Nose, pharynx and larynx

Pseudostratified ciliated columnar epithelium, with its goblet cells, is called respiratory epithelium because it lines most of the air passages. Simple squamous epithelium lines the alveoli, and keratinized stratified squamous epithelium is the epidermis.

• Simple squamous epithelium:
• Correct: Pseudostratified ciliated columnar epithelium:
• Keratinized stratified squamous epithelium:

The frontal, maxillary, sphenoid and ethmoid sinuses are air-filled spaces inside those skull bones, lined with mucous membrane and opening into the nasal cavity.

• Correct: They are air spaces in skull bones around the nasal cavity:
• They are blood-filled spaces in the brain's coverings:
• They are cartilage plates that shape the nose:

Cilia are short hair-like projections built on microtubules. They beat in coordinated waves and move a layer of fluid or mucus across the surface of the cell.

• Absorb nutrients from the surface:
• Anchor the cell to the basement membrane:
• Correct: Beat to move fluid or mucus across the cell surface:

Gases cross between air and blood only in the respiratory zone: the alveoli and the tiny airways whose walls carry alveoli. Everything above is conducting zone.

• In the lining of the nasal cavity and its conchae: The nasal cavity and its conchae are conducting zone. Their thick, glandular, ciliated lining warms, moistens and filters air but does not exchange gases with blood.
• In the larynx, between the vocal folds: The larynx is conducting zone. It guards the airway and makes sound; its walls are far too thick for gases to cross.
• Correct: In the alveoli and the tiny airways that carry them: Correct. Only the respiratory zone, where alveolar walls are a single thin layer of cells, exchanges gases with the blood.
• In the trachea and the air tubes below it: The trachea and the larger air tubes are conducting zone. They deliver air to the lungs; their walls of mucosa and cartilage are too thick for gas exchange.

The leaf-shaped flap of elastic cartilage standing up behind the base of the tongue is the epiglottis. It tips back over the opening of the larynx when you swallow.

• Thyroid cartilage: The thyroid cartilage is the large shield in the front wall of the larynx, lower down.
• Correct: Epiglottis: Correct. This flap at the top of the larynx is the epiglottis.
• Vestibular fold: The vestibular folds are folds of mucous membrane inside the larynx, just above the vocal folds.
• Hyoid bone: The hyoid bone is the U-shaped bone in front, below the jaw; the larynx hangs from it.

Mouth breathing bypasses the nasal cavity, where the conchae make air swirl against warm, blood-rich, mucus-covered surfaces. Air therefore arrives colder, drier and carrying more particles.

• It is warmer from the faster airflow: Faster air has less contact time with warm surfaces, so it is less warmed, not more.
• Correct: It is colder, drier and less filtered: Correct. Skipping the nasal cavity skips most of the warming, humidifying and filtering.
• It arrives just as warm, moist and clean: The pharynx adds some warmth and moisture, but the nasal cavity, with its conchae and dense blood supply, does most of the work, so skipping it changes the air.
• It carries more oxygen into her blood through the trachea: The trachea is conducting zone. No oxygen crosses into the blood there, however the air arrives.

The recurrent laryngeal nerves, branches of the vagus nerve, supply most of the small muscles that move the arytenoid cartilages and vocal folds. They run up beside the thyroid gland, so thyroid surgery can injure one and leave that vocal fold unable to close.

• Correct: The left recurrent laryngeal nerve: Correct. Without its nerve supply, the fold cannot be brought to the midline, so air leaks past and the voice is breathy.
• The muscles that lift the hyoid bone: The muscles that lift the hyoid bone raise the larynx during swallowing; they do not open or close the vocal folds.
• The left vestibular fold's lining: The vestibular folds do not make sound, so damage to one would not stop a vocal fold moving.
• The cricoid cartilage ring: A cricoid injury is unlikely in thyroid surgery and would not explain a single paralyzed fold.

The vocal folds must first close, so that the contracting abdominal wall muscles build up pressure against a sealed airway. Only then do the folds open suddenly and release the blast.

• An irritant touches sensory receptors in the lining of the trachea: Correct step. Sensory receptors in the lining of the larynx, trachea and large air tubes detect the irritant.
• Sensory fibers of the vagus nerve signal the brainstem: Correct step. The vagus nerve carries the sensory signal to the brainstem.
• A quick, deep breath is drawn in: Correct step. A deep breath in loads the lungs with air for the blast.
• Correct: The vocal folds open wide while the abdominal muscles contract: This is the wrong step. The folds close while the muscles contract, so pressure can build; with open folds the air would leak out gently.
• Air bursts out at high speed, carrying the irritant: Correct step. The sudden opening releases a high-speed blast.

The conchae break the airstream into narrow, turbulent channels. Heavier particles cannot follow the air around the bends and land on the sticky mucus that covers the conchae.

• They secrete antibodies directly into the air: The mucosa's mucus does contain antibodies, but they act on particles trapped in the mucus, not in the air.
• Correct: They swirl the air so particles strike the mucus: Correct. Turbulence throws particles against the mucus-covered surfaces.
• They squeeze the air so it moves faster: The conchae increase surface area and turbulence; their benefit is contact with the lining, not speed.
• They carry cilia that sweep particles out through the nares: Cilia in the nasal cavity sweep mucus backward toward the pharynx, where it is swallowed, not forward out of the nose.

Pitch depends on how fast the folds vibrate. Muscles that stretch the folds tighter and thinner make them vibrate faster, raising the pitch, as with a tightened guitar string.

• They are pushed apart more widely: A wider swing of the folds makes the sound louder, not higher.
• They are held completely open: Open vocal folds do not vibrate at all, so no voice is produced.
• More air pressure is built up beneath them: More pressure beneath the folds makes the sound louder; the question holds loudness constant.
• Correct: They are stretched tighter and thinner: Correct. Tighter, thinner folds vibrate faster, producing a higher pitch.