessels.
artery, vein and capillary (basic): The three kinds of blood vessel. An artery carries blood away from the heart, a vein carries blood back toward the heart, and a capillary is the thinnest vessel, where materials pass between blood and cells. capillaris (Latin) hairlike Taught in Levels of organization and organ systems.
ascending and descending tracts: The bundles of axons in the spinal cord's white columns. Ascending tracts carry sensory information up to the brain; descending tracts carry motor commands down. Their names give origin then destination, and most cross the midline somewhere along their path. ascend- climb up · descend- climb down · tractus a drawing out Taught in The spinal cord.
atherosclerosis (ATH-er-oh-skleh-ROH-sis): The buildup of plaques of fat, foam cells and fibrous tissue in the tunica intima of large and medium arteries. Plaques narrow the lumen and can rupture, triggering a thrombus that blocks the artery. ather/o gruel, paste · scler/o hard · -osis condition Taught in Hypertension, heart failure and shock.
atomic number, mass number and isotopes (EYE-so-tope): The atomic number is an atom's proton count, which defines the element; the mass number is protons plus neutrons. Isotopes are atoms of one element with different numbers of neutrons, and radioisotopes are isotopes whose unstable nuclei give off radiation. iso- equal · top/o place Taught in Atoms, ions and chemical bonds.
atomic structure: The smallest unit of an element that still behaves like that element: a nucleus of protons and neutrons with electrons arranged in shells around it. a- not · tom/o cut Taught in Atoms, ions and chemical bonds.
ATP (uh-DEN-o-seen try-FOS-fate): Adenosine triphosphate: a nucleotide of adenine, ribose and three phosphate groups. Splitting off the outer phosphate by hydrolysis leaves ADP (adenosine diphosphate) and releases energy that cells use for work. tri- three · di- two Taught in Carbohydrates, lipids, proteins and nucleic acids.
ATP as the energy currency (fos-for-ih-LAY-shun): The splitting of ATP by water into ADP and phosphate, which releases energy because the products are more stable than ATP. An ATPase is an enzyme that does this; phosphorylation is attaching a phosphate group to another molecule, which changes its energy and shape. hydro- water · -lysis splitting · -ase enzyme Taught in Energy, metabolism and enzymes.
atrial reflex (BAYN-bridj): A reflex in which stretch of the atria and nearby large veins, from more venous return, raises heart rate through the cardiovascular center. Also called the Bainbridge reflex. atri- entrance hall Taught in Short-term blood pressure regulation.
atrioventricular node (ay-tree-oh-ven-TRIK-yoo-lur): The atrioventricular node: autorhythmic tissue in the lower interatrial septum, and the only normal electrical doorway from atria to ventricles. It conducts slowly, causing the AV nodal delay of about 0.1 second, during which the atria finish contracting. atrio- atrium · ventricul- ventricle Taught in The conduction system and pacemaker cells.
atrioventricular valves (MY-trul; KOR-dee ten-DIN-ee-ee): The valves between each atrium and its ventricle: the tricuspid valve on the right and the mitral (bicuspid) valve on the left. Chordae tendineae tie their cusps to papillary muscles, which keep the cusps from flipping into the atria when the ventricles contract. tri- three · bi- two · cusp point · chord- string · tendin- tendon · papilla nipple Taught in Heart valves, septa and internal structure.
autonomic nervous system (basic) (aw-toh-NOM-ik): The part of the motor division that controls cardiac muscle, smooth muscle and glands, mostly without conscious control. Its sympathetic division (fight-or-flight) dominates in stress and exercise; its parasympathetic division (rest-and-digest) dominates at rest. auto- self · nom- law · sym- together · path- feeling · para- beside Taught in Organization of the nervous system.
autorhythmic cell (aw-toh-RITH-mik): A specialized cardiac muscle cell, also called a pacemaker cell, that depolarizes to threshold on its own with no outside stimulus. About 1 percent of heart cells are autorhythmic; they start and conduct each heartbeat's signal and contract only weakly. auto- self · rhythm- regular beat · -ic relating to Taught in The conduction system and pacemaker cells.
baroreceptor reflex: The negative feedback loop that corrects fast changes in blood pressure: baroreceptor signals reach the cardiovascular center, which adjusts sympathetic and vagal output to the heart, arterioles and veins. Also called the baroreflex; on standing it is the orthostatic reflex. bar/o pressure, weight · re- back · flex bend Taught in Short-term blood pressure regulation.
baroreceptors (BAIR-oh-ree-SEP-terz): Stretch-sensitive sensory receptors in the walls of the carotid sinuses and the aortic arch (the arch group is sometimes called the aortic sinuses, a name anatomists give to the bulges at the root of the aorta). They fire faster when arterial pressure stretches the wall more, and they reset to a new pressure within a day or two. bar/o pressure, weight Taught in Short-term blood pressure regulation.
basal nuclei (KAW-dayt; pyoo-TAY-men; GLOH-bus PAL-ih-dus): Masses of gray matter deep in the cerebrum (the caudate and putamen, together the striatum, and the globus pallidus), working with the subthalamus and substantia nigra. They help select wanted movements and suppress unwanted ones; the older name is basal ganglia. cauda tail · putamen shell · globus pallidus pale globe · substantia nigra black substance Taught in Regions of the brain.
base (chemistry) (AL-kuh-line): A substance that takes up hydrogen ions, lowering a fluid's H+ concentration, either directly or by releasing hydroxide ions (OH−) that join H+ to form water. Also called alkaline. alkal- ashes of burned plants Taught in Acids, bases, pH and buffers.
basement membrane: The thin mat of proteins under every epithelium that anchors it to the tissue below. It has two parts: the basal lamina, made by the epithelial cells, and the reticular lamina, made by the tissue beneath. lamina thin sheet · reticul- little net Taught in Epithelial tissue.
bleeding around the brain (hee-muh-TOH-muh): Bleeding inside the skull around the brain. An epidural hematoma is usually arterial, between skull and dura, and lens-shaped; a subdural hematoma is usually from torn bridging veins, between dura and arachnoid, and crescent-shaped; a subarachnoid hemorrhage puts blood into the CSF. hemat- blood · -oma mass · hemorrhage bursting forth of blood Taught in Meninges, ventricles and cerebrospinal fluid.
blood as a connective tissue: Blood is a fluid connective tissue: red cells, white cells and platelets carried in a liquid matrix, plasma. Its fiber-forming protein stays dissolved until a clot forms. Taught in Connective tissue.
blood clot (basic): A jelly-like plug that seals a cut vessel: platelets clump at the damage, and a dissolved plasma protein forms sticky threads that trap red cells. Taught in Connective tissue.
blood flow and the flow equation (vessels): The volume of blood passing a point per minute. In any vessel, organ or the whole circuit it follows F = ΔP / R: the pressure difference between the two ends divided by the resistance. vascul- little vessel Taught in Blood pressure, flow and resistance.
blood potassium and the resting potential (hy-per-kuh-LEE-mee-uh): Because potassium leak sets most of the resting potential, blood potassium changes it. Hyperkalemia (high blood potassium) shrinks the potassium gradient and depolarizes cells; hypokalemia (low blood potassium) hyperpolarizes most cells. hyper- above · hypo- below · kal- potassium (Latin kalium) · -emia blood condition Taught in The resting membrane potential.
blood pressure (in detail) (sis-TOL-ik; dy-uh-STOL-ik): The pressure of blood in the large systemic arteries, which swings with each heartbeat between systolic pressure, the peak during ejection, and diastolic pressure, the lowest point just before the next ejection. It is written systolic over diastolic, for example 120/80 mm Hg. systol- contraction · diastol- dilation, expansion Taught in Blood pressure, flow and resistance.
blood pressure and blood volume (basic): Blood pressure is the pressure blood exerts on the walls of the blood vessels, usually measured in a large artery and written as the peak over the lowest value, such as 120/80 mm Hg. Blood volume is the total amount of blood, about 5 liters in an adult; less blood volume means less stretch of the vessel walls and a lower blood pressure. Taught in Gradients, pressure and flow.
blood supply of the lungs: The lungs' two blood supplies. The pulmonary arteries bring deoxygenated blood from the right ventricle to the alveolar capillaries for gas exchange. The bronchial arteries, systemic branches mostly of the thoracic aorta, bring oxygenated blood to the airway walls, connective tissue and visceral pleura; bronchial veins drain partly to the azygos system and partly into pulmonary veins. bronch- windpipe · pulmon- lung Taught in Trachea, bronchial tree, alveoli and lungs.
blood volume and blood pressure (in detail): The link between how much blood you have and your long-term blood pressure: more volume raises venous return, stroke volume and cardiac output, so MAP rises; less volume lowers them. Only restoring volume corrects a lasting change. Taught in Long-term blood pressure regulation.
blood–brain barrier: The brain capillary wall's control of what enters brain tissue: endothelial cells sealed by tight junctions, with no pores and few vesicles, maintained by astrocyte end-feet. Small lipid-soluble molecules cross freely, glucose and amino acids need carrier proteins, and most proteins, ions and water-soluble drugs are kept out. Taught in Meninges, ventricles and cerebrospinal fluid.
bone (osseous) tissue (OSS-ee-us): Osseous tissue: hard connective tissue whose matrix is collagen hardened by calcium-containing mineral crystals. It is rich in blood vessels, so it heals well. os-, oste- bone Taught in Connective tissue.
Boyle's law: For a fixed amount of gas at constant temperature, pressure and volume are inversely related: P₁ × V₁ = P₂ × V₂. Enlarging the alveoli lowers the pressure of the air inside them; shrinking them raises it. Taught in Pulmonary ventilation.
brain development (basic) (pros-en-SEF-uh-lon; mez-en-SEF-uh-lon; rom-ben-SEF-uh-lon): The neural plate folds into the neural tube (neurulation); its front end forms three primary brain vesicles (prosencephalon or forebrain, mesencephalon, rhombencephalon or hindbrain), then five secondary vesicles that become the cerebrum, diencephalon, midbrain, pons and cerebellum, and medulla. Neural crest cells form structures outside the CNS. neur- nerve · encephal- brain · pros- forward · mes- middle · rhomb- diamond shape · tel- end · met- after · myel- marrow Taught in Regions of the brain.
brainstem (ponz; meh-DUL-uh ob-long-GAH-tuh; kuh-LIK-yoo-lus): The stalk linking the cerebrum and diencephalon to the spinal cord: the midbrain (with the cerebral peduncles and the superior and inferior colliculi), the pons and the medulla oblongata. Its nuclei control heart rate, blood vessel diameter and breathing rhythm. pons bridge · medulla marrow · oblongata lengthened · colliculus little hill · pedunculus little foot Taught in Regions of the brain.
breathing during exercise and at altitude (hy-perp-NEE-uh): In exercise, ventilation rises to match carbon dioxide production with little change in blood gases (hyperpnea). At altitude, low PO2 drives ventilation through the carotid bodies, and acclimatization over days and weeks raises ventilation further and adds red blood cells; going up too fast can cause acute mountain sickness. hyper- over · -pnea breathing · ad- to Taught in Control of breathing.
bronchial tree (BRONG-kus; BRONG-kye; BRONG-kee-ohl): The branching airways of the lungs: primary (main) bronchi, secondary (lobar) and tertiary (segmental) bronchi, smaller bronchi, then bronchioles without cartilage, terminal bronchioles (the end of the conducting zone), respiratory bronchioles (the first with alveoli) and alveolar ducts. Down the tree, cartilage disappears, smooth muscle becomes relatively thicker and the epithelium thins. bronch- windpipe · -ole small Taught in Trachea, bronchial tree, alveoli and lungs.
buffer: A pair of substances, a weak acid and the weak base it becomes after releasing H+, that resists changes in pH by taking up or releasing hydrogen ions. It holds acid temporarily and can be used up. Taught in Acids, bases, pH and buffers.
bulk flow: The movement of a whole fluid, with everything dissolved or carried in it, from higher to lower pressure. Blood moving through vessels and air moving into the lungs are examples. Taught in Gradients, pressure and flow.
bundle, bundle branches and Purkinje fibers (HISS; pur-KIN-jee): The fast conducting path through the ventricles: the AV bundle (bundle of His) crosses the cardiac skeleton, splits into right and left bundle branches down the interventricular septum, and feeds the Purkinje fibers, a subendocardial conducting network. The moderator band carries part of the right branch to the right ventricle's front papillary muscle. sub- beneath · endo- within · cardi- heart Taught in The conduction system and pacemaker cells.
calcium-induced calcium release: Calcium-induced calcium release: calcium entering a cardiac muscle cell through L-type channels opens calcium release channels on the sarcoplasmic reticulum, which releases a much larger amount of calcium into the cytosol and starts contraction. induc- lead in, bring about Taught in Cardiac muscle cells and their action potential.
cancer as uncontrolled division (muh-TAS-tuh-sis): Disease in which cells that have gathered mutations divide without control and escape apoptosis. The resulting mass is a tumor (neoplasm); spread of its cells to distant sites is metastasis. neo- new · -plasm formed thing · meta- change · -stasis placement Taught in Cell division and differentiation.
capillary hydrostatic pressure (hy-droh-STAT-ik): The pressure of blood against the inside of a capillary wall (CHP), also called blood hydrostatic pressure. It pushes fluid out of the capillary, and falls from about 35 mm Hg at the arteriole end to about 15 mm Hg at the venule end. hydr/o water · -static standing, at rest Taught in Capillary exchange.
capillary types (FEN-es-tray-ted; sy-noo-SOYD; PAIR-ih-syte): Continuous capillaries have an unbroken endothelium; fenestrated capillaries have pores through their cells; sinusoids have large gaps and an incomplete basement membrane. An arteriole feeds a capillary bed; metarterioles, thoroughfare channels and arteriovenous anastomoses can shunt blood past it; pericytes wrap the wall; vasomotion is rhythmic arteriolar contraction. Precapillary sphincters are described classically, but their role in humans is unsettled. fenestra window · sinus hollow · peri- around · -cyte cell · meta- beyond · micro- small Taught in Structure of blood vessels.
carbohydrate (kar-bo-HY-drate; mon-o-SAK-uh-ride): A molecule of carbon, hydrogen and oxygen, roughly one carbon to two hydrogens to one oxygen. Monosaccharides are single sugar units, disaccharides are two joined, and polysaccharides are long chains; sugars are the small ones. carbo- carbon · hydrate water · sacchar/o sugar · di- two Taught in Carbohydrates, lipids, proteins and nucleic acids.
carbon dioxide and blood pH: Carbon dioxide forms carbonic acid, which releases hydrogen ions, so a higher PCO2 lowers blood pH and a lower PCO2 raises it. Normal arterial PCO2 is about 40 mmHg (35–45). Taught in Carbon dioxide transport.
carbon dioxide as a waste product of metabolism: The carbon dioxide cells make as they break down fuel, released when pyruvate loses a carbon and in the citric acid cycle. It diffuses into the blood and is breathed out; one glucose yields 6 CO2. Taught in How cells make ATP.
carbon dioxide as the main drive to breathe: Minute to minute, breathing is set mainly to hold arterial PCO2 near 40 mmHg: a small rise in PCO2 sharply increases ventilation, while low oxygen drives breathing strongly only once arterial PO2 falls below about 60 mmHg. Taught in Control of breathing.
carbon monoxide poisoning: Harm from carbon monoxide (CO), a colorless, odorless gas from incomplete burning. It binds heme about 200 to 250 times more tightly than oxygen (forming carboxyhemoglobin), lowers oxygen content, shifts the curve left and blocks mitochondria, while PO2 and a standard pulse oximeter reading stay normal. It is treated with 100% oxygen. mon- one · -oxide compound with oxygen Taught in Oxygen transport.
carbonic acid–bicarbonate buffer (by-KAR-bo-nate): The main buffer of blood: carbonic acid (H2CO3), a weak acid, paired with bicarbonate (HCO3−), a weak base. Bicarbonate takes up added H+ to form carbonic acid, which splits into water and carbon dioxide that is breathed out. bi- two · carbon- carbon · -ate salt of an acid Taught in Acids, bases, pH and buffers.
carbonic anhydrase (kar-BON-ik an-HY-drayz): The enzyme in red blood cells that speeds the reaction CO2 + H2O ⇌ H2CO3 by thousands of times, in whichever direction the concentrations push it: toward bicarbonate in the tissues and back to carbon dioxide in the lungs. an- without · hydr- water · -ase enzyme Taught in Carbon dioxide transport.
cardiac muscle tissue (KAR-dee-ak): Muscle tissue found only in the heart wall: short, branched, striated fibers with one central nucleus, joined by intercalated discs. It is involuntary. cardi- heart · -ac pertaining to Taught in Muscle tissue types.
cardiac output: The volume of blood one ventricle pumps per minute: heart rate times stroke volume (CO = HR × SV). It is about 5 L/min in a resting adult. cardi- heart · -ac pertaining to Taught in Cardiac output and its control.
cardiac reserve: The difference between a person's highest cardiac output and their cardiac output at rest: the extra pumping available on demand. Training raises it; age and heart disease lower it. Taught in Cardiac output and its control.
cardiac skeleton: Four rings of dense connective tissue around the heart valves, joined into one sheet between the atria and the ventricles. It holds the valve openings in shape, anchors the heart muscle, and blocks electrical signals from crossing straight from atria to ventricles. cardi/o heart · -ac pertaining to Taught in Heart valves, septa and internal structure.
cardiac tamponade (tam-poh-NAHD): Compression of the heart by blood or fluid collecting in the pericardial cavity. Because the fibrous pericardium cannot stretch quickly, pressure in the sac rises, the heart cannot fill between beats, and blood pressure falls. cardi/o heart · -ac pertaining to · tampon plug (French) Taught in Heart location, coverings, chambers and great vessels.
cardiovascular response to exercise: The changes exercise brings: higher heart rate, stroke volume and cardiac output, arteriole dilation in working muscle, less flow to the gut and kidneys, and a modest rise in MAP. Target heart rate is a chosen percentage of maximum heart rate, which is roughly 220 minus age. Taught in Short-term blood pressure regulation.
carrier saturation: The point at which every carrier protein in a membrane is occupied, so raising the concentration gradient no longer speeds transport. The rate at that point is the transport maximum. saturare to fill Taught in Passive transport across membranes.
cartilage (KON-droh-site; HYE-uh-lin): Firm, flexible, avascular connective tissue whose chondrocytes sit in pockets in a water-rich matrix, usually wrapped in a perichondrium. Its types are hyaline cartilage (smooth), fibrocartilage (thick collagen) and elastic cartilage (elastic fibers). chondr- cartilage · peri- around · hyal- glass Taught in Connective tissue.
cell: The smallest unit that can carry out the activities of life on its own. Cells are built from molecules and are the units that make up tissues. cella (Latin) small room Taught in Levels of organization and organ systems.
cell body, dendrites and axon (DEN-drite; AK-son): The cell body holds a neuron's nucleus and makes its proteins; dendrites are short branches that receive signals; the single axon carries the signal away, ending in axon terminals (synaptic end bulbs) that release chemicals onto the next cell. dendr- tree · axon axis Taught in Nervous tissue.
cell cycle: The ordered series of events from a cell's formation to its division: interphase (G1, S and G2, with DNA replicated in S) followed by the mitotic phase. A cell that stops cycling rests in G0. inter- between Taught in Cell division and differentiation.
cell differentiation: The process by which a cell becomes specialized in structure and function, by switching on one set of genes and keeping others off. The genome itself is not changed. differ- to carry apart Taught in Cell division and differentiation.
cell junction: A specialized spot where membrane proteins connect a cell to a neighboring cell or to the material around it. The three main types are tight junctions, desmosomes and gap junctions. junction a joining Taught in Cell junctions.
cellular respiration: The controlled breakdown of fuel molecules, such as glucose, inside cells, with the energy released captured as ATP. Broken down fully with oxygen, one glucose yields 6 CO2, 6 water and about 30–32 ATP. re- again · spir- breathe Taught in How cells make ATP.
central and peripheral nervous system (per-IF-er-ul): The central nervous system (CNS) is the brain and spinal cord, where integration happens. The peripheral nervous system (PNS) is everything else: the nerves, the ganglia along them and the sensory receptors at their ends. centr- center · peri- around · pher- carry Taught in Organization of the nervous system.
central chemoreceptors: Neurons near the front surface of the medulla oblongata that respond to hydrogen ions in the brain's fluid. Because carbon dioxide crosses the blood–brain barrier and hydrogen ions do not, they track arterial PCO2. chem- chemical · re- back · cept- take, receive Taught in Control of breathing.
cerebellum (sair-uh-BEL-um; uh-TAK-see-uh): The folded structure behind the brainstem that compares intended movement with actual movement and corrects force, timing and direction, and helps keep balance. Damage causes ataxia, clumsy uncoordinated movement on the same side. cerebellum little brain · a- without · tax- order Taught in Regions of the brain.
cerebral arterial circle (suh-REE-brul; BAS-ih-lur): A ring of connected arteries under the brain, also called the circle of Willis: the anterior communicating artery, the anterior cerebral arteries, the internal carotids, the posterior communicating arteries and the posterior cerebral arteries from the basilar artery. It is an anastomosis that can reroute blood around a slowly narrowed artery. cerebr- brain · basi- base Taught in The major systemic arteries.
cerebral lateralization: Differences in function between the two cerebral hemispheres: language is handled mainly by the left hemisphere in most people, and spatial attention, face recognition and the emotional tone of speech mainly by the right. The corpus callosum shares information between them. later- side Taught in Cortical functions, memory, language and sleep.
cerebrospinal fluid (suh-REE-broh-SPY-nul; KOR-oyd PLEK-sus; hy-droh-SEF-uh-lus): Cerebrospinal fluid: the clear fluid secreted mainly by the choroid plexuses (about 500 mL a day) that fills the ventricles and subarachnoid space, floats and cushions the brain, and returns to venous blood, classically through the arachnoid granulations. Excess CSF enlarging the ventricles is hydrocephalus; a lumbar puncture samples it. cerebr- brain · spin- spine · choroid membrane-like · plexus braid · hydro- water · cephal- head Taught in Meninges, ventricles and cerebrospinal fluid.
cerebrum (suh-REE-brum; JY-rus; SUL-kus): The largest part of the brain: two cerebral hemispheres separated by the longitudinal fissure and joined by the corpus callosum. Its outer layer, the cerebral cortex, is gray matter folded into gyri and sulci over a core of white matter that includes the internal capsule. cerebrum brain · hemi- half · cortex bark · gyrus circle · sulcus furrow · corpus callosum tough body Taught in Regions of the brain.
chambers of the heart (AY-tree-um; VEN-trih-kul; truh-BEK-yoo-lee KAR-nee-ee): The four spaces inside the heart: two upper atria that receive blood from veins and two lower ventricles that pump blood into arteries. Surface grooves (the coronary and interventricular sulci) mark their boundaries; auricles, pectinate muscles and trabeculae carneae are features of their walls. atri- entrance hall · ventricul- little belly · auricul- little ear · pectin- comb · trabecula little beam · carne- flesh · sulcus groove Taught in Heart location, coverings, chambers and great vessels.
characteristics and requirements of life: The features all living things share: organization, metabolism (the sum of all chemical changes in the body), responsiveness, movement, growth, development and reproduction. Staying alive also depends on oxygen, nutrients, water, a narrow temperature range and suitable air pressure. meta- change · bol throw Taught in Levels of organization and organ systems.
charge separation: A state in which positive and negative charges are held apart by a barrier, so one region has extra positive charge and a nearby region extra negative charge. Separating charge takes energy, which is stored as potential energy; in your cells, a very thin layer of separated charge lines the two faces of the membrane. Taught in Charge, voltage and current.
chemical level of organization: The smallest level of organization: atoms, the smallest units of an element, and molecules, the units formed when atoms bond together. Taught in Levels of organization and organ systems.
chemical messenger: A molecule that one cell releases to change the activity of another cell (also called a signaling molecule). It acts only on cells with receptor proteins that bind it. Taught in Chemical messengers and receptors.
chemical reaction: A process that breaks and forms chemical bonds, turning reactants into products without creating or destroying atoms. A synthesis reaction joins reactants into a larger product; a decomposition reaction splits a reactant into smaller products. syn- together · de- apart Taught in Atoms, ions and chemical bonds.
chemical synaptic transmission: Signaling across a synaptic cleft by a neurotransmitter: an action potential opens voltage-gated calcium channels in the axon terminal, calcium triggers exocytosis of synaptic vesicles, the neurotransmitter diffuses across and binds receptor proteins on the postsynaptic membrane, and it is then removed. Taught in Synapses and neurotransmitters.
chloride shift: The one-for-one exchange of bicarbonate for chloride across the red blood cell membrane through the carrier protein band 3. In the tissues bicarbonate leaves and chloride enters; in the lungs the exchange reverses. It is passive and uses no ATP. Taught in Carbon dioxide transport.
chromatin and chromosomes (KROH-muh-tin; KROH-muh-sohm): Chromatin is DNA wound around histone proteins into nucleosomes and folded further. A chromosome is one DNA molecule with its proteins; once copied, it has two identical sister chromatids joined at the centromere. chromo- color · -some body · centro- center · -mere part · auto- self Taught in The nucleus, DNA and genes.
chronic obstructive pulmonary disease (em-fih-SEE-muh): Chronic obstructive pulmonary disease: long-lasting lung disease with airflow obstruction that does not fully reverse (FEV1 ÷ FVC below 0.70 after a drug that opens the airways), mainly from smoking. Its two main forms are emphysema, the destruction of alveolar walls, and chronic bronchitis, a daily cough with excess mucus for at least three months in two years in a row. em- in · physa- to blow · bronch- windpipe branch · -itis inflammation Taught in Respiratory disorders.
cilia and flagella (SIL-ee-uh; fluh-JEL-uh): Mobile projections of the cell surface with a core of microtubules. Cilia are short and numerous and move fluid across the cell surface; a flagellum is long and single and moves the cell, as in a sperm. cilium eyelash · flagellum little whip Taught in Organelles and the cytoskeleton.
circulatory shock: Failure of the circulation to deliver enough oxygen to the tissues, so cells switch to anaerobic metabolism and lactate rises. Hypovolemic shock comes from too little volume, cardiogenic shock from a failing pump, and obstructive shock from a blockage of flow into or out of the heart. hypo- below · vol- volume · -emia blood condition · cardi/o heart · -genic produced by Taught in Hypertension, heart failure and shock.
classifying epithelia (SKWAY-mus): Epithelia are named by layers and by the shape of the surface cells. Simple means one layer and stratified means two or more; squamous cells are flat, cuboidal cells are cube-shaped and columnar cells are tall. strat- layer · squam- scale Taught in Epithelial tissue.
classifying neurons (SOO-doh-yoo-nih-POH-ler): By shape, neurons are multipolar (one axon, many dendrites), bipolar (one axon, one dendrite) or unipolar, also called pseudounipolar (one process that splits in two). By job, they are sensory neurons (toward the CNS), interneurons (within the CNS) or motor neurons (out to effectors). multi- many · bi- two · uni- one · pseudo- false · pol- pole · inter- between Taught in Neurons and glial cells.
colloid osmotic pressure (KOL-oyd oz-MOT-ik; on-KOT-ik): The osmotic pressure made by dissolved proteins that cannot cross the wall between two fluids; also called oncotic pressure. In plasma (blood colloid osmotic pressure, BCOP) it is about 25 mm Hg, mostly from albumin, and it pulls fluid into capillaries. koll- glue · -oid like · onc/o mass, bulk Taught in Capillary exchange.
compensation for hemorrhage: The body's responses to blood loss: the baroreceptor reflex within seconds, movement of interstitial fluid into the plasma over hours, the RAAS, ADH and thirst over a day, and replacement of plasma proteins and red blood cells over days to weeks. hem/o blood · -rrhage bursting forth Taught in Hypertension, heart failure and shock.
concentration (of a solution): The amount of solute in a given volume of solution: amount divided by volume. For electrolytes it is usually given in millimoles per liter (mmol/L), a unit that counts particles. con- together · centr/o center Taught in Water, solutions and concentration.
conducting and respiratory zones: The two functional divisions of the respiratory tract. The conducting zone (nasal cavity, pharynx, larynx, trachea and the air tubes down to the last ones without alveoli) filters, warms, humidifies and delivers air; the respiratory zone (the smallest airways that carry alveoli, and the alveoli) is where oxygen and carbon dioxide cross between air and blood. con- together · duc- to lead · re- again · spir- to breathe Taught in Nose, pharynx and larynx.
conduction velocity: The speed at which an action potential travels along an axon, from about 0.5 m/s in thin unmyelinated fibers to about 120 m/s in wide myelinated ones. It rises with axon diameter, myelination and temperature. velocitas speed (Latin) Taught in The action potential in detail.
connective tissue: Tissue made of relatively few cells scattered in a large extracellular matrix of ground substance and fibers. Its groups are connective tissue proper (loose and dense), supportive connective tissue (cartilage and bone) and fluid connective tissue (blood). extra- outside Taught in Connective tissue.
connective tissue fibers (KOL-uh-jen; ee-LAS-tin): Protein fibers in the matrix: collagen fibers are strong when pulled but barely stretch, elastic fibers (made of elastin) stretch and recoil, and reticular fibers are thin collagen strands that form supporting nets. kolla glue · -gen producing · reticul- little net Taught in Connective tissue.
consciousness and sleep (ee-LEK-troh-en-SEF-uh-loh-gram): Consciousness needs the reticular activating system and the cerebral cortex. The EEG records the cortex's summed synaptic potentials: fast small waves when awake, slow large waves in deep sleep. Sleep cycles about every 90 minutes through non-REM stages N1, N2 and N3 and REM sleep, when the EEG looks awake, the eyes dart, dreams are vivid and most skeletal muscles are paralyzed. electro- electric · encephal- brain · -gram record Taught in Cortical functions, memory, language and sleep.
continuous conduction: The way an action potential travels along an unmyelinated axon: every patch of membrane fires in turn, each next to the last. It is slow, about 0.5 to 2 m/s. continuus joined, uninterrupted (Latin) Taught in The action potential in detail.
contractile cardiac muscle cell (KAR-dee-oh-MY-oh-site): A working muscle cell of the heart wall (a cardiomyocyte): short, branched and striated, with one or two central nuclei, many mitochondria, and intercalated discs whose gap junctions pass action potentials to its neighbors. It rests at about −90 mV and fires only when charge from a neighbor brings it to threshold. cardi/o heart · my/o muscle · -cyte cell Taught in Cardiac muscle cells and their action potential.
contractility (in-oh-TROH-pee): The strength of contraction at any given stretch, set by how much calcium reaches the cross-bridges. Positive inotropic factors such as norepinephrine and epinephrine raise it; negative inotropic factors such as beta blockers, calcium channel blockers, acidosis and hyperkalemia lower it. ino- fiber · trop- turning, influencing Taught in Cardiac output and its control.
control center: The part of a feedback loop that receives input from the afferent pathway, compares it with the set point, and sends commands along the efferent pathway (also called the integrating center). Taught in Homeostasis and feedback loops.
control of heart rate (kron-oh-TROH-pik): Heart rate is set by the cardiovascular center in the medulla oblongata. Its cardioaccelerator center speeds the SA node through sympathetic nerves and the cardiac plexus; its cardioinhibitory center slows it through the vagus nerves. Factors that change heart rate are called chronotropic. chron- time · trop- turning, influencing · plexus braid, network Taught in Cardiac output and its control.
control of the cell cycle (SY-klin): The system that decides when a cell moves through the cell cycle. Cyclins bind and switch on cyclin-dependent kinases (CDKs), which push the cell forward, and checkpoints pause it until conditions are met. Oncogenes are overactive division-promoting genes; tumor suppressor genes normally restrain division. kin- to move · -ase enzyme · onco- tumor Taught in Cell division and differentiation.
coronary circulation (KOR-uh-nair-ee): The heart muscle's own blood supply. The right and left coronary arteries leave the aorta just above the aortic valve and branch (left anterior descending, circumflex, marginal and posterior interventricular arteries); cardiac veins drain into the coronary sinus, which empties into the right atrium. coron- crown · circum- around · flex- bend Taught in Blood flow through the heart and the two circuits.
covalent bond (ko-VAY-lent): A bond in which two atoms share one or more pairs of electrons (single, double or triple bonds). The strongest bonds in the molecules of your body. co- together · valent strength Taught in Atoms, ions and chemical bonds.
cutaneous membrane (kyoo-TAY-nee-us): The skin: a keratinized stratified squamous epidermis on a dermis of dense irregular connective tissue. It is the only dry membrane. cutane/o skin Taught in Body membranes and tissue repair.
cytokinesis (sy-toh-kih-NEE-sis): Division of the cytoplasm at the end of the mitotic phase. A ring of actin and myosin tightens around the middle of the cell, deepening a cleavage furrow until the cell pinches in two. cyto- cell · kinesis movement Taught in Cell division and differentiation.
cytoskeleton (sy-toh-SKEL-eh-ton): The network of protein fibers in the cytoplasm: microfilaments (actin), intermediate filaments and microtubules. It shapes the cell, holds organelles, provides tracks for transport and, with motor proteins such as myosin, produces movement. Microtubules grow from the centrosome, which holds a pair of centrioles. cyto- cell · centr- center Taught in Organelles and the cytoskeleton.
dead space: Air that is breathed in and out but takes no part in gas exchange. Anatomical dead space is the volume of the conducting airways, about 150 mL; alveolar dead space is alveoli that get air but no blood flow; total dead space is the two added together. anatom- cutting up (structure) · alveol- small cavity Taught in Lung volumes and ventilation rates.
demyelinating disease (dee-my-uh-lin-AY-shun): Damage to or loss of the myelin sheath, which lets current leak out between nodes so conduction slows or fails. Multiple sclerosis, in which the immune system attacks CNS myelin, is the commonest demyelinating disease. de- remove · myel- marrow (root of myelin) · scler- hard · -osis condition Taught in The action potential in detail.
dense connective tissue: Connective tissue packed with thick collagen bundles and few cells. In dense regular tissue the bundles run parallel (tendons, ligaments); in dense irregular tissue they run every way (dermis, organ capsules). Taught in Connective tissue.
depolarization, repolarization and hyperpolarization: Depolarization: the membrane potential becomes less negative than rest. Repolarization: it returns toward rest after a depolarization. Hyperpolarization: it becomes more negative than rest. de- away from, removing · re- again · hyper- above, beyond Taught in The resting membrane potential.
dermatomes (DER-muh-tome): A dermatome is the strip of skin whose sensory axons travel in one spinal nerve and enter the cord through one dorsal root. Neighboring dermatomes overlap, so damage to one root reduces sensation rather than abolishing it. derm- skin · -tome cut, section Taught in Spinal nerves and plexuses.
desmosome (DEZ-moh-sohm): A button-shaped anchoring junction in which cadherins grip across the gap between two cells and dense plaques anchor intermediate filaments on each side. It holds cells together against pulling. desmos bond · -some body Taught in Cell junctions.
diaphragm (DY-uh-fram): A dome-shaped sheet of muscle that separates the thoracic cavity from the abdominopelvic cavity. When it contracts, the dome flattens and moves down, which enlarges the thoracic cavity; it is the main muscle of breathing. diaphragma (Greek) partition Taught in Body cavities and serous membranes.
diencephalon (dy-en-SEF-uh-lon; THAL-uh-mus): The central part of the brain between the cerebrum and the brainstem, made of the thalamus, hypothalamus and epithalamus. The thalamus relays and filters almost all input to the cerebral cortex. di- through · encephal- brain · thalamus inner chamber · epi- upon Taught in Regions of the brain.
diffusion (dih-FYOO-zhun): The spreading of particles from where they are more concentrated to where they are less concentrated, driven by their own random motion. Net diffusion is the overall movement left after subtracting the particles crossing one way from those crossing the other; it stops at equilibrium, though the particles keep moving. dif- apart · fus- pour Taught in Diffusion and osmosis.
diffusion across capillaries: The net movement of each solute between plasma and interstitial fluid, down its own concentration gradient. Lipid-soluble substances such as oxygen and carbon dioxide pass through the endothelial cells; small water-soluble ones pass through the clefts between them. capill- hair (capillaris = hair-like) · diffus- spread out Taught in Capillary exchange.
distributive shock: Shock caused by widespread vasodilation, which drops TPR and pools blood in dilated vessels; also called vascular shock. Its main forms are septic shock (from sepsis, the body's poorly controlled response to an infection), neurogenic shock (loss of sympathetic tone) and shock from a severe allergic reaction. sept- rotting · neur/o nerve Taught in Hypertension, heart failure and shock.
