Free Circulation MCQs with Answers

31. In an electrocardiogