Free Circulation MCQs with Answers

21. The chambers of the heart that receive blood returning from the veins are the

• A. atria
• B. ventricles
• C. valves
• D. septum

Explanation: The right atrium collects deoxygenated blood from the venae cavae and the left atrium receives oxygenated blood from the pulmonary veins. Ventricles are the pumping chambers below, so direction of flow identifies each chamber.

22. The wall that separates the right ventricle from the left ventricle is the

• A. pericardium
• B. interventricular septum
• C. mitral valve
• D. aorta

Explanation: The muscular septum keeps oxygenated and deoxygenated blood completely separate, which is essential for the high efficiency of the mammalian double circulation. A hole in it, a septal defect, lets the two streams mix.

23. The valves found at the bases of the aorta and the pulmonary trunk are called

• A. bicuspid valves
• B. tricuspid valves
• C. semilunar valves
• D. atrioventricular valves

Explanation: Their three crescent shaped pockets fill with blood and snap shut when the ventricles relax, preventing backflow from the great arteries. The atrioventricular valves sit between atria and ventricles, a different position with different names.

24. The membrane that encloses and protects the heart is the

• A. pleura
• B. peritoneum
• C. meninges
• D. pericardium

Explanation: The pericardium anchors the heart in the chest and secretes fluid that lubricates its beating. The pleura covers the lungs and the peritoneum the abdominal organs, so the membrane names follow the organs they wrap.

25. The right ventricle pumps blood into the

• A. pulmonary artery, which carries it to the lungs
• B. aorta, which carries it to the body
• C. coronary artery, which feeds the heart muscle
• D. vena cava, which returns it to the heart

Explanation: The right side handles deoxygenated blood and sends it to the lungs for oxygenation, while the left side sends oxygenated blood to the body through the aorta. Remember right to lungs, left to body.

26. The walls of the atria are thinner than those of the ventricles because the atria

• A. pump blood only into the adjacent ventricles
• B. never contract at all
• C. pump blood to the whole body
• D. contain no muscle tissue

Explanation: Atria need only enough force to top up the ventricles below, so their muscle is thin. The left ventricle, which drives blood around the entire body, has the thickest wall of all four chambers.

27. The muscular layer of the heart wall, responsible for its contraction, is the

• A. epicardium
• B. pericardium
• C. myocardium
• D. endocardium

Explanation: The myocardium is cardiac muscle supplied by the coronary arteries, and its death during a heart attack is what damages the pump. The endocardium lines the chambers and the epicardium is the outer surface.

28. At a heart rate of 75 beats per minute, one complete cardiac cycle lasts about

• A. 0.1 second
• B. 0.4 second
• C. 1.2 seconds
• D. 0.8 second

Explanation: Sixty seconds divided by 75 beats gives 0.8 second per cycle, of which atrial contraction takes about 0.1, ventricular contraction 0.3 and the shared relaxation the rest. This arithmetic is a standard MDCAT calculation.

29. During ventricular systole

• A. the ventricles contract and the semilunar valves open
• B. the ventricles relax and fill with blood
• C. the semilunar valves close
• D. the atrioventricular valves open wide

Explanation: Systole means contraction: rising pressure in the ventricles closes the inlet atrioventricular valves and forces open the semilunar valves, ejecting blood into the arteries. Relaxation, diastole, is the opposite phase.

30. The second heart sound, dup, is produced by the closure of the

• A. atrioventricular valves
• B. semilunar valves
• C. coronary valves
• D. pulmonary veins

Explanation: When the ventricles relax, blood trying to flow back snaps the aortic and pulmonary semilunar valves shut, producing the shorter, sharper second sound. The first sound, lubb, comes from the atrioventricular valves closing.