DNA (dee-OK-see-ry-boh-noo-KLAY-ik): Deoxyribonucleic acid: two antiparallel strands of nucleotides twisted into a double helix, held together by base pairing (A with T, G with C). Its base sequence stores inherited information. de- removed · oxy- oxygen · helix spiral Taught in The nucleus, DNA and genes.
DNA replication (puh-LIM-er-ayz): The copying of DNA before a cell divides. Helicase separates the strands, and DNA polymerase builds a new complementary strand on each old one, giving two identical molecules that each keep one old strand. helic- spiral · poly- many · -ase enzyme Taught in The nucleus, DNA and genes.
dorsal and ventral rami (RAY-mus, RAY-my): The branches a spinal nerve splits into just outside the intervertebral foramen. The dorsal ramus supplies the deep back muscles and the skin of the back; the larger ventral ramus supplies the front and sides of the trunk and the limbs. Both are mixed. ramus branch Taught in Spinal nerves and plexuses.
dorsal and ventral roots (GANG-glee-on): The two roots connecting each side of a spinal cord segment to the body. The dorsal (posterior) root carries sensory axons in and has a dorsal root ganglion holding their cell bodies; the ventral (anterior) root carries motor axons out. Beyond the ganglion they join into one nerve. ganglion swelling, knot Taught in The spinal cord.
dorsal body cavity: The posterior main body cavity: the cranial cavity inside the skull, which holds the brain, and the vertebral canal inside the backbone, which holds the spinal cord. Both parts are walled in by bone. dorsum (Latin) back · crani/o skull Taught in Body cavities and serous membranes.
ECG intervals and segments: Timed stretches of the ECG. The PR interval (start of P to start of QRS, 0.12 to 0.20 second) is mostly AV nodal delay; the ST segment (end of QRS to start of T) is the flat plateau when the ventricles are fully depolarized; the QT interval (start of QRS to end of T) spans the ventricular action potential. inter- between Taught in The electrocardiogram.
ECG waves: The three deflections of a normal beat: the P wave (atrial depolarization), the QRS complex (ventricular depolarization, which hides atrial repolarization) and the T wave (ventricular repolarization). Taught in The electrocardiogram.
edema (eh-DEE-muh): An excess of fluid in the interstitial spaces, which forms when fluid filters out of capillaries faster than it drains away. Causes are higher capillary pressure, lower plasma protein, leaky capillary walls, or blocked drainage; widespread swelling is systemic edema. oidema swelling (Greek) Taught in Capillary exchange.
effector: The cell, tissue or organ that carries out the control center's command and so changes the regulated variable; almost always a muscle or a gland. effect- to bring about · -or one who does Taught in Homeostasis and feedback loops.
efferent pathway (EF-er-ent): The route that carries commands away from the control center to the effector: nerves carrying action potentials, or a hormone traveling in the blood. ef- (ex-) away from · fer to carry Taught in Homeostasis and feedback loops.
eicosanoids (eye-KOH-suh-noyds): Local lipid messengers made on demand from a 20-carbon fatty acid cut out of membrane phospholipids. They include prostaglandins, which sensitize pain-sensing nerve endings and dilate small vessels, and leukotrienes, which constrict airways. eicosa- twenty (Greek) · leuko- white Taught in Chemical messengers and receptors.
ejection fraction: The share of the end-diastolic volume that a ventricle ejects in one beat: EF = SV ÷ EDV × 100. A normal left ventricular value is about 50 to 70 percent. e- out · ject- throw Taught in The cardiac cycle.
elastic and muscular arteries: Elastic arteries, the largest arteries near the heart, have many elastic fibers in the tunica media; they stretch during ejection and recoil in diastole. Muscular arteries, farther out, have a thick smooth muscle media and distribute blood to organs. Taught in Structure of blood vessels.
electric charge: A property of particles that makes them push or pull on each other. Protons carry positive charge and electrons negative charge; opposite charges attract and like charges repel. electr/o electricity Taught in Atoms, ions and chemical bonds.
electrical current: The flow of electric charge, measured in amperes. In your body it is an ion current, carried by ions moving through fluid or across a membrane; by convention its direction is the direction positive charge moves, and current equals voltage divided by electrical resistance. curr- run Taught in Charge, voltage and current.
electrical synapse: A synapse where gap junctions join two neurons, so ions and current pass directly from one to the other. It is almost instant, usually two-way, and makes coupled neurons fire in step. Taught in Synapses and neurotransmitters.
electrocardiogram (ee-lek-troh-KAR-dee-oh-gram): The electrocardiogram (ECG, also EKG): a graph over time of the summed voltage changes of the heart, recorded from electrodes on the skin. Each lead is one view, the voltage between a positive electrode and a reference; a standard 12-lead ECG uses 10 electrodes. electro- electric · cardio- heart · -gram record Taught in The electrocardiogram.
electrochemical gradient (ee-LEK-troh-KEM-ih-kul): The total push on an ion: its concentration gradient combined with the electrical gradient (the voltage), which pushes positive ions toward the negative side and negative ions toward the positive side. The two parts can add together or oppose each other. electr/o electric · chem- chemical Taught in Charge, voltage and current.
electrolyte (ee-LEK-tro-lite): A substance that separates into ions when it dissolves in water, so the water conducts electricity. In clinical use, the dissolved ions themselves, such as sodium, potassium, chloride and calcium. electr/o electricity · -lyte able to be loosened Taught in Atoms, ions and chemical bonds.
elements and compounds: Matter is anything that has mass and takes up space. An element is a substance made of one kind of atom, listed in the periodic table by atomic number; a compound is two or more different elements joined in a fixed ratio. com- together · pon/o to put Taught in Atoms, ions and chemical bonds.
end-diastolic and end-systolic volume (dy-AS-toh-lee; SIS-toh-lee): End-diastolic volume (EDV) is the volume in a ventricle at the end of diastole, just before it contracts (about 120 mL at rest). End-systolic volume (ESV) is the volume left at the end of systole, after ejection (about 50 mL at rest). dia- apart · systole contraction Taught in The cardiac cycle.
ending the synaptic signal: The clearing of a neurotransmitter from the synaptic cleft, which ends its signal: by diffusion away, by degradation (enzymes such as acetylcholinesterase break it down), or by reuptake (transporter proteins carry it back into the axon terminal or nearby astrocytes). re- back Taught in Synapses and neurotransmitters.
endocrine gland (EN-doh-krin): A ductless gland that releases hormones into the interstitial fluid, from where they diffuse into capillaries and travel in the blood to target cells. endo- within · -crine to secrete Taught in Glands: endocrine and exocrine.
endocytosis (en-doh-sy-TOH-sis; fag-oh-sy-TOH-sis; pin-oh-sy-TOH-sis): Taking material into a cell by folding a patch of plasma membrane around it and pinching it off as a vesicle. Its forms are phagocytosis (large particles), pinocytosis (droplets of fluid) and receptor-mediated endocytosis (specific substances bound to matching membrane proteins). endo- within · cyto- cell · -osis process · phago- eating · pino- drinking Taught in Active transport and vesicles.
endoplasmic reticulum (en-doh-PLAZ-mik reh-TIK-yoo-lum): A network of membrane sacs and tubes in the cytoplasm. Rough ER is studded with ribosomes and folds new proteins; smooth ER has no ribosomes and makes lipids, breaks down some drugs and stores calcium ions. endo- within · -plasm formed material · reticulum little net Taught in Organelles and the cytoskeleton.
energy (forms of) (ex-er-GON-ik, en-der-GON-ik): Energy is the capacity to do work. Potential energy is stored energy (chemical energy is potential energy held in the arrangement of atoms and bonds); kinetic energy is the energy of motion, including heat. An exergonic reaction releases energy, and an endergonic reaction takes energy in. kinet- motion · ex- out · end- within · erg- work Taught in Energy, metabolism and enzymes.
enzyme (EN-zime): A biological catalyst, almost always a protein. Its substrate binds a pocket called the active site, and the enzyme lowers the activation energy, the energy the reactants must gain before they can react. en- in · zyme leaven (yeast) · sub- under Taught in Energy, metabolism and enzymes.
epithelium (ep-ih-THEE-lee-um): A sheet of tightly joined cells that covers a body surface or lines a lumen. Its apical surface faces the open space, its basal surface rests on a basement membrane, and it has no blood vessels of its own. epi- upon · thel- originally nipple; a thin covering layer · a- without · vascul- small vessel Taught in Epithelial tissue.
equilibrium potential (ee-kwih-LIB-ree-um): The membrane voltage at which one ion has no net movement, because its electrical gradient exactly cancels its concentration gradient. About −90 mV for potassium and +60 mV for sodium. equi- equal · libra balance (Latin) Taught in The resting membrane potential.
excitable cell: A cell whose membrane can produce an action potential, because it has voltage-gated sodium and potassium channels. Neurons and muscle fibers are the main excitable cells. excitare to rouse (Latin) Taught in Electrical signals: graded potentials and action potentials.
excitatory and inhibitory postsynaptic potentials: Graded potentials caused by a neurotransmitter in a postsynaptic neuron. An excitatory postsynaptic potential (EPSP) is a small depolarization toward threshold; an inhibitory postsynaptic potential (IPSP) hyperpolarizes the membrane or holds it near rest, away from threshold. ex- out · citare to set in motion (Latin) · inhibere to hold back (Latin) Taught in Synapses and neurotransmitters.
exocrine gland (EK-soh-krin): A gland whose product travels through a duct, or for a single-cell gland directly, onto a surface such as the skin or the inside of the gut. A serous gland releases watery, enzyme-rich fluid; a mucous gland releases mucus. exo- outside · -crine to secrete · ser/o watery fluid Taught in Glands: endocrine and exocrine.
exocytosis (ek-soh-sy-TOH-sis): Release of material from a cell when a vesicle fuses with the plasma membrane and empties its contents outside. It is how cells secrete products, and it adds the vesicle's membrane and proteins to the cell surface. exo- outside · cyto- cell · -osis process Taught in Active transport and vesicles.
expiration: Breathing out (exhalation). Quiet expiration is passive elastic recoil of the lungs and chest wall, which raises alveolar pressure above atmospheric. Forced expiration adds the internal intercostals and abdominal wall muscles. One inspiration plus one expiration is a respiratory cycle. ex- out · spir- to breathe Taught in Pulmonary ventilation.
external respiration: Gas exchange between alveolar air and blood in the pulmonary capillaries: oxygen diffuses into the blood and carbon dioxide diffuses out, each down its partial pressure gradient. extern- outside · pulmon- lung Taught in Gas exchange.
facilitated diffusion (fuh-SIL-ih-tay-ted): Passive movement of a substance down its gradient through a specific membrane protein: a channel, or a carrier protein that binds the substance, changes shape and releases it on the other side. Glucose enters most cells this way. facilis easy Taught in Passive transport across membranes.
factors that change enzyme activity: Temperature, pH, the amounts of substrate and enzyme, helpers and inhibitors all change how fast an enzyme works. A cofactor is a non-protein helper, often a metal ion; a coenzyme is an organic cofactor, often made from a vitamin. co- together Taught in Energy, metabolism and enzymes.
factors that set diffusion rate: Net diffusion is faster with a steeper concentration gradient, a higher temperature, smaller particles, a larger surface area to cross, a shorter diffusion distance and a barrier that the particle crosses easily. The time to diffuse grows with the square of the distance, so diffusion works only over very short distances. Taught in Diffusion and osmosis.
fetal hemoglobin (FEE-tal): The hemoglobin of a fetus (HbF), with two alpha and two gamma chains. It binds 2,3-BPG weakly, so it holds oxygen more tightly than adult hemoglobin (P50 about 19 mm Hg) and can take oxygen from maternal blood. It is mostly replaced by adult hemoglobin by about six months after birth. fet- offspring Taught in Oxygen transport.
fibroblast (FYE-broh-blast): The main cell of connective tissue proper, which makes fibers and ground substance. A less active one that maintains the matrix is called a fibrocyte. fibro- fiber · -blast builder, germ · -cyte cell Taught in Connective tissue.
filtration: Movement of water and small solutes through a membrane or thin barrier, pushed by a hydrostatic pressure gradient. Particles too large for the openings, such as blood cells, stay behind. filtrum felt, used to strain liquids Taught in Passive transport across membranes.
flow equals pressure gradient divided by resistance: Flow equals the pressure gradient divided by resistance: F = ΔP/R. Doubling the pressure gradient doubles flow; doubling the resistance halves it. Taught in Gradients, pressure and flow.
flow velocity and cross-sectional area: Blood velocity equals flow divided by the total cross-sectional area of the vessels at that level. The capillaries together have the largest total area, so blood moves slowest there, about 0.3 mm/s, compared with about 30 cm/s in the aorta. veloc- swift Taught in Blood pressure, flow and resistance.
fossa ovalis (FOSS-uh oh-VAL-iss): A shallow oval dip in the interatrial septum, seen from the right atrium. It marks where an opening between the atria sealed after birth. fossa shallow pit · ovalis oval Taught in Heart valves, septa and internal structure.
Frank–Starling mechanism: The heart's built-in property that a more-filled, more-stretched ventricle contracts more forcefully and ejects more, so stroke volume rises with end-diastolic volume. It keeps the outputs of the two ventricles matched. Taught in Cardiac output and its control.
frontal plane (koh-ROH-nul): A vertical plane that divides the body into anterior (front) and posterior (back) parts. It is also called the coronal plane. corona (Latin) crown Taught in Body planes and sections.
functional areas of the cortex (BROHD-mahnz): Areas of the cerebral cortex with particular jobs (localization of function), many known by Brodmann's area numbers. Primary areas send out movement (primary motor cortex, precentral gyrus) or first receive a sense (primary somatosensory cortex in the postcentral gyrus, primary visual and auditory cortex); association areas plan movement or interpret one sense; multimodal integration areas combine senses; the prefrontal cortex runs executive function. pre- before · post- after · soma body · multi- many Taught in Cortical functions, memory, language and sleep.
ganglion, nucleus and tract (GANG-glee-on): A cluster of neuron cell bodies is a nucleus in the CNS and a ganglion in the PNS. A bundle of axons is a tract in the CNS and a nerve in the PNS. ganglion swelling, knot · nucle- kernel · tract- drawn out Taught in Organization of the nervous system.
gap junction: A cluster of protein tunnels, each made of two docked connexons of six connexins, that connects the cytoplasm of neighboring cells. Water, ions and small molecules pass through, so electrical current can spread from cell to cell. Taught in Cell junctions.
gene (JEEN; JEE-nohm): A segment of DNA whose base sequence codes for a working product, usually a protein. The genome is all the DNA in one set of chromosomes: about 3.1 billion base pairs and roughly 20,000 protein-coding genes in humans. gen- to produce · -ome the whole set Taught in The nucleus, DNA and genes.
gene expression and its regulation (PROH-tee-ohm): Using a gene to make its product. Cells control which genes they express, mainly through transcription factors, proteins that bind DNA near a gene and raise or lower its transcription. The proteome is the full set of proteins a cell holds at a given time. prote- protein · -ome the whole set Taught in From gene to protein.
genetic code (KOH-don): The table that matches each three-base codon in mRNA to one amino acid or to a stop signal: 64 codons, 61 naming amino acids and 3 stops. A tRNA's anticodon pairs with its codon. anti- opposite Taught in From gene to protein.
gland: One cell or a group of epithelial cells that makes a product and releases it (secretion). glans acorn Taught in Glands: endocrine and exocrine.
glia of the CNS (AS-troh-site; oh-lih-goh-DEN-droh-site; my-KROH-glee-uh; eh-PEN-dih-mul): The four glial cells of the CNS: astrocytes (regulate the fluid around neurons, wrap capillaries, form scars), oligodendrocytes (myelinate segments of many axons), microglia (resident immune cells that engulf debris) and ependymal cells (line the fluid-filled spaces of the brain and spinal cord). astr- star · oligo- few · dendr- branch · micro- small · ependyma upper garment · -cyte cell Taught in Neurons and glial cells.
glia of the PNS (SHWAHN): The two glial cells of the PNS: Schwann cells, which myelinate one segment of one axon or cradle several unmyelinated axons and guide axon regrowth, and satellite cells, which cover neuron cell bodies in ganglia. satelles attendant Taught in Neurons and glial cells.
glial cell (GLEE-ul): A support cell of nervous tissue (also called glia or neuroglia). Glial cells hold neurons in place, wrap and insulate axons, control the fluid around neurons and engulf debris, and unlike mature neurons they can divide. glia glue Taught in Nervous tissue.
glucose (GLOO-kose): A six-carbon monosaccharide (C6H12O6) that dissolves in the liquid part of your blood and is the main fuel your cells, especially brain cells, break down for energy. gluc/o, glyc/o sweet, sugar · -ose sugar Taught in Carbohydrates, lipids, proteins and nucleic acids.
glycocalyx (gly-koh-KAY-liks): The coat of sugar chains attached to proteins (glycoproteins) and lipids on the outer surface of the plasma membrane. It marks cell identity, cushions the cell and helps cells recognize each other. glyco- sugar · calyx husk or cup Taught in The cell and its plasma membrane.
glycogen (GLY-ko-jen): A heavily branched polysaccharide of glucose that your liver and muscles build after meals. Liver glycogen is split to release glucose into the blood between meals; muscle glycogen fuels only the muscle that stores it. glyc/o sugar · -gen producing Taught in Carbohydrates, lipids, proteins and nucleic acids.
glycolysis (gly-KOL-ih-sis; py-ROO-vayt): The first stage of glucose breakdown: ten enzyme reactions in the cytosol that split one glucose into two pyruvate, with a net gain of 2 ATP and 2 NADH. It does not use oxygen. glyco- sugar · -lysis splitting · pyr- fire · uv- grape Taught in How cells make ATP.
