Questions: Blood Composition and Function

Question 1

A patient has very low albumin levels in their blood. Which consequence would you most directly expect?

• A. Reduced oxygen-carrying capacity because albumin transports O₂
• B. Fluid leaking from blood vessels into surrounding tissues (edema), because osmotic pressure holding fluid in the vessels is reduced
• C. Increased clotting time because albumin is a clotting factor
• D. Elevated blood glucose because albumin normally signals insulin release

Answer: (B)

Albumin is the primary plasma protein responsible for maintaining colloid osmotic (oncotic) pressure — the osmotic force that draws water back into capillaries from surrounding tissues. Without sufficient albumin, this force is reduced and fluid accumulates in tissues, causing edema. This is a clinically important consequence of liver disease (which synthesizes albumin) or severe malnutrition. Albumin does not carry O₂ (hemoglobin does), is not a clotting factor, and does not regulate insulin.

Question 2

Mature human red blood cells contain a nucleus, which is why they can continuously produce hemoglobin throughout their 120-day lifespan.

• T. True
• F. False

Answer: False

Mature human erythrocytes eject their nucleus during development in the bone marrow. The resulting anucleate cells cannot divide, repair themselves, or synthesize new proteins — they contain a fixed amount of hemoglobin from the time of maturation. This is actually a functional adaptation: removing the nucleus and other organelles maximizes the internal space available for hemoglobin and makes the cell highly deformable (able to squeeze through narrow capillaries). After ~120 days, worn-out erythrocytes are recycled by the spleen and liver.

Question 3

Why is it misleading to equate 'white blood cell count' directly with the total number of leukocytes in the body?

Model answer: A standard white blood cell count measures only the leukocytes circulating in the bloodstream, but the majority of leukocytes at any given time reside in tissues (lymph nodes, spleen, connective tissue, etc.), not in circulation. The blood count is a snapshot of a small, mobile fraction of the total leukocyte pool.

Leukocytes use the bloodstream primarily as a highway to reach tissues where they are needed. Tissue-resident macrophages (derived from monocytes), lymphocytes in lymphoid organs, and neutrophils that have migrated into sites of infection are all outside the bloodstream. This is why a 'normal' blood WBC count does not mean the immune system is inactive — most of its workforce is already deployed in tissues.