The lymphatic system

Under the revised Starling principle, fluid filters out along almost the whole capillary and does not reverse at steady state. A separate drainage route returns it to the blood.

• Correct: It filters out along almost the whole length:
• It filters out at one end and is fully reabsorbed at the other:
• It neither leaves nor enters:

The agranulocytes are lymphocytes and monocytes. Neutrophils, eosinophils and basophils are granulocytes.

• Neutrophils and eosinophils:
• Correct: Lymphocytes and monocytes:
• Basophils and neutrophils:

On each side, the internal jugular vein and the subclavian vein join to form the brachiocephalic vein. The lymphatic ducts empty at those junctions.

• Correct: The internal jugular and subclavian veins:
• The external and internal jugular veins:
• The axillary and cephalic veins:

The efferent lymphatic vessel leaves the node at the hilum, the indented side, carrying lymph out. There are only one or two, compared with several afferent vessels.

• Afferent lymphatic vessel: Afferent lymphatic vessels enter all over the curved outer surface, not at the hilum.
• Correct: Efferent lymphatic vessel: Correct. A single vessel leaving at the hilum is the efferent lymphatic vessel.
• High endothelial venule: High endothelial venules are small blood vessels in the paracortex, inside the node, where lymphocytes leave the blood.
• Trabecula: A trabecula is a partition of connective tissue running inward from the capsule. It does not leave the node.

The right lymphatic duct drains only the right arm, the right side of the chest and the right side of the head and neck. It empties where the right internal jugular vein meets the right subclavian vein.

• The thoracic duct, at the left internal jugular and subclavian veins: The thoracic duct drains the rest of the body, including the left arm and both legs, but not the right arm.
• The cisterna chyli, at the inferior vena cava: The cisterna chyli is a sac in the upper abdomen that collects lymph from the legs, pelvis and gut. It empties into the thoracic duct, not directly into a vein.
• The thoracic duct, at the right internal jugular and right subclavian veins: The thoracic duct empties on the left side, and it does not drain the right arm.
• Correct: The right lymphatic duct, at the right internal jugular and subclavian veins: Correct. Lymph from the right arm travels through nodes in the right armpit, the right subclavian trunk and the right lymphatic duct.

Losing the spleen removes a blood filter and a platelet reserve. Platelets and aging red cells rise in the blood, and defense against bacteria in the blood weakens for life, while the lymph nodes, which filter lymph, are unaffected.

• Platelet count in the blood: up. The spleen normally holds about a third of the platelets in reserve. Without it, those platelets stay in the circulating blood, and fewer are removed.
• Number of old or misshapen red blood cells circulating: up. Red pulp macrophages normally catch stiff, aging red cells that cannot squeeze through the slits into the venous sinuses. Without that squeeze test, more of them stay in circulation.
• Risk of an overwhelming bloodstream infection with sugar-coated bacteria: up. Red pulp macrophages and white pulp lymphocytes are the main defense against bacteria in the blood, especially sugar-coated ones that are hard to engulf elsewhere. The liver takes over only part of the job.
• Filtering of lymph by lymph nodes: no change. The spleen filters blood, not lymph: it has no afferent lymphatic vessels. The lymph nodes keep filtering lymph as before.

The endothelial cells of lymphatic capillaries overlap loosely. Fluid pushing in opens gaps large enough for proteins, and the flaps close behind them. Lymph then carries the protein back to the blood.

• Correct: Gaps between overlapping flaps of lymphatic capillaries let it in: Correct. Loose, overlapping endothelial flaps let protein into lymphatic capillaries, where blood capillaries would hold it out.
• Pumps in the tissue cells move it into blood capillaries: Tissue cells do not pump albumin into capillaries. Proteins return to the blood through the lymphatic route.
• Macrophages digest all of it where it lies: Macrophages do engulf debris, but they do not clear the steady stream of plasma protein. Protein that stays in tissue draws in fluid and causes swelling.
• Collecting lymphatic vessels absorb it through the thick muscle of their walls: Fluid and protein enter the lymphatic system at the capillaries. Collecting vessels carry lymph onward; their valves stop backflow rather than taking up protein.

Primary lymphoid organs are where lymphocytes are made and mature: the red bone marrow and the thymus. The others are secondary lymphoid organs, where mature lymphocytes meet antigens.

• Correct: Thymus: Correct. One main line of lymphocytes matures in the thymus.
• Spleen: The spleen is a secondary lymphoid organ: its white pulp is where lymphocytes meet antigens in the blood.
• Correct: Red bone marrow: Correct. Every lymphocyte is made in the red marrow, and one main line matures there.
• Palatine tonsil: The palatine tonsils are MALT, a secondary lymphoid tissue where lymphocytes meet antigens entering through the mouth.
• Lymph node: Lymph nodes are secondary lymphoid organs, where lymphocytes meet antigens carried in lymph.

Her capillaries filter at a normal rate, but the lymphatic route out of the arm was removed. Fluid and protein stay in the tissue, and white blood cells drawn into the stagnant fluid release signals that drive fibrosis and fat buildup, which is why the swelling has become firm and barely pits. This is secondary lymphedema.

• The capillaries of her arm filter far more than normal: Nothing in her story raises capillary pressure or makes the capillaries leakier. Her filtration is normal; drainage has failed.
• Correct: Filtered fluid and protein cannot drain out of her arm: Correct. With the armpit nodes and their vessels gone, the arm cannot return what it filters.
• Plasma protein has fallen, so less fluid is pulled back: Her albumin is normal, and a low plasma protein would cause swelling in both legs and elsewhere, not in one arm.
• Veins in her arm are blocked, raising capillary pressure: A blocked vein raises capillary pressure and causes low-protein, pitting edema. Her surgery removed lymphatic drainage, and the firm, protein-rich swelling fits that.

The spleen filters blood: its red pulp macrophages remove bacteria as blood squeezes from the cords into the venous sinuses, and its white pulp lymphocytes meet antigens in the blood.

• A lymph node: Lymph nodes filter lymph, which carries what enters the tissues. Bacteria placed straight into the blood bypass them.
• The thymus: The thymus is where lymphocytes mature. It does not filter blood or lymph.
• The palatine tonsil: The palatine tonsils sample what enters through the mouth, not the blood.
• Correct: The spleen: Correct. The spleen is the lymphoid organ that filters blood.

With more vessels coming in than going out and a wide network of sinuses between, lymph moves slowly through the node. The extra time lets macrophages lining the sinuses engulf bacteria, debris and cancer cells.

• It speeds up and is pushed through faster: The layout slows lymph rather than speeding it. The node is a filter, and a filter works better when flow is slow.
• It picks up red blood cells from the node: Lymph nodes do not add red blood cells to lymph; red cells stay in the blood vessels of the node.
• Correct: It slows down and lingers near macrophages: Correct. Slow flow gives the macrophages time to clear the lymph.
• It gains protein and loses lymphocytes: The reverse is closer to the truth: capillaries in the node take back water, and lymph leaves richer in lymphocytes, not poorer.