Golgi apparatus (GOHL-jee): A stack of flattened membrane sacs that modifies, sorts and packages proteins arriving from the ER and sends them in vesicles to the plasma membrane, out of the cell, or to lysosomes. With the ER, vesicles, lysosomes and plasma membrane it forms the endomembrane system. endo- within Taught in Organelles and the cytoskeleton.
graded potential: A small, short-lived change in membrane potential whose size depends on the strength of the stimulus. It can depolarize or hyperpolarize, fades within a millimeter or two, and can add to other graded potentials. Taught in Electrical signals: graded potentials and action potentials.
gradient (GRAY-dee-ent): A difference in some quantity between two places, such as a concentration gradient (a difference in concentration) or a temperature gradient. Things move down a gradient, from more to less, without an energy input; its steepness is the difference divided by the distance. grad- step Taught in Gradients, pressure and flow.
gray matter and white matter: Gray matter is CNS tissue rich in neuron cell bodies, dendrites and axon terminals, where integration happens. White matter is CNS tissue made mostly of axon bundles wrapped in fatty glial layers, which carry signals between regions. Taught in Organization of the nervous system.
great vessels (VEE-nuh KAY-vuh; ay-OR-tuh): The large vessels at the base of the heart: the superior and inferior venae cavae (into the right atrium), the pulmonary trunk (out of the right ventricle, splitting into the right and left pulmonary arteries), the pulmonary veins (into the left atrium) and the aorta (out of the left ventricle, rising as the ascending aorta and curving over as the aortic arch). vena vein · cava hollow · pulmon- lung Taught in Heart location, coverings, chambers and great vessels.
Haldane effect (HAWL-dayn): The less oxygen hemoglobin carries, the more carbon dioxide the blood can carry, because deoxyhemoglobin binds more hydrogen ions and more carbon dioxide. It helps blood load carbon dioxide in the tissues and unload it in the lungs. Taught in Carbon dioxide transport.
heart failure: A condition in which the heart cannot pump enough blood for the body's needs, or can only do so at abnormally high filling pressures. Left-sided failure backs blood up into the lungs; right-sided failure backs it up into the systemic veins; congestive heart failure names the resulting congestion. Taught in Hypertension, heart failure and shock.
heart sounds (sten-OH-sis; ree-gur-jih-TAY-shun): The sounds of each beat, heard as lub-dub: S1 (lub) from closure of the atrioventricular valves at the start of ventricular systole, and S2 (dub) from closure of the semilunar valves at its end. A murmur is the sound of turbulent flow, usually through a narrowed (stenotic) or leaking (regurgitant) valve. sten- narrow · -osis condition · re- back · gurgit- flood Taught in The cardiac cycle.
hemoglobin saturation (ok-SIM-eh-tree): The percentage of hemoglobin's oxygen-binding sites that are occupied, normally 95 to 100% in arterial blood. SaO2 is measured in an arterial blood sample; SpO2 is estimated by pulse oximetry, which shines red and infrared light through a finger. satur- full · oxi- oxygen · -metry measuring Taught in Oxygen transport.
Henry's law: The amount of a gas that dissolves in a liquid is proportional to that gas's partial pressure and its solubility. Carbon dioxide is about 20 times more soluble in plasma than oxygen. solu- loosen, dissolve Taught in Gas exchange.
hepatic portal system (heh-PAT-ik POR-tul): The route that carries blood from the capillaries of the stomach, intestines, spleen and pancreas through the hepatic portal vein to a second capillary bed, the liver's sinusoids, before it leaves through the hepatic veins to the inferior vena cava. hepat- liver · port- gate Taught in The major systemic veins.
homeostasis (hoh-mee-oh-STAY-sis): The maintenance of fairly stable conditions inside your body while conditions outside change. Each regulated variable moves within a normal range and is pulled back whenever it drifts. homeo- alike, same · -stasis standing still Taught in Homeostasis and feedback loops.
homeostasis (basic): Keeping internal conditions, such as body temperature and the water content of the blood, within a normal range even when the outside world changes. A change is detected and triggers a response that pushes the value back. Taught in Levels of organization and organ systems.
homeostatic imbalance: A state in which a regulated variable stays outside its normal range because some part of its feedback loop (sensor, control center, pathway or effector) has failed or been overwhelmed. Many diseases are failed regulation of this kind. Taught in Homeostasis and feedback loops.
hormone: A chemical messenger released into the blood that acts on target cells elsewhere in the body. It reaches nearly every cell, but only its target cells respond. horman to set in motion (Greek) Taught in Chemical messengers and receptors.
how blood carries carbon dioxide (kar-BAM-ih-noh-HEE-moh-gloh-bin): Blood carries carbon dioxide in three forms: about 70% as bicarbonate ions, about 20–23% as carbaminohemoglobin (carbon dioxide bound to the amino groups of globin, not the heme iron) and about 7–10% dissolved. carb- carbon · amino amino group · hem/o blood · globin the globular protein of hemoglobin Taught in Carbon dioxide transport.
how blood carries oxygen (OK-see-HEE-moh-gloh-bin): Blood carries about 98.5% of its oxygen bound to hemoglobin, four molecules per hemoglobin, and about 1.5% dissolved in plasma. Hemoglobin with oxygen bound is oxyhemoglobin; hemoglobin without it is deoxyhemoglobin. oxy- oxygen · de- removing · hemo- blood · -globin protein Taught in Oxygen transport.
hydrogen bond: A weak attraction between a partly positive hydrogen atom, covalently bonded to oxygen or nitrogen, and a partly negative oxygen or nitrogen atom nearby. No electrons are shared or transferred. hydr/o water · -gen producing Taught in Atoms, ions and chemical bonds.
hydrophilic and hydrophobic (hy-dro-FIL-ik; hy-dro-FO-bik): Hydrophilic (water soluble) substances are ions and polar molecules, which attract water and dissolve. Hydrophobic substances are nonpolar and are pushed into clusters by water molecules bonding with each other. hydr/o water · -philic loving · -phobic fearing Taught in Water, solutions and concentration.
hydrostatic pressure (hy-droh-STAT-ik): The pressure a fluid exerts, for example on the walls of its container. In a column of fluid it rises with depth, by about 0.74 mm Hg for each centimeter of water. hydro- water · stat- standing Taught in Gradients, pressure and flow.
hypertension (hy-per-TEN-shun): Arterial blood pressure that stays above normal on repeated measurements; by the American ACC/AHA guidelines (set in 2017 and kept in 2025), 130/80 mm Hg or more (stage 2 at 140/90 or more). Also called high blood pressure, it usually causes no symptoms but thickens the left ventricle and damages arteries over years. hyper- above, excessive · tens- stretched, pressure · -ion condition Taught in Hypertension, heart failure and shock.
hyperventilation and hypoventilation (hy-per-KAP-nee-uh): Hyperventilation is breathing more than carbon dioxide production requires, so arterial PCO2 falls below 35 mmHg (hypocapnia). Hypoventilation is breathing less, so PCO2 rises above 45 mmHg (hypercapnia). Both are defined by PCO2, not breathing rate. hyper- over, above · hypo- under, below · kapn- smoke, carbon dioxide Taught in Control of breathing.
hypothalamus (hy-poh-THAL-uh-mus): A small region of the diencephalon below and in front of the thalamus, just above the pituitary gland. Its nuclei act as control centers for many homeostatic loops. hypo- below · thalamus inner chamber Taught in Regions of the brain.
hypoxia (types) (hy-POK-see-uh): Too little oxygen reaching the tissues, or reaching them and not being used. Its four types are hypoxemic (low arterial PO2), anemic (low oxygen content), stagnant or circulatory (too little blood flow) and histotoxic (cells unable to use oxygen, as with cyanide). hypo- under · ox- oxygen · -ia condition · histo- tissue · toxic poison Taught in Oxygen transport.
inflammation (basic): The response of tissue to injury: chemical messengers such as histamine from mast cells dilate small arteries and make small vessels leaky, causing redness, heat, swelling and pain, and white blood cells move in to clear debris. inflamm/o to set on fire · -ation process Taught in Body membranes and tissue repair.
inorganic and organic compounds: An organic compound contains carbon covalently bonded to hydrogen; an inorganic compound, such as water, sodium chloride or carbon dioxide, does not. Functional groups are small clusters of atoms, such as hydroxyl, carboxyl, amino and phosphate, that give organic molecules predictable behavior. in- not · organ/o organ, living body Taught in Atoms, ions and chemical bonds.
inspiration: Breathing in (inhalation). In quiet breathing, the diaphragm and external intercostals contract and enlarge the thorax; intrapleural pressure falls, the lungs expand, alveolar pressure falls below atmospheric, and air flows in. Forced inspiration adds accessory muscles such as the scalenes, sternocleidomastoid and pectoralis minor. in- in · spir- to breathe Taught in Pulmonary ventilation.
intercalated disc (in-TER-kuh-lay-ted): The zigzag joint where two cardiac muscle fibers meet end to end. Its desmosomes hold the fibers together and its gap junctions let the electrical change pass from fiber to fiber. inter- between · calat- inserted Taught in Muscle tissue types.
internal respiration: Gas exchange between blood in systemic capillaries and the tissue cells: oxygen diffuses into the cells and carbon dioxide diffuses into the blood. It is not the same as cellular respiration, which uses the oxygen. intern- inside Taught in Gas exchange.
intracellular and extracellular fluid (in-ter-STISH-ul): Intracellular fluid (ICF) is the fluid inside cells. Extracellular fluid (ECF) is all fluid outside cells; its main parts are interstitial fluid, which bathes the cells, and plasma. intra- within · extra- outside · inter- between · -stitial standing Taught in The cell and its plasma membrane.
intracellular receptors: A receptor protein in the cytosol or nucleus (a nuclear receptor) that binds a lipid-soluble messenger. The pair binds DNA and switches genes on or off, so the response starts in hours and lasts hours to days. intra- within Taught in Chemical messengers and receptors.
intrinsic pacemaker rates (ek-TOP-ik): The rate each part of the conduction system fires at when left on its own: SA node about 60 to 100 per minute (about 100 with no nerve input), AV node and AV bundle about 40 to 60, bundle branches and Purkinje fibers about 20 to 40. Any site other than the SA node that sets the rhythm is an ectopic pacemaker, or ectopic focus. intrinsic from within · ec- out of · top- place Taught in The conduction system and pacemaker cells.
ion (EYE-on; KAT-eye-on; AN-eye-on): An atom or group of atoms with unequal numbers of protons and electrons, so it carries a net charge. A cation has lost electrons and is positive; an anion has gained electrons and is negative. The hydrogen ion, H+, is a lone proton. ion going · cat- down · an- up Taught in Atoms, ions and chemical bonds.
ion channel (EYE-on): An integral membrane protein that forms a water-filled tunnel through which one kind of ion passes quickly, down its electrochemical gradient. Leak channels are open most of the time; gated channels open and close in response to a trigger. ion going Taught in Passive transport across membranes.
ion differences across the membrane: The different ion contents of the fluids on each side of the plasma membrane: extracellular fluid is high in sodium and chloride, and intracellular fluid is high in potassium. Taught in The cell and its plasma membrane.
ionic bond: The electrical attraction between a positive ion and a negative ion, formed after one atom transfers electrons to another. Strong in a dry crystal, weak in water, which separates the ions. Taught in Atoms, ions and chemical bonds.
ionotropic and metabotropic receptors (eye-ON-oh-TROH-pik; meh-TAB-oh-TROH-pik): The two classes of receptor protein for neurotransmitters. An ionotropic receptor protein is a ligand-gated channel: fast and brief. A metabotropic receptor protein acts through a G protein and often a second messenger: slower, longer-lasting and amplified. iono- ion · trop- turning, acting on · metabo- change Taught in Synapses and neurotransmitters.
ipsilateral and contralateral (ip-sih-LAT-er-ul): Ipsilateral means on the same side of the body; contralateral means on the opposite side. The right arm and right leg are ipsilateral. ipse (Latin) same · contra- opposite · latus (Latin) side Taught in Anatomical position and directional terms.
L-type calcium channels: Voltage-gated calcium channels in the sarcolemma and T tubules of cardiac muscle cells that open slowly on depolarization and stay open a long time. The calcium entering through them holds the plateau and triggers calcium release from the sarcoplasmic reticulum. L long-lasting Taught in Cardiac muscle cells and their action potential.
language areas (BROH-kuhz; VER-nih-kuhz; uh-FAY-zhuh): Broca's area in the lower left frontal lobe (producing fluent, grammatical speech) and Wernicke's area in the upper left temporal lobe (understanding language), joined by a band of white matter. Damage causes aphasia: expressive (Broca's), receptive (Wernicke's) or conduction aphasia. a- without · phasis speech Taught in Cortical functions, memory, language and sleep.
larynx (LAIR-inks; KRY-koyd; ep-ih-GLOT-iss): The voice box: a cartilage tube between the laryngopharynx and the trachea that keeps the airway open, seals it during swallowing and makes sound. Its framework includes the thyroid cartilage (with the laryngeal prominence, or Adam's apple), the ring-shaped cricoid cartilage and the epiglottis. Inside, the vocal folds (true vocal cords) vibrate to make sound; the glottis is the vocal folds and the gap between them; the vestibular folds above do not make sound. larynx upper windpipe · thyr- shield · -oid like · cric- ring · epi- upon · glottis opening between the vocal folds · vestibul- entrance hall Taught in Nose, pharynx and larynx.
layers of a vessel wall (TOO-nih-kuh IN-tih-muh; VAY-suh vay-SOR-um): The three layers of a blood vessel wall: the tunica intima (endothelium on a basement membrane; in arteries, bounded by the internal elastic membrane), the tunica media (smooth muscle and elastic fibers; in arteries, bounded by the external elastic membrane) and the tunica externa, also called tunica adventitia (collagen). Large vessels carry their own small vessels and nerves, the vasa vasorum and nervi vasorum. tunica coat · intima innermost · media middle · externa outer · vasa vasorum vessels of the vessels Taught in Structure of blood vessels.
layers of the heart wall (ep-ih-KAR-dee-um, my-oh-KAR-dee-um, en-doh-KAR-dee-um): The three layers of the heart wall: the epicardium on the outside (the same layer as the visceral pericardium), the thick myocardium of cardiac muscle in the middle, and the endocardium, an endothelial lining, on the inside. epi- upon · my/o muscle · endo- within · cardi/o heart Taught in Heart location, coverings, chambers and great vessels.
ligand (LIG-und): Any molecule that binds specifically to a site on a protein. A chemical messenger is a ligand for its receptor protein, and so is a drug that binds the same site. ligare to bind (Latin) Taught in Chemical messengers and receptors.
limbic system (LIM-bik; hip-oh-KAM-pus; uh-MIG-duh-luh): A ring of structures at the inner border of the cerebrum, including the hippocampus, amygdala and cingulate gyrus (the limbic lobe), linked to the hypothalamus. It links emotion, memory and the body's responses to them. limbus border · hippocampus seahorse · amygdala almond Taught in Regions of the brain.
lipid (LIP-id): A molecule made mostly of carbon and hydrogen with few oxygen atoms, so it is nonpolar and does not dissolve in water. Fats, phospholipids and steroids are lipids; a substance that dissolves in them is lipid soluble. lip/o fat Taught in Carbohydrates, lipids, proteins and nucleic acids.
