Free Human Heart MCQs with Answers

31. The thymus gland is essential for immunity because it is the site where

• A. T lymphocytes mature
• B. red blood cells are produced
• C. antibodies are stored
• D. platelets are formed

Explanation: Immature lymphocytes from the bone marrow migrate to the thymus, where they learn to distinguish self from non self. This education is why a defective thymus causes severe immune deficiency in childhood.

32. Lymph differs from blood in that lymph

• A. contains more red blood cells than blood
• B. has no red blood cells and less protein
• C. flows away from the heart through arteries
• D. contains no white blood cells

Explanation: Lymph is essentially filtered tissue fluid, so it lacks erythrocytes and is poorer in plasma proteins, though it carries lymphocytes. It moves towards the heart in one direction, unlike blood in arteries.

33. Lymph nodes often swell during an infection because

• A. they fill with excess tissue fluid
• B. bacteria dissolve inside them
• C. lymphocytes multiply rapidly inside them to fight the pathogen
• D. their valves close and trap lymph

Explanation: Trapped antigens trigger lymphocyte proliferation within the node, enlarging it and making it tender. Swollen glands in the neck during a sore throat are immune factories at work, not fluid accumulation.

34. Like veins, the larger lymphatic vessels contain

• A. thick muscular walls like arteries
• B. red blood cells
• C. pacemakers
• D. valves that keep the lymph moving in one direction

Explanation: Lymph flows under very low pressure, so valves prevent backflow while surrounding muscle contractions squeeze it onwards. This one way design is why lymphoedema develops when the vessels are blocked.

35. Blood clotting requires

• A. Vitamin A
• B. Vitamin K
• C. Vitamin C
• D. Vitamin D

Explanation: Vitamin K is required for synthesis of clotting factors II, VII, IX, and X in the liver.

36. Fibrinogen is converted to fibrin by

• A. Prothrombin
• B. Thrombin
• C. Calcium
• D. Platelets

Explanation: Thrombin converts soluble fibrinogen to insoluble fibrin, forming the mesh of blood clots.