lobes of the cerebrum (puh-RY-uh-tul; ok-SIP-ih-tul; IN-suh-luh): The divisions of each cerebral hemisphere: frontal, parietal, temporal and occipital lobes, named for the skull bones over them, plus the insula buried in the lateral sulcus. The central sulcus separates frontal from parietal, the lateral sulcus lies above the temporal lobe, and the parieto-occipital sulcus separates parietal from occipital. pariet- wall · tempor- temple · occipit- back of the head · insula island Taught in Regions of the brain.
local autoregulation of blood flow: A tissue's ability to adjust its own blood flow by changing the radius of its arterioles, without nerves or hormones. Metabolic autoregulation dilates arterioles when metabolites build up; the myogenic response constricts them when pressure stretches them. auto- self · my/o muscle · -genic produced by Taught in Short-term blood pressure regulation.
location of the heart: Your heart sits in the mediastinum, between the lungs, behind the sternum and on the diaphragm, with about two thirds of its mass left of the midline. Its apex is the pointed lower tip, at about the fifth intercostal space on the left; its base is the broad upper, back end where the large vessels attach. apex tip · inter- between · cost/o rib Taught in Heart location, coverings, chambers and great vessels.
loose connective tissue (uh-REE-oh-lar; AD-ih-pose): Connective tissue with few, loosely woven fibers and plenty of ground substance. Its forms are areolar tissue (packing under epithelia), adipose tissue (fat cells, called adipocytes; brown fat makes heat) and reticular tissue (nets in soft organs). areola small open space · adip- fat Taught in Connective tissue.
lung compliance: Lung compliance is the change in lung volume per change in transpulmonary pressure (ΔV ÷ ΔP): how easily the lungs stretch. It is set by elastic fibers and by the surface tension of the fluid lining the alveoli, which surfactant lowers, so surfactant raises compliance. Thoracic wall compliance is how easily the chest wall expands. compli- to fill up, yield Taught in Pulmonary ventilation.
lungs (gross anatomy) (HY-lum): The paired, spongy organs of gas exchange on either side of the mediastinum. Each has an apex, a base on the diaphragm and a hilum where the bronchus, vessels and nerves enter. Fissures divide the right lung into three lobes and the left into two; the left has a cardiac notch for the heart. hilum small mark · fissura cleft · lobus rounded part Taught in Trachea, bronchial tree, alveoli and lungs.
lysosome (LY-soh-sohm): A membrane sac of digestive enzymes that work in acid. It digests material taken into the cell and recycles worn-out parts (autophagy); if lysosomes burst, the cell digests itself (autolysis). lysis breaking apart · -some body · auto- self · -phagy eating Taught in Organelles and the cytoskeleton.
macrophage (basic) (MAK-roh-fayj): A large cell in connective tissue that engulfs bacteria, dead cells and debris by phagocytosis and digests them. Any cell that eats this way is a phagocyte. macro- large · phag- eat · -cyte cell Taught in Connective tissue.
major named nerves (sy-AT-ik): The major nerves that leave the plexuses: phrenic (diaphragm), axillary (deltoid), radial (arm and forearm extensors), median (most forearm flexors and the thumb), ulnar (small hand muscles), femoral (quadriceps), sciatic (back of the thigh), dividing into the tibial and fibular nerves, plus the intercostal nerves between the ribs. Sciatica is pain along the sciatic nerve's path, usually from a compressed lower lumbar or sacral root. phren- diaphragm · cost- rib Taught in Spinal nerves and plexuses.
major neurotransmitters: The main neurotransmitters, grouped by chemistry: acetylcholine; amino acids (glutamate, the main excitatory one, and GABA and glycine, the main inhibitory ones); biogenic amines (norepinephrine, dopamine, serotonin); neuropeptides such as endorphins; and gases such as nitric oxide. bio- life · -genic produced by · endo- within Taught in Synapses and neurotransmitters.
mass balance: The rule that the amount of a substance in your body stays constant only when input (intake plus production) equals output (excretion plus use). If input exceeds output, the amount rises; if output exceeds input, it falls. Taught in Homeostasis and feedback loops.
mean arterial pressure: The average pressure in the arteries over a whole cardiac cycle, which drives blood through the organs. At rest it is estimated as diastolic pressure plus one-third of the pulse pressure; the estimate runs low at fast heart rates. Taught in Blood pressure, flow and resistance.
mean arterial pressure equals cardiac output times resistance: The rule MAP = CO × TPR: mean arterial pressure equals cardiac output times total peripheral resistance. Because CO = heart rate × stroke volume, blood pressure can change only through heart rate, stroke volume or resistance. Taught in Short-term blood pressure regulation.
measuring blood pressure (sfig-moh-muh-NOM-ih-ter; kuh-ROT-kof): Measuring arterial pressure with a sphygmomanometer: a cuff squeezes the brachial artery shut and is slowly let down. The first Korotkoff sound marks systolic pressure and the last marks diastolic pressure. A cuff that is too small or an arm below heart level gives a reading that is too high. sphygmo- pulse · mano- thin · -meter measure Taught in Blood pressure, flow and resistance.
medial and lateral: Medial means closer to the midline that divides the body into equal right and left halves; lateral means farther from it, toward the side. Intermediate means between a more medial and a more lateral structure. medius (Latin) middle · latus (Latin) side Taught in Anatomical position and directional terms.
mediastinum (mee-dee-uh-STY-num): The central compartment of the thoracic cavity, between the two lungs, from the breastbone to the backbone and from the neck to the diaphragm. It holds the heart, the large vessels, the trachea, the esophagus and the thymus. mediastinus (Latin) standing in the middle Taught in Body cavities and serous membranes.
medical imaging: Ways of making pictures of the inside of a living body without opening it. A radiograph (X-ray) is a flat projection; CT, MRI, PET and ultrasound produce sections. tom/o cut, slice · -graphy recording · son/o sound Taught in Body planes and sections.
membrane potential: The voltage across a cell's plasma membrane, always read as the inside compared with the outside. A value of −70 mV means the inside is 70 millivolts more negative than the outside. potentia power (Latin); a stored ability to push charge Taught in The resting membrane potential.
membrane proteins: Proteins in or on a membrane. Integral proteins are embedded in the bilayer, most spanning it; peripheral proteins sit loosely on one surface. They transport substances, act as enzymes, bind signals, anchor the cell and mark its identity. integer whole · peri- around Taught in The cell and its plasma membrane.
membrane receptors and second messengers: A small molecule made inside a cell that carries the signal of a first messenger bound outside. In the usual arrangement, a G-protein-coupled receptor switches on a G protein, which switches on a membrane enzyme that turns ATP into cyclic AMP (cAMP). Taught in Chemical messengers and receptors.
memory (neural) (am-NEE-zhuh): The storing and recall of information. Short-term and working memory hold a few items briefly; long-term memory is declarative (episodic and factual) or procedural (skills). The hippocampus consolidates new declarative memories into the cortex by strengthening synapses. Anterograde amnesia is loss of new memory formation; retrograde amnesia is loss of memories from before an injury. antero- forward · retro- backward · a- without · mnesis memory · con- together · solidus firm Taught in Cortical functions, memory, language and sleep.
meninges (meh-NIN-jeez; DOO-ruh MAY-ter; uh-RAK-noyd; PEE-uh): The three membranes around the brain and spinal cord: the tough dura mater outside, the web-like arachnoid mater, and the thin pia mater on the nervous tissue. The epidural space lies outside the dura, the subdural space between dura and arachnoid, and the CSF-filled subarachnoid space between arachnoid and pia. meninx membrane · dura tough · mater mother · arachn- spider · pia tender · epi- upon · sub- under Taught in Meninges, ventricles and cerebrospinal fluid.
mesenchyme (MEZ-en-kime): Loose embryonic connective tissue of star-shaped mesenchymal cells in a watery ground substance. These stem cells give rise to fibroblasts, fat cells, chondrocytes and the cells that build bone. mes- middle · -enchyme poured-in tissue Taught in Connective tissue.
metabolism (anabolism and catabolism) (meh-TAB-oh-lizm, kuh-TAB-oh-lizm, uh-NAB-oh-lizm): All the chemical reactions in your body. Catabolism breaks large molecules into smaller ones and usually releases energy; anabolism builds large molecules from smaller ones and usually needs energy. metabol- change · -ism process · cata- down · ana- up Taught in Energy, metabolism and enzymes.
microvilli (my-kroh-VIL-eye): Tiny, nonmoving, finger-like folds of the plasma membrane with a core of actin that increase surface area for absorption. A dense layer of them forms a brush border. micro- small Taught in Organelles and the cytoskeleton.
minute ventilation: The total volume of air moved into or out of the lungs each minute: tidal volume times respiratory rate, about 6 L/min at rest. The respiratory rate is the number of breaths per minute, 12 to 20 in a resting adult. ventil- fan, move air Taught in Lung volumes and ventilation rates.
mitochondrion (my-toh-KON-dree-on): A bean-shaped organelle with a smooth outer membrane and a folded inner membrane that uses oxygen to oxidize fuel molecules and captures the released energy as ATP. mito- thread · chondrion granule Taught in Organelles and the cytoskeleton.
mitosis (my-TOH-sis): Division of the nucleus of a somatic cell into two nuclei with identical chromosome sets, in four phases: prophase, metaphase (chromosomes on the metaphase plate), anaphase (sister chromatids pulled apart by the mitotic spindle via their kinetochores) and telophase. mit- thread · -osis process · somat- body · pro- before · meta- middle · ana- apart · telo- end Taught in Cell division and differentiation.
modes of secretion (MER-oh-krin, AP-oh-krin, HOL-oh-krin): The three ways an exocrine cell releases its product: merocrine (by exocytosis; the cell stays whole), apocrine (the product-filled apical end pinches off) and holocrine (the whole cell breaks apart and becomes the secretion). mero- part · apo- off, away from · holo- whole Taught in Glands: endocrine and exocrine.
monomers and polymers (MON-o-mer; POL-ih-mer; hy-DROL-ih-sis): A monomer is a small unit that can link to others like it; a polymer is a chain of many monomers joined by covalent bonds, and a macromolecule is any very large molecule. Dehydration synthesis joins monomers and releases water; hydrolysis adds water and splits them apart. mono- one · poly- many · -mer part · macro- large · hydr/o water · -lysis splitting Taught in Carbohydrates, lipids, proteins and nucleic acids.
mucous membrane (myoo-KOH-sah; LAM-ih-nah PROH-pree-ah): An epithelial membrane (mucosa) lining a tract that opens to the outside of the body, such as the digestive and respiratory tracts. Its epithelium rests on the lamina propria, a layer of loose connective tissue, and in most places it is coated with mucus. muc/o mucus · lamina thin layer · propria its own Taught in Body membranes and tissue repair.
muscle fiber (MY-oh-site): A single muscle cell, also called a myocyte. It is a whole living cell, unlike the nonliving protein fibers of connective tissue. my-, myo- muscle · -cyte cell Taught in Muscle tissue types.
muscle tissue: The primary tissue type made of muscle cells, which contract, shortening with force by using myosin to pull on actin filaments. It comes in three kinds: skeletal, cardiac and smooth. mus- little mouse (the shape of a flexing muscle) Taught in Muscle tissue types.
mutation (myoo-TAY-shun): A lasting change in the base sequence of DNA. Depending on how it alters the codons, it can leave the protein unchanged (silent), swap one amino acid (missense), end the protein early (nonsense) or shift the reading frame. mut- change Taught in From gene to protein.
myelin sheath (MY-eh-lin; RAHN-vee-ay): Many tightly wrapped layers of a glial cell's plasma membrane around an axon segment, mostly lipid, which insulate it and speed signals along it. The bare gaps between segments are nodes of Ranvier; axons with this wrapping are myelinated, those without it unmyelinated. myel- marrow Taught in Neurons and glial cells.
myocardial ischemia and infarction (is-KEE-mee-uh; in-FARK-shun; an-JY-nuh): Myocardial ischemia is blood flow to heart muscle too low for its oxygen demand; when it reverses it causes angina. A myocardial infarction (heart attack) is death of heart muscle from ischemia that lasts too long, usually a clot on a cracked fatty plaque. isch- hold back · -emia blood condition · my/o muscle · cardi/o heart · infarct stuffed in · angina strangling Taught in Blood flow through the heart and the two circuits.
necrosis (neh-KROH-sis): Cell death caused by injury, such as lost blood supply, crushing, burns or poisons. The cells swell and burst, and their spilled contents trigger inflammation. necr/o death · -osis condition Taught in Body membranes and tissue repair.
negative feedback: A loop in which the response opposes the stimulus, moving the regulated variable back toward the set point; the loop switches itself off as the change shrinks. Most homeostatic loops work this way. Taught in Homeostasis and feedback loops.
nerve: A cable of many axons, bundled with connective tissue and blood vessels, that runs outside the brain and spinal cord. It usually carries signals in both directions, in different axons. Taught in Nervous tissue.
nerve plexuses (PLEK-sus): Networks where the ventral rami of neighboring spinal nerves branch, join and exchange axons before giving off named nerves: the cervical (C1–C4), brachial (C5–T1), lumbar (L1–L4) and sacral (L4–S4) plexuses. plexus braid · brachi- arm · lumb- loin, lower back Taught in Spinal nerves and plexuses.
nervous versus endocrine signaling: The two long-distance messaging systems. Nervous signaling sends action potentials along axons and a neurotransmitter across a synapse to one cell, acting in milliseconds; endocrine signaling sends a hormone through the blood to every target cell, acting in seconds to hours and lasting longer. endo- within · krinein to separate or release (Greek) Taught in Chemical messengers and receptors.
net filtration pressure in capillaries: The sum of the four Starling forces across a capillary wall: NFP = (CHP + IFCOP) − (BCOP + IFHP). A positive value means capillary filtration, fluid moving out; a negative value means capillary reabsorption, fluid moving in. filtr- strain through felt Taught in Capillary exchange.
neural circuits: Patterns of connection among neurons. In divergence one neuron synapses on many, spreading its signal; in convergence many neurons synapse on one, which sums their inputs. di- apart · con- together · vergere to turn, incline (Latin) Taught in Synapses and neurotransmitters.
neuron (NOOR-on): A cell of nervous tissue that receives signals, combines them and sends a signal of its own to other cells; also called a nerve cell. Mature neurons do not divide. neur- nerve Taught in Nervous tissue.
neuron structure in detail (SOH-mah; AK-soh-plaz-um): The soma (cell body) holds the nucleus and Nissl bodies (rough ER); the axon hillock is where the axon leaves it; the initial segment just beyond is the trigger zone, where action potentials start; the axon's cytoplasm is axoplasm, and its side branches are axon collaterals. soma body · hillock small hill · -plasm formed substance · later- side Taught in Neurons and glial cells.
neurotransmitter: A chemical messenger that a neuron releases from its axon terminal at a synapse. It crosses the synaptic cleft and binds receptor proteins on the postsynaptic cell; it is cleared within milliseconds. neuro- nerve · trans- across · mittere to send (Latin) Taught in Chemical messengers and receptors.
normal blood pH: 7.35 to 7.45 in blood from an artery, a hydrogen ion concentration of about 35 to 45 nmol/L. Blood is slightly basic. Taught in Acids, bases, pH and buffers.
normal partial pressures: Typical partial pressures at rest at sea level: alveolar air PO2 about 100 and PCO2 about 40 mm Hg; arterial blood PO2 about 95 (80 to 100) and PCO2 40 (35 to 45); venous blood PO2 about 40 and PCO2 about 46 mm Hg. Taught in Gas exchange.
nose and nasal cavity (NAIR-eez; NAIR-iss): The external nose is the part of the nose on the face, supported by bone above and cartilage below; air enters it through the two nares (nostrils). Behind them, the nasal cavity is the air space divided by the nasal septum, floored by the roof of the mouth, roofed by the cribriform plate and walled by the conchae. Its blood-rich, mucus-covered lining filters, warms and humidifies air. nas- nose · naris nostril · septum partition · concha shell Taught in Nose, pharynx and larynx.
nucleic acid (noo-KLAY-ik; PYOOR-een; pih-RIM-ih-deen): A polymer of nucleotides, each a phosphate, a five-carbon sugar and a nitrogenous base. Deoxyribonucleic acid stores hereditary instructions and ribonucleic acid carries them out; purines (A, G) have two rings and pyrimidines (C, T, U) have one. nucle/o kernel, nucleus · de- without · oxy- oxygen Taught in Carbohydrates, lipids, proteins and nucleic acids.
nucleus (of a cell) (NOO-klee-us): The organelle that holds a cell's DNA. A double-membrane nuclear envelope with nuclear pores surrounds it, and a dense nucleolus inside it assembles ribosome parts. nucle- kernel · -olus little (in nucleolus) Taught in The nucleus, DNA and genes.
organ: A structure made of two or more kinds of tissue that has a recognizable shape and does a specific job, such as the stomach or a kidney. organon (Greek) tool Taught in Levels of organization and organ systems.
organ system: A group of organs that work together on a shared job, such as the digestive system. Taught in Levels of organization and organ systems.
organelle (or-guh-NEL): A structure in the cytoplasm with a specific job; most are wrapped in their own membrane. The cytosol is the fluid part of the cytoplasm in which the organelles sit. organ organ · -elle little · -sol solution Taught in Organelles and the cytoskeleton.
organism: A whole living individual. In humans, all eleven organ systems working together make the organism. Taught in Levels of organization and organ systems.
orthostatic hypotension (or-thoh-STAT-ik HY-poh-TEN-shun): A sustained fall in blood pressure on standing: at least 20 mm Hg systolic or 10 mm Hg diastolic within 3 minutes. Also called postural hypotension, it causes lightheadedness or fainting when the baroreceptor reflex cannot keep up. orth/o straight, upright · stat- standing · hypo- below · tens- stretched, pressure Taught in Short-term blood pressure regulation.
osmolarity (oz-mo-LAR-ih-tee): The total concentration of all dissolved particles in a solution, counting each ion separately, in milliosmoles per liter (mOsm/L). Osmolality is the same count per kilogram of water (mOsm/kg); normal blood osmolality is about 275 to 295 mOsm/kg. osm/o push Taught in Water, solutions and concentration.
osmosis (oz-MOH-sis): The net movement of water across a semipermeable membrane from the side with fewer dissolved particles to the side with more (from lower to higher osmolarity). Only particles the membrane holds back count: water follows solute. osmos a push · -osis process Taught in Diffusion and osmosis.
osmotic pressure (oz-MOT-ik): The pressure needed to stop water moving into a solution by osmosis. It rises with the number of dissolved particles the membrane holds back, by about 19 mm Hg for each mOsm/L at body temperature, and water moves toward the side where it is higher. osmos a push Taught in Diffusion and osmosis.
other inputs to breathing (HAIR-ing BROY-er): Inputs besides the chemoreceptors that change breathing: lung stretch receptors (the Hering–Breuer reflex, which limits inflation), irritant receptors in the airways (cough, bronchoconstriction), proprioceptors, the cerebral cortex (voluntary control) and the hypothalamus and limbic system (emotion, pain, temperature). Taught in Control of breathing.
oxidation and reduction (REE-doks): Oxidation is the loss of electrons and reduction is the gain of electrons; they always happen together in an oxidation-reduction reaction. Electron carriers such as NAD+ (which becomes NADH) and FAD pick up electrons in one reaction and deliver them in another. red- back · -ox from oxygen Taught in Energy, metabolism and enzymes.
oxygen–hemoglobin dissociation curve: The S-shaped graph of hemoglobin saturation against PO2. Cooperative binding, where each oxygen that binds makes the other sites bind more readily, makes it flat above about 60 mm Hg and steep below about 50. Hemoglobin is 50% saturated at about 27 mm Hg (the P50). dis- apart · soci- join · co- together · oper- work Taught in Oxygen transport.
oxygenated and deoxygenated blood: Oxygenated (oxygen-rich) blood has just left the lungs, with its hemoglobin about 97 to 98 percent loaded with oxygen. Deoxygenated (oxygen-poor) blood has passed through the tissues and given up some oxygen, but at rest it is still about 75 percent loaded; both are red. oxy- oxygen · de- removed Taught in Blood flow through the heart and the two circuits.
pacemaker potential: The slow, spontaneous depolarization of an autorhythmic cell between action potentials, also called the prepotential. It is driven by the funny current (Na⁺ in through HCN channels), falling K⁺ exit, and late T-type Ca²⁺ entry; its slope sets how often the cell fires. pre- before Taught in The conduction system and pacemaker cells.
paracrine and autocrine signaling (pair-uh-KRIN, AW-toh-krin): Local signaling. In paracrine signaling a messenger, such as nitric oxide, diffuses to neighboring cells; in autocrine signaling it binds receptor proteins on the same cell that released it. Cytokines, including interleukins, are small proteins used this way. para- beside · auto- self · krinein to separate or release (Greek) · cyto- cell Taught in Chemical messengers and receptors.
partial pressure: The pressure one gas in a mixture exerts: the total pressure times that gas's fraction of the mixture, written PO2 for oxygen and PCO2 for carbon dioxide. By Dalton's law, the partial pressures add up to the total pressure. parti- part Taught in Gas exchange.
parts of the aorta (ay-OR-tuh; hy-AY-tus): The named sections of the aorta: the ascending aorta rising from the left ventricle, the aortic arch curving over to the left, and the descending aorta, which is the thoracic aorta in the chest and, after it passes through the aortic hiatus of the diaphragm, the abdominal aorta. aort- lifted up · thorac- chest · hiat- gap Taught in The major systemic arteries.
passive transport: Movement of a substance across a membrane down its gradient, powered by the gradient itself, with no ATP spent by the cell. Simple diffusion, facilitated diffusion, osmosis and filtration are all passive transport. passivus not acting Taught in Passive transport across membranes.
path of blood through the heart: The order blood takes: venae cavae, right atrium, tricuspid valve, right ventricle, pulmonary valve, pulmonary trunk and arteries, lungs, pulmonary veins, left atrium, mitral valve, left ventricle, aortic valve, aorta, body. Taught in Blood flow through the heart and the two circuits.
pericardial cavity (pair-ih-KAR-dee-ul): The thin, fluid-filled space around the heart, between the serous layer on the heart's surface and the outer layer of the sac that encloses it. It lies in the mediastinum. peri- around · cardi/o heart Taught in Body cavities and serous membranes.
pericardium (layers) (pair-ih-KAR-dee-um): The covering around the heart: a tough outer fibrous pericardium of dense connective tissue, and an inner serous pericardium folded into a parietal layer and a visceral layer with a film of serous fluid (the pericardial cavity) between them. The fibrous layer plus the parietal layer form the pericardial sac. peri- around · cardi/o heart · pariet- wall · viscer- internal organ · ser/o watery fluid Taught in Heart location, coverings, chambers and great vessels.
peripheral chemoreceptors (kuh-ROT-id): Sensory cells in the carotid bodies (at the fork of each common carotid artery) and the aortic bodies (on the aortic arch) that respond to low arterial PO2, high PCO2 and low pH, and signal the medulla through the glossopharyngeal and vagus nerves. peri- around · pher- carry Taught in Control of breathing.
peritoneal cavity (pair-ih-toh-NEE-ul): The thin, fluid-filled space in the abdominopelvic cavity between the layer of peritoneum lining the abdominal wall and the layer covering the organs. The peritoneum is the largest serous membrane in the body. peritonaion (Greek) stretched around Taught in Body cavities and serous membranes.
peroxisome (per-OK-sih-sohm): A small membrane sac of oxidizing enzymes that breaks down very long fatty acids and some toxins. Catalase inside it destroys the hydrogen peroxide these reactions make. Hydrogen peroxide is a reactive oxygen species; free radicals are reactive molecules with an unpaired electron. peroxi- from hydrogen peroxide · -some body Taught in Organelles and the cytoskeleton.
pH (pee-AITCH): A number for the hydrogen ion concentration of a fluid: the negative log of [H+] in mol/L. pH 7 is neutral, below 7 is acidic and above 7 is basic; each whole unit is a tenfold change in H+. p power (of ten) · H hydrogen Taught in Acids, bases, pH and buffers.
pharynx (FAIR-inks; nay-zoh-FAIR-inks; lah-RING-go-FAIR-inks): The muscular throat tube from the back of the nasal cavity to the esophagus. The nasopharynx (behind the nose) carries only air and holds the pharyngeal tonsil and the auditory tube openings; the oropharynx (behind the mouth) and laryngopharynx (behind the larynx) carry air and food and are lined by stratified squamous epithelium. pharynx throat · naso- nose · oro- mouth · laryngo- larynx Taught in Nose, pharynx and larynx.
phases of the cardiac cycle (eye-soh-vol-yoo-MET-rik): The five phases of each heartbeat: ventricular filling, atrial contraction (atrial systole), isovolumetric contraction (both valves closed, pressure rising), ventricular ejection, and isovolumetric relaxation (both valves closed, pressure falling). Isovolumic is another name for isovolumetric. iso- equal · volum- volume · -metric measure Taught in The cardiac cycle.
phases of the neuron action potential: The stages of a neuron action potential: rest at about −70 mV, depolarization to threshold at about −55 mV, a rising phase to about +30 mV as sodium enters, a falling phase as potassium leaves, and an afterhyperpolarization to about −80 mV before the membrane returns to rest. hyper- above, beyond Taught in The action potential in detail.
phospholipid (fos-fo-LIP-id; am-fih-PATH-ik): A lipid with two fatty acid tails and a charged, phosphate-containing head. It is amphipathic, with a hydrophilic head and hydrophobic tails, so in water it forms a two-layer sheet: the basic structure of the boundary around every cell. phosph/o phosphorus · lip/o fat · amphi- both · -pathic feeling Taught in Carbohydrates, lipids, proteins and nucleic acids.
phospholipid bilayer: Two sheets of phospholipids arranged tail to tail, with hydrophilic heads facing the water on each side and hydrophobic tails forming an oily core. It is the basic structure of every cell membrane. phospho- phosphate · lip- fat · bi- two Taught in The cell and its plasma membrane.
physiology (fiz-ee-OL-uh-jee): The study of how the body's structures work: the chemical and physical events that make them do their jobs. physi/o nature · -logy study of Taught in Levels of organization and organ systems.
planes and sections: A plane is an imaginary flat surface passed through the body; a section is the cut surface produced when the body or an organ is divided along a plane. An oblique plane runs at an angle between the three main planes. planus (Latin) flat · sect- cut · obliquus (Latin) slanted Taught in Body planes and sections.
plasma (the fluid part of blood): The fluid part of blood: mostly water, with dissolved salts, nutrients, wastes and proteins. It is the part of the extracellular fluid that travels through blood vessels. plasma something formed or molded Taught in The cell and its plasma membrane.
plasma membrane: The thin outer boundary of a cell, also called the cell membrane: a phospholipid bilayer with proteins set into it. It controls what enters and leaves the cell. plasma something formed or molded Taught in The cell and its plasma membrane.
pleura (layers) (PLOOR-uh): The serous membrane around each lung: the visceral pleura covers the lung surface, the parietal pleura lines the chest wall, diaphragm and mediastinum, and they meet at the hilum. Between them, a film of pleural fluid lubricates the layers and holds the lung against the chest wall. pleura rib, side · viscer- internal organ · pariet- wall Taught in Trachea, bronchial tree, alveoli and lungs.
pleural cavity (PLOOR-ul): The thin, fluid-filled space around each lung, between the layer of pleura on the lung and the layer on the inside of the chest wall. There are two, right and left, separated by the mediastinum. pleura (Greek) side, rib Taught in Body cavities and serous membranes.
pneumothorax (noo-moh-THOR-aks): Air in a pleural cavity, from a chest wound or a leak from the lung. Intrapleural pressure rises toward atmospheric, transpulmonary pressure is lost and the lung on that side collapses. In a tension pneumothorax, trapped air builds pressure that compresses the other lung and the great veins. pneumo- air, lung · thorax chest Taught in Pulmonary ventilation.
polarity: An uneven spread of charge. A polar covalent bond shares electrons unequally, leaving partial charges; a nonpolar bond shares them evenly. A polar molecule has a partly positive and a partly negative end, which depends on both its bonds and its shape. pol/o pole, end Taught in Atoms, ions and chemical bonds.
positive feedback: A loop in which the response strengthens the stimulus, pushing the variable further in the same direction until an event outside the loop ends it, as in childbirth and blood clotting. Taught in Homeostasis and feedback loops.
potassium leak and the resting potential: At rest, many potassium leak channels are open. Potassium diffuses out through them and leaves trapped negative proteins behind, which makes the inside negative; this is the main source of the resting potential. Taught in The resting membrane potential.
prefix: A word part placed before a root that modifies its meaning, often telling where, how much, how many or how fast, such as tachy- (fast) in tachypnea. pre- before Taught in Medical word parts.
preload: The stretch on ventricular muscle at the end of filling, just before contraction, indexed by end-diastolic volume. It rises with greater venous return and with a longer filling time. pre- before Taught in Cardiac output and its control.
pressure (physics): Force per unit area. In physiology it is measured in millimeters of mercury (mm Hg) and usually given relative to atmospheric pressure, the pressure of the surrounding air (about 760 mm Hg at sea level). atmo- vapor · sphere ball Taught in Gradients, pressure and flow.
pressure along the vascular tree: The way blood pressure changes along the systemic circulation: high and pulsing in the arteries, falling most steeply across the arterioles, lower through the capillaries, and falling slowly to near zero in the veins and at the right atrium. Taught in Blood pressure, flow and resistance.
pressure gradient: A difference in pressure between two points, written ΔP. Fluids flow from higher toward lower pressure, and flow depends on the difference, not on how high the pressures are. grad- step Taught in Gradients, pressure and flow.
pressure–volume loop: A graph of left ventricular pressure against left ventricular volume over one beat. It traces a counterclockwise loop whose corners are the four valve events and whose width is the stroke volume. Taught in The cardiac cycle.
pressures in ventilation (in-truh-PLOOR-ul): Pulmonary ventilation is the movement of air into and out of the lungs, driven by pressure differences. Alveolar (intrapulmonary, intra-alveolar) pressure is the pressure inside the alveoli and returns to atmospheric whenever airflow stops. Intrapleural pressure, in the pleural fluid film, is about 4 mm Hg below atmospheric at rest. Transpulmonary pressure, alveolar minus intrapleural, holds the lungs open. pulmon- lung · ventil- to fan, air out · intra- within · trans- across Taught in Pulmonary ventilation.
primary active transport: Active transport in which the carrier, called a pump, splits ATP itself and uses the energy to move a substance against its gradient. The sodium–potassium pump and calcium pumps are examples. primus first Taught in Active transport and vesicles.
propagation: The travel of an action potential along a membrane. Charge from a firing patch depolarizes the next patch to threshold, so each patch regenerates a full-sized action potential; the refractory patch behind keeps it moving one way. propagare to extend, spread (Latin) Taught in Electrical signals: graded potentials and action potentials.
properties of muscle tissue: The four properties all muscle shares: responsiveness to signals, the ability to contract, extensibility (being stretched without damage) and elasticity (recoiling to resting length). ex- out · tend- stretch Taught in Muscle tissue types.
properties of water: The behaviors that follow from water's polarity and hydrogen bonds: it absorbs much heat with little warming, takes much heat to evaporate, clings to itself (cohesion and surface tension, the inward pull at a water surface), lubricates and cushions, takes part in reactions and dissolves many substances. Taught in Water, solutions and concentration.
protein (PRO-teen; pol-ee-PEP-tide): A polymer of amino acids folded into a working shape. Each amino acid has an amino group, a carboxyl group and a side chain; peptide bonds join them into a chain called a polypeptide. prote- first, primary · pept- digested · poly- many Taught in Carbohydrates, lipids, proteins and nucleic acids.
protein shape and denaturation (dee-nay-chur-AY-shun): A protein's structure: its amino acid sequence, local coils and sheets, overall fold and, in some, several chains fitted together, held by hydrogen bonds, ionic bonds and covalent disulfide bonds. Denaturation is the loss of that shape, and with it the protein's function, without breaking the peptide bonds. de- remove · di- two · sulf/o sulfur Taught in Carbohydrates, lipids, proteins and nucleic acids.
protons, neutrons and electrons: The three particles of an atom. Protons (positive) and neutrons (no charge) form the nucleus; electrons (negative, very light) occupy shells around it, and the outermost occupied shell is the valence shell. sub- below · prot/o first · neutr/o neither Taught in Atoms, ions and chemical bonds.
proximal and distal: Proximal means closer to where a limb attaches to the trunk, or to where a tube begins; distal means farther from that point. The elbow is proximal to the wrist. proximus (Latin) nearest · distare (Latin) to stand apart Taught in Anatomical position and directional terms.
pseudostratified ciliated columnar epithelium (SOO-doh-STRAT-ih-fyed): A single layer of columnar cells of different heights, so the nuclei sit at different levels and the sheet looks layered. The ciliated form with goblet cells lines the inside of the nose, the trachea and the larger airways. pseudo- false · strat- layer Taught in Epithelial tissue.
pulmonary circuit (PUL-muh-nair-ee): The loop that carries blood from the right ventricle through the pulmonary trunk and arteries to the pulmonary capillaries around the alveoli, where it picks up oxygen and gives off carbon dioxide, and back through the pulmonary veins to the left atrium. It works at low pressure. pulmon- lung Taught in Blood flow through the heart and the two circuits.
pulmonary edema (eh-DEE-muh): Fluid buildup in the lung tissue and then the alveoli, caused by high pressure in the pulmonary capillaries (as in left-sided heart failure) or by a leaky respiratory membrane (as in sepsis or pneumonia). It slows diffusion, stiffens the lungs and floods alveoli. pulmon- lung · oidema swelling Taught in Respiratory disorders.
pulse points: Places where an artery runs near the skin over firm tissue, so its pulse, the pressure wave from each heartbeat, can be felt: temporal, facial, carotid, brachial, radial, femoral, popliteal, posterior tibial and dorsalis pedis. puls- beat, push Taught in The major systemic arteries.
pulse pressure: Systolic pressure minus diastolic pressure: the size of each beat's pressure swing. It widens with a larger stroke volume or a stiffer aorta and narrows when stroke volume is small. puls- beat, push Taught in Blood pressure, flow and resistance.
RAAS in blood pressure control (an-jee-oh-TEN-sin): The role of the renin–angiotensin–aldosterone system in raising blood pressure: low pressure makes the kidneys release renin, leading to angiotensin II, which constricts arterioles, releases aldosterone so the kidneys keep sodium and water, and triggers ADH and thirst. angi/o vessel · tens- stretched, pressure Taught in Long-term blood pressure regulation.
radius and resistance (pwah-ZOY): Resistance depends on the fourth power of the radius (Poiseuille's law), so halving a tube's radius makes its resistance 16 times larger and its flow 16 times smaller at the same pressure gradient. Taught in Gradients, pressure and flow.
reaction rates, reversibility and equilibrium (ee-kwih-LIB-ree-um): The reaction rate is how fast reactants become products; more reactant, higher temperature or a catalyst raises it. A reversible reaction runs both ways, and at chemical equilibrium the forward and reverse rates are equal, so the amounts stop changing. In an exchange reaction, parts of two molecules trade places. equi- equal · libra balance · cata- down · -lyst loosen Taught in Energy, metabolism and enzymes.
receptor protein: A protein that binds a specific chemical messenger and, by changing shape, starts a response in the cell. Binding is specific and reversible, and the receptor protein, not the messenger, decides what the cell does. recipere to receive (Latin) Taught in Chemical messengers and receptors.
red cells, white cells and platelets (basic): The formed elements of blood. Red blood cells carry oxygen and lose their nucleus as they mature; white blood cells defend against infection; platelets are cell fragments that help seal breaks in blood vessels. Taught in The cell and its plasma membrane.
refractory period (ree-FRAK-tor-ee): A short time during and just after an action potential when the membrane cannot fire again, or fires only with a stronger stimulus, because its sodium channels cannot reopen until it repolarizes. refractarius stubborn (Latin) Taught in Electrical signals: graded potentials and action potentials.
regeneration of nerve fibers: Regrowth of a cut axon. In the PNS, the part beyond the cut breaks down, Schwann cells form a tube and the axon regrows along it at about 1 mm per day; in the CNS, missing guidance, growth-blocking myelin proteins and the astrocyte scar usually prevent regrowth. re- again · gener- produce Taught in Neurons and glial cells.
regional terms (seh-FAL-ik, KROO-rul): Names for areas of the body surface in the anatomical position, such as cephalic (head), cervical (neck), thoracic (chest), lumbar (lower back), brachial (arm, shoulder to elbow), antebrachial (forearm), femoral (thigh) and crural (leg, knee to ankle). kephale (Greek) head · brachium (Latin) arm · ante- before · crus (Latin) leg · lumbus (Latin) loin Taught in Body regions and abdominal quadrants.
regulated variable: A condition your body actively holds within a normal range, such as body temperature, blood pressure, blood pH or the level of glucose in the blood. Taught in Homeostasis and feedback loops.
resistance (to flow) (vis-KOS-ih-tee): Anything that opposes flow, caused by friction between the fluid and the tube wall and within the fluid. It rises with a narrower radius, a longer tube and higher viscosity, the thickness or internal friction of the fluid. viscos- sticky Taught in Gradients, pressure and flow.
respiratory capacities: Sums of two or more respiratory volumes: inspiratory capacity (TV + IRV), functional residual capacity (ERV + RV), vital capacity (TV + IRV + ERV) and total lung capacity (all four volumes). capac- able to hold · vita life Taught in Lung volumes and ventilation rates.
respiratory centers (noo-moh-TAK-sik; ap-NOO-stik): Groups of neurons in the medulla oblongata and pons that generate the respiratory rhythm and drive the breathing muscles: the ventral and dorsal respiratory groups in the medulla, and the pontine respiratory group (pneumotaxic center) and apneustic center in the pons. pneum- air, breath · tax- arrangement, order · a- without · pneus- breathing · ventr- belly side · dors- back Taught in Control of breathing.
respiratory infections (noo-MOH-nyuh; too-ber-kyoo-LOH-sis): Infection of the respiratory tract. Pneumonia is infection of the alveoli, which fill with inflammatory fluid; tuberculosis is airborne infection by Mycobacterium tuberculosis, which survives in alveolar macrophages, is walled off in granulomas, and can stay latent for years. pneumon- lung · -ia condition · tubercul- small swelling · -osis condition Taught in Respiratory disorders.
respiratory membrane: The barrier between alveolar air and capillary blood: a type I alveolar cell, the fused basement membranes and a capillary endothelial cell, about 0.5 µm thick in all. Its thinness and huge area let oxygen and carbon dioxide diffuse across quickly. re- again · spir- to breathe Taught in Trachea, bronchial tree, alveoli and lungs.
respiratory volumes: The four non-overlapping volumes that together fill the lungs: tidal volume (one quiet breath, about 500 mL), inspiratory reserve volume (extra air you can breathe in), expiratory reserve volume (extra air you can breathe out) and residual volume (air that can never be breathed out). tid- tide · re- back · serv- keep · residu- left behind Taught in Lung volumes and ventilation rates.
resting membrane potential: The membrane potential of a cell that is not being disturbed: about −70 mV in a typical neuron and about −90 mV in skeletal and heart muscle. It comes mainly from potassium leaking out of the cell. Taught in The resting membrane potential.
reticular formation (reh-TIK-yoo-lur): A net of neurons through the core of the brainstem. Its upward part, the reticular activating system, keeps the cerebral cortex awake and alert; it also filters repeated input and sets background muscle tension. reticulum little net Taught in Regions of the brain.
ribosome (RY-boh-sohm): A tiny particle of protein and nucleic acid, with no membrane, that builds proteins by linking amino acids. Free ribosomes make proteins for the cytosol; ribosomes on the rough ER make proteins for membranes, lysosomes and export. ribo- from ribose, a sugar · -some body Taught in Organelles and the cytoskeleton.
RNA (ry-boh-noo-KLAY-ik): Ribonucleic acid: a single-stranded nucleic acid with the sugar ribose and the base uracil in place of thymine. Messenger RNA carries a gene's message, ribosomal RNA forms much of the ribosome, and transfer RNA brings amino acids to it. ribo- ribose, the sugar Taught in From gene to protein.
sagittal plane (SAJ-ih-tul): A vertical plane that divides the body into right and left parts. The midsagittal plane runs down the midline and makes equal halves; a parasagittal plane runs off the midline and makes unequal parts. sagitta (Latin) arrow · para- beside Taught in Body planes and sections.
salt: An ionic compound that separates in water into cations and anions other than H+ and OH−, such as sodium chloride. An acid and a base react to form a salt and water. Taught in Acids, bases, pH and buffers.
saltatory conduction (SAL-tuh-tor-ee): The way an action potential travels along a myelinated axon: current flows under the myelin and the action potential is regenerated only at the nodes of Ranvier, so it seems to leap from node to node. It is fast and uses less energy. saltare to leap, to dance (Latin) Taught in The action potential in detail.
secondary active transport: Active transport in which a carrier uses one substance moving down its gradient, usually sodium, to move another against its gradient. In symport both move the same way; in antiport they move in opposite directions. The gradient it spends was built by the sodium–potassium pump. sym- together · anti- opposite · portare to carry · co- with Taught in Active transport and vesicles.
selective permeability: The property of a plasma membrane that lets some substances cross freely, lets others cross only through specific proteins, and keeps others out. The cell can change it by changing its membrane proteins. per- through · meare to pass Taught in The cell and its plasma membrane.
semilunar valves (sem-ee-LOO-nur): The pulmonary and aortic valves, at the exits from the right and left ventricles. Each has three pocket-shaped cusps that fill with blood slipping back toward the ventricle and seal the opening; they have no cords or muscles. semi- half · lun- moon Taught in Heart valves, septa and internal structure.
semipermeable membrane (sem-ee-PER-mee-uh-bul): A thin sheet that lets some substances cross and blocks others, also called a selectively permeable membrane. The membrane around each of your cells lets water, oxygen and carbon dioxide cross easily but holds back proteins and most ions. semi- partly · per- through · mea- pass Taught in Diffusion and osmosis.
sensation, integration and response: The three steps of every nervous system task: sensory input (sensory receptors detect a change), integration (neurons process the input and determine a response) and motor output (signals go to effectors). sens- feel, perceive · integr- whole · mot- move Taught in Organization of the nervous system.
sensory and motor divisions (AF-er-ent; EF-er-ent): The sensory (afferent) division carries signals from sensory receptors toward the CNS. The motor (efferent) division carries signals away from the CNS to effectors, the muscles and glands. af- toward · ef- away from · fer- carry · mot- move Taught in Organization of the nervous system.
sensory receptor (in a feedback loop): In a feedback loop, the cell or structure that detects a change in a regulated variable (also called the sensor). It is a whole cell or structure, not a receptor protein. sens- to perceive · recept- to receive Taught in Homeostasis and feedback loops.
septa of the heart (SEP-tuh): The dividing walls of the heart: the interatrial septum between the atria, the thick interventricular septum between the ventricles, and the atrioventricular septum between the atria and ventricles. saept- fence · inter- between Taught in Heart valves, septa and internal structure.
serous membrane (SEER-us): A thin, smooth sheet that lines the ventral body cavity and folds back over its organs: a parietal layer on the cavity wall, a visceral layer on the organ, and a film of watery serous fluid between them that lets the layers slide with little friction. The visceral layer on an organ is often called its serosa. ser/o watery fluid · paries (Latin) wall · viscera (Latin) internal organs Taught in Body cavities and serous membranes.
set point: The target value a feedback loop holds a regulated variable near, such as about 37 °C for body temperature. It sits inside the normal range and can shift, for example during a fever. Taught in Homeostasis and feedback loops.
shifts of the dissociation curve: Sideways moves of the dissociation curve. More carbon dioxide and H+ (the Bohr effect), higher temperature and more 2,3-BPG lower hemoglobin's affinity and shift it right, releasing more oxygen at a given PO2; the opposite changes, fetal hemoglobin and carbon monoxide shift it left. bis- twice · phosph- phosphate Taught in Oxygen transport.
signal amplification: The growth of a signal at each step of a pathway, so that a few messenger molecules produce a large response. One occupied receptor protein can switch on many G proteins, and each step after that multiplies again. amplificare to enlarge (Latin) Taught in Chemical messengers and receptors.
simple columnar epithelium: One layer of tall cells, often with microvilli or cilia and with goblet cells that release mucus. It lines the digestive tract from the stomach through the intestines, the gallbladder and the uterine tubes. goblet cup Taught in Epithelial tissue.
simple cuboidal epithelium: One layer of cube-shaped cells with round, central nuclei, specialized for secretion and absorption. It lines kidney tubules, thyroid follicles and small ducts. Taught in Epithelial tissue.
simple diffusion across the membrane: Movement of a substance straight through the phospholipid bilayer, down its concentration gradient, with no protein involved. It works for small nonpolar and lipid-soluble molecules such as oxygen, carbon dioxide and steroids, and its rate rises in step with the gradient. dif- apart · fundere to pour Taught in Passive transport across membranes.
simple squamous epithelium: One layer of flat cells, giving the shortest path for diffusion and filtration. It lines the air sacs of the lungs; it is called endothelium in the heart and blood vessels and mesothelium on serous membranes. endo- within · meso- middle Taught in Epithelial tissue.
sinoatrial node (sy-noh-AY-tree-ul): The sinoatrial node: a patch of autorhythmic cells in the upper back wall of the right atrium, near the superior vena cava. It reaches threshold first, so it is the heart's pacemaker; a rhythm it sets is called sinus rhythm. Bachmann's bundle and the internodal pathways carry its signal quickly across the atria. sino- sinus (a cavity) · atri- atrium Taught in The conduction system and pacemaker cells.
skeletal muscle tissue: Muscle tissue of long, cylindrical, striated fibers, each with many nuclei at its edge. It is attached to bones, moves the body and is voluntary. skelet- dried body Taught in Muscle tissue types.
smooth muscle tissue (VIS-er-al): Muscle tissue of small, spindle-shaped, nonstriated fibers with one central nucleus. It forms the walls of hollow organs and blood vessels and is involuntary; also called visceral muscle. viscer- internal organs Taught in Muscle tissue types.
sodium channel inactivation: The closing of a voltage-gated sodium channel by its inactivation gate about a millisecond after the activation gate opens. An inactivated channel cannot open again until the membrane repolarizes and resets it. in- not Taught in The action potential in detail.
sodium–potassium pump: An ATP-splitting membrane protein (the Na+/K+ ATPase) that moves three sodium ions out of the cell and two potassium ions in per cycle, both against their gradients. It builds the sodium gradient and keeps cell volume steady. -ase enzyme Taught in Active transport and vesicles.
solution (chemistry): A mixture in which one substance, the solute, is spread evenly particle by particle through another, the solvent. In your body the solvent is almost always water. solut- loosened · solv- to loosen Taught in Water, solutions and concentration.
solutions, colloids and suspensions (KOL-oydz): A mixture is substances combined physically, without bonds between them. In a solution the particles are tiny and never settle; colloids hold larger particles that still do not settle; in a suspension the particles are large enough to settle on standing. koll- glue · -oid like · suspend- to hang Taught in Water, solutions and concentration.
somatic nervous system (so-MAT-ik): The part of the motor division that controls skeletal muscle. One motor neuron runs from the CNS to the muscle, it always excites the muscle, and most of its output is under conscious control. somat- body Taught in Organization of the nervous system.
somatotopic maps (soh-muh-TOT-uh-pee; hoh-MUNK-yoo-lus): The point-to-point map of the body along the primary somatosensory and primary motor cortex, with the legs on the medial surface and the face lowest on the side. Parts with dense sensory receptors or fine control (hands, lips, tongue) get the most cortex, drawn as the homunculus. soma body · topos place · homunculus little man Taught in Cortical functions, memory, language and sleep.
spatial and temporal summation: The adding together of postsynaptic potentials at the trigger zone. In temporal summation one input fires repeatedly in quick succession; in spatial summation several inputs fire at about the same time. An action potential fires if the sum reaches threshold. tempus time (Latin) · spatium space (Latin) Taught in Synapses and neurotransmitters.
spinal cord external anatomy (KOH-nus med-yoo-LAIR-iss; KAW-duh ee-KWY-nuh): The spinal cord runs from the foramen magnum to the conus medullaris, its cone-shaped end at about L1–L2 in adults. It is wider at the cervical enlargement (supplying the upper limbs) and the lumbar enlargement (lower limbs); below the conus, lumbar and sacral roots hang down the canal as the cauda equina. conus cone · medulla marrow · cauda tail · equus horse Taught in The spinal cord.
spinal cord in cross section: Cut across, the spinal cord shows butterfly-shaped gray matter inside (dorsal or posterior horns for sensation, ventral or anterior horns with motor neurons, and lateral horns with sympathetic neurons from T1 to L2) around a central canal, and white matter outside in posterior, lateral and anterior columns. The anterior median fissure marks the front and the posterior median sulcus the back. dorsal back · ventral belly · funiculus little cord Taught in The spinal cord.
spinal nerve: One of the 31 pairs of nerves (8 cervical, 12 thoracic, 5 lumbar, 5 sacral, 1 coccygeal) formed where a dorsal root and a ventral root join in the intervertebral foramen. Every spinal nerve is a mixed nerve, carrying both sensory and motor axons. spin- spine Taught in Spinal nerves and plexuses.
spirometry (spy-ROM-eh-tree): Measuring the volumes of air breathed in and out, and how fast they move. Forced spirometry gives the forced vital capacity (FVC) and FEV1, the volume blown out in the first second; a low FEV1/FVC ratio shows obstructive disease, and small lungs with a normal ratio suggest restrictive disease. spir- breathe · -metry process of measuring · ob- against · restrict- hold back Taught in Lung volumes and ventilation rates.
standard feedback examples: The loops this course returns to again and again: body temperature, blood pressure, glucose in the blood and red blood cell production (negative feedback), and childbirth contractions and blood clotting (positive feedback). Taught in Homeostasis and feedback loops.
stem cell: An unspecialized cell that can divide to renew itself and can also give rise to specialized cells. Taught in Cell division and differentiation.
stem cell potency (toh-TIP-uh-tent; ploo-RIP-uh-tent): The range of cell types a stem cell's descendants can become: totipotent (every cell plus the supporting tissues of pregnancy), pluripotent (every body cell type), multipotent (several related types), oligopotent (a few) or unipotent (one). toti- whole · pluri- many · multi- many · oligo- few · uni- one · potent- powerful Taught in Cell division and differentiation.
steroid (STEER-oyd; ko-LESS-ter-ol): A lipid built on four fused carbon rings. Cholesterol, the main one, sits in the boundary around cells and is the raw material for your other steroids. ster/o solid · -oid like Taught in Carbohydrates, lipids, proteins and nucleic acids.
stratified cuboidal and stratified columnar epithelium: Rare stratified epithelia named for cube-shaped or tall surface cells. They line some large ducts, such as those carrying sweat, and parts of the male urethra. Taught in Epithelial tissue.
stratified squamous epithelium (KAIR-uh-tin): Many layers of cells with flat cells at the surface, built to resist wear. The keratinized form, with dead keratin-filled surface cells, is the epidermis; the nonkeratinized form lines most of the mouth, the esophagus and the vagina. kerat- horn Taught in Epithelial tissue.
striation (stry-AY-shun): The fine light and dark bands across skeletal and cardiac muscle fibers, produced by actin and myosin stacked in lined-up repeating units. Smooth muscle has no bands and is nonstriated. stria streak Taught in Muscle tissue types.
stroke volume: The volume of blood one ventricle ejects in one beat: SV = EDV − ESV, about 70 mL at rest. Taught in The cardiac cycle.
structure of a nerve (en-doh-NOOR-ee-um, pair-ih-NOOR-ee-um, ep-ih-NOOR-ee-um): A nerve is a bundle of axons in the peripheral nervous system wrapped in three connective tissue layers: endoneurium around each axon, perineurium around each bundle (fascicle), and epineurium around the whole nerve. endo- within · peri- around · epi- upon · neur/o nerve Taught in Spinal nerves and plexuses.
suffix: A word part added at the end of a root that usually tells what kind of term it is: a condition (-itis, inflamed), a procedure (-ectomy, cutting out), a field (-logy, study of) or a description (-al, pertaining to). Taught in Medical word parts.
superficial and deep: Superficial means toward the body surface; deep means away from the surface, farther inside. Skin is superficial to muscle. superficies (Latin) surface Taught in Anatomical position and directional terms.
superior and inferior (KAW-dul): Superior means toward the head or above; inferior means toward the feet or below. Cranial (toward the head end) and caudal (toward the tail end) mean the same in a standing human. crani/o skull · cauda (Latin) tail Taught in Anatomical position and directional terms.
supine and prone (SOO-pine, PROHN): Supine means lying face up, on the back; prone means lying face down. They describe how the body is lying and do not change the meaning of any directional term. supinus (Latin) lying on the back · pronus (Latin) leaning forward Taught in Anatomical position and directional terms.
surfactant (sur-FAK-tunt): A film of about 90% lipids, mostly phospholipids, and 10% proteins that type II alveolar cells secrete onto the water lining the alveoli. It lowers surface tension, so the alveoli stay open and inflate more easily. surf-act-ant short for surface-active agent Taught in Trachea, bronchial tree, alveoli and lungs.
synapse (basic) (SIN-aps): The junction where a neuron passes a signal to another cell. The presynaptic (sending) and postsynaptic (receiving) cells are separated by a gap about 20 nanometers wide, the synaptic cleft. syn- together · haptein to fasten (Greek) · pre- before · post- after Taught in Chemical messengers and receptors.
synapse (in detail) (SIN-aps): A junction where a neuron passes a signal to another cell. The presynaptic neuron sends the signal from its axon terminal; the postsynaptic neuron receives it, usually on a dendrite or the cell body. syn- together · haptein to fasten (Greek) · pre- before · post- after Taught in Synapses and neurotransmitters.
synovial membrane (sih-NOH-vee-al): A connective tissue membrane, with no epithelium, that lines the cavities of movable joints and releases a thick, slippery fluid that reduces friction. syn- together · ov/o egg Taught in Body membranes and tissue repair.
systemic circuit (sis-TEM-ik): The loop that carries oxygenated blood from the left ventricle through the aorta and its branches to the capillaries of every tissue except the lung's air sacs, and back through veins and the venae cavae to the right atrium. It works at high pressure. system- the whole body Taught in Blood flow through the heart and the two circuits.
systole and diastole (SIS-tuh-lee; dy-AS-tuh-lee): Systole is the contraction phase of a heart chamber and diastole is its relaxation and refilling phase. One cardiac cycle is one full heartbeat, from the start of one beat to the start of the next. systol- contraction · diastol- expansion Taught in Blood flow through the heart and the two circuits.
target cell: Any cell that carries receptor proteins for a particular messenger. Cells without those receptor proteins do not respond, however much messenger reaches them. Taught in Chemical messengers and receptors.
tendons and ligaments (ap-oh-noo-ROH-sis): Cords of dense regular connective tissue. A tendon joins muscle to bone, a ligament joins bone to bone, and an aponeurosis is a tendon spread into a flat sheet. apo- off, away from · neur- sinew Taught in Connective tissue.
the eleven organ systems: The eleven organ systems: integumentary, skeletal, muscular, nervous, endocrine, cardiovascular, lymphatic, respiratory, digestive, urinary and reproductive. integumentum (Latin) covering · endo- within · -crine to release · cardi/o heart · vascul/o small vessel Taught in Levels of organization and organ systems.
the four primary tissue types: The four kinds of tissue that build every organ: epithelial tissue (covers and lines), connective (supports and binds), muscle (contracts) and nervous tissue (carries electrical signals). Taught in Epithelial tissue.
the kidneys set blood volume: The principle that blood volume is set by how much sodium and water the kidneys excrete, the one loss route adjusted to match intake. Water follows sodium, so keeping sodium keeps fluid in the plasma and interstitial fluid. Taught in Long-term blood pressure regulation.
the long refractory period of cardiac muscle (ree-FRAK-tuh-ree): In cardiac muscle the absolute refractory period lasts about 200 to 250 ms, because the sodium channels stay inactivated through the plateau. It lasts nearly as long as the contraction, so a new action potential cannot start until the cell is relaxing, and twitches cannot sum into tetanus. refractarius stubborn (Latin) Taught in Cardiac muscle cells and their action potential.
the major organs of each system: The main organs of each organ system, such as the brain and spinal cord (nervous), the heart (cardiovascular), the lungs and trachea (respiratory), the stomach and liver (digestive), the kidneys, ureters, urinary bladder and urethra (urinary), and the gonads (reproductive). gon- seed, offspring · peri- around · cardi/o heart Taught in Levels of organization and organ systems.
the pump maintains the gradients: The sodium–potassium pump keeps the sodium and potassium gradients steady by replacing ions that leak. Its direct effect on the resting voltage is only a few millivolts; if it stops, the gradients and the resting potential fade slowly. Taught in The resting membrane potential.
the secretory pathway (sih-KREE-tuh-ree): The route taken by proteins bound for secretion, the plasma membrane or lysosomes: made on ribosomes docked on the rough ER, modified in the ER and Golgi apparatus, then carried in vesicles to their destination, ending in exocytosis for secreted proteins. secret- separated, set apart Taught in From gene to protein.
the three main parts of a cell (SY-toh-plaz-um): The three main parts of a typical cell: the plasma membrane (the outer boundary), the cytoplasm (everything inside the membrane except the nucleus) and the nucleus (the compartment that stores the cell's genetic instructions). cyto- cell · -plasm formed material Taught in The cell and its plasma membrane.
thoracic cavity (thuh-RAS-ik): The part of the ventral body cavity above the diaphragm, enclosed by the chest wall. It holds the two pleural cavities and, between them, the mediastinum. thorax (Greek) chest Taught in Body cavities and serous membranes.
threshold: The membrane potential, about −55 mV in a typical neuron, at which enough voltage-gated sodium channels open that sodium entry outpaces potassium exit and an action potential starts. Taught in Electrical signals: graded potentials and action potentials.
tight junction: A continuous band where strands of claudin and occludin proteins stitch the membranes of neighboring cells together. It seals the space between cells, so substances must pass through the cells rather than between them. Taught in Cell junctions.
tissue: A group of similar cells, plus the material around them, that work together to do one job. The study of tissues is histology. hist/o tissue · -logy study of Taught in Levels of organization and organ systems.
tissue membranes: A thin sheet of tissue that covers a body surface or lines a body cavity or hollow organ. An epithelial membrane is an epithelium on connective tissue (mucous, serous, cutaneous); a connective tissue membrane has no epithelium (synovial). Taught in Body membranes and tissue repair.
tissue repair (pah-RENG-kih-mah): The replacement of damaged tissue, either by regeneration (the same kind of working cells divide and replace the lost ones) or by fibrosis (fibroblasts fill the gap with collagen, forming scar tissue). The parenchyma is an organ's working cells. re- again · gener/o to produce · fibr/o fiber · -osis condition Taught in Body membranes and tissue repair.
tonicity (toh-NIS-ih-tee; kreh-NAY-shun): How a solution changes a cell's volume, set by the solutes that cannot cross the membrane. In an isotonic solution the cell keeps its volume, in a hypotonic one it swells and may burst (osmotic hemolysis), and in a hypertonic one it shrinks (crenation, in red blood cells). ton- tension · iso- equal · hypo- under · hyper- over · crena notch · hemo- blood · -lysis breaking apart Taught in Passive transport across membranes.
trachea (structure) (TRAY-kee-uh; kuh-RYE-nuh; tray-kee-AL-iss): The windpipe, from the larynx to its division in the chest. It is held open by 16 to 20 C-shaped rings of hyaline cartilage (tracheal cartilages), open at the back, where the smooth trachealis muscle closes the gap against the esophagus. The last cartilage forms the carina, a sensitive ridge where the trachea splits into the primary bronchi. trache- rough (windpipe) · carina keel Taught in Trachea, bronchial tree, alveoli and lungs.
transcription (tranz-KRIP-shun): Copying a gene's DNA sequence into RNA in the nucleus. RNA polymerase binds at the gene's promoter and builds a complementary RNA; splicing then removes the introns and joins the exons. trans- across · script- to write · exon from expressed region · intron from intragenic (within-gene) region Taught in From gene to protein.
transitional epithelium: A stratified epithelium whose dome-shaped surface cells flatten when the organ stretches, so the sheet thins without tearing. It lines the ureters, urinary bladder and first part of the urethra; also called urothelium. uro- urine Taught in Epithelial tissue.
translation (tranz-LAY-shun): Building a polypeptide on a ribosome by reading the codons of an mRNA in order, with tRNAs bringing the matching amino acids. Several ribosomes reading one mRNA at once form a polyribosome. trans- across · lat- carried · poly- many Taught in From gene to protein.
transverse plane: A horizontal plane that divides the body into superior (upper) and inferior (lower) parts. The cut surface it makes is a cross section. trans- across Taught in Body planes and sections.
tributaries of the venae cavae (VEE-nee KAY-vee; JUG-yoo-lur; AZ-ih-gus): The veins that drain into the superior and inferior venae cavae. Above the diaphragm, internal jugular and subclavian veins form the two brachiocephalic veins, which form the superior vena cava; the azygos vein joins it from the chest wall. Below, the common iliac veins form the inferior vena cava, which receives lumbar, gonadal, renal and hepatic veins. tribut- paid in · jugul- throat · a- without · zyg- yoke, pair · hemi- half Taught in The major systemic veins.
triglyceride (try-GLISS-er-ide): A lipid made of one glycerol joined to three fatty acids, the long carbon and hydrogen chains with a carboxyl group at one end; it is the main form of stored fat. Saturated fatty acids have only single bonds and run straight; unsaturated ones have at least one double bond, which bends the chain. tri- three Taught in Carbohydrates, lipids, proteins and nucleic acids.
up-regulation and down-regulation: Changes in how many receptor proteins a target cell carries. Long exposure to high messenger levels causes down-regulation (fewer receptor proteins, weaker response); long exposure to low levels causes up-regulation (more receptor proteins, stronger response). Taught in Chemical messengers and receptors.
varicose veins (VAIR-ih-kohs): Swollen, lengthened, twisted superficial veins, usually in the legs, caused when venous valves become incompetent: blood falls back, pools and stretches the thin wall, which pulls the next valve open in turn. varix dilated vein Taught in Structure of blood vessels.
vasoconstriction and vasodilation (vay-zoh-kun-STRIK-shun): Vasoconstriction is narrowing of a blood vessel when the smooth muscle in its wall contracts; vasodilation is widening when that muscle relaxes. Because resistance depends on the fourth power of the radius, both change flow sharply. vaso- vessel · constrict- squeeze · dilat- widen Taught in Muscle tissue types.
veins as a blood reservoir: The blood held in the systemic veins and venules, about 60 to 65 percent of the total at rest. Veins are highly compliant, so they store blood with little rise in pressure, and sympathetic venoconstriction can shift that stored blood toward the heart. Taught in Structure of blood vessels.
veins of the limbs (seh-FAL-ik; buh-SIL-ik; KYOO-bih-tul; suh-FEE-nus): Deep limb veins run beside the arteries and share their names (radial, ulnar, brachial, axillary; tibial, fibular, popliteal, femoral). Superficial veins run under the skin: the cephalic, basilic, median cubital and median antebrachial veins of the arm, and the great and small saphenous veins, which start from the dorsal venous arch of the foot. cephal- head · cubit- elbow · ante- before · brachi- arm · saphen- clearly visible Taught in The major systemic veins.
venous drainage of the brain (SAJ-ih-tul; SIG-moyd; KAV-er-nus): The brain's veins drain into dural venous sinuses, channels between the layers of the dura mater with no smooth muscle and no valves. The superior sagittal and straight sinuses drain to the transverse sinuses, then the sigmoid sinuses, which leave the skull as the internal jugular veins. The cavernous sinuses lie beside the sphenoid bone. sagitt- arrow · trans- across · sigm- the letter S · cavern- cave Taught in The major systemic veins.
venous return: The flow of blood back to the heart through the veins, driven by a small pressure gradient and helped by the skeletal muscle pump, the respiratory pump and venoconstriction, with venous valves preventing backflow. Taught in Structure of blood vessels.
ventilation–perfusion coupling: The matching of blood flow (perfusion) to airflow (ventilation) in each region of the lungs. The ventilation–perfusion ratio, V/Q, is about 0.8 for the whole lung; low alveolar PO2 constricts nearby pulmonary arterioles (hypoxic pulmonary vasoconstriction), sending blood to better-ventilated alveoli. per- through · fus- pour · hypo- under · ox- oxygen Taught in Gas exchange.
ventral body cavity: The large anterior main body cavity of the trunk. The diaphragm divides it into the thoracic cavity above and the abdominopelvic cavity below. venter (Latin) belly Taught in Body cavities and serous membranes.
ventricles of the brain (VEN-trih-kulz; AK-wuh-dukt): The four connected fluid-filled chambers inside the brain, left from the hollow of the neural tube: two lateral ventricles, the third ventricle and the fourth ventricle. The interventricular foramina and the cerebral aqueduct join them, and the median and lateral apertures open the fourth ventricle into the subarachnoid space. ventriculus little belly · foramen opening · aqua water · ductus channel · apertura opening Taught in Meninges, ventricles and cerebrospinal fluid.
ventricular muscle action potential: The action potential of a contractile ventricular cell, lasting about 250 to 300 ms: a fast sodium upstroke (phase 0), a small notch (phase 1), a plateau near 0 mV where calcium entry balances potassium exit (phase 2), repolarization by potassium exit (phase 3), and rest at about −90 mV (phase 4). cardi/o heart · -ac pertaining to Taught in Cardiac muscle cells and their action potential.
venules and veins (VEN-yool): Venules drain capillaries and merge into veins, which carry blood toward the heart at low pressure. Veins have a thin tunica media, a thick tunica externa, a wide lumen and, in the limbs especially, venous valves; they are capacitance vessels that hold large volumes of blood. ven- vein · -ule small Taught in Structure of blood vessels.
vesicle (VES-ih-kul): A small sphere of membrane that carries cargo within a cell. It buds off one membrane and fuses with another. vesica bladder · -cle small Taught in Organelles and the cytoskeleton.
voltage (VOLE-tij): The difference in electrical potential energy per unit of charge between two points, also called potential difference, measured in volts. It exists only where charge is separated; voltages across the membranes around cells are a few tens of millivolts (mV; 1 mV = 0.001 V), written as the inside compared with the outside. milli- one thousandth Taught in Charge, voltage and current.
voltage-gated sodium and potassium channels: Channels that open when the membrane depolarizes. Sodium channels open fast, then close on their own; potassium channels open slowly and close slowly. Together they shape the action potential. Taught in Electrical signals: graded potentials and action potentials.
voltage-gated, ligand-gated and mechanically gated channels: The three main kinds of gated ion channel, named for what opens them: voltage-gated channels open when the voltage across the membrane changes, ligand-gated channels open when a specific molecule binds, and mechanically gated channels open when the membrane is stretched or pressed. ligare to bind Taught in Passive transport across membranes.
water-soluble and lipid-soluble messengers: Water-soluble (hydrophilic) messengers cannot cross the plasma membrane, so they bind receptor proteins on the cell surface and act fast. Lipid-soluble (hydrophobic) messengers, such as steroids, diffuse through the membrane, bind receptor proteins inside the cell and act slowly by changing gene expression. Taught in Chemical messengers and receptors.
what sets vascular resistance: Vascular resistance is set by vessel length, blood viscosity and, most strongly, vessel radius, because resistance depends on 1 ÷ radius⁴. Total peripheral resistance (TPR) is the resistance of the whole systemic circulation; most of it is in the arterioles. periph- around, the outer edge Taught in Blood pressure, flow and resistance.
what the hypothalamus controls: The hypothalamus regulates body temperature, water balance and thirst, hunger, autonomic output (heart rate, blood pressure, digestion), the daily sleep-wake timing and the body's side of emotion, and it controls the pituitary gland. It acts through autonomic neurons, hormones and drives. Taught in Regions of the brain.
where cartilage is found (meh-NIS-kus; meh-NIS-kye): Hyaline cartilage forms articular cartilage on bone ends, the nose tip and the trachea's rings; fibrocartilage forms intervertebral discs and the menisci of the knee; elastic cartilage forms the ear flap and epiglottis. articul- joint · inter- between · menisc- crescent Taught in Connective tissue.
where each tissue is found (al-VEE-oh-lye): Where each epithelium is found: the epidermis (outer skin) over the dermis, thyroid follicles, alveoli (lung air sacs), the epiglottis and others. Each site's lining matches the wear and exchange it faces. derm- skin · alveol- small hollow · glott- tongue Taught in Epithelial tissue.
why the left ventricle wall is thicker: The left ventricle wall is about three times thicker than the right because it pumps into the high-resistance vessels of the whole body and must generate about five times the pressure; heart muscle thickens when it works against a heavier load. On average, both ventricles pump the same volume per beat. Taught in Heart valves, septa and internal structure.
why valves open and close: Heart valves are passive: a valve opens when pressure behind it (upstream) is higher than pressure in front of it, and closes when pressure in front becomes higher and blood starts to flow backward. Taught in The cardiac cycle.
word root: The part of a medical term that carries its core meaning, usually a body part or substance, such as cardi (heart) in cardiology. A root plus a linking vowel, usually o, is a combining form, written cardi/o. Taught in Medical word parts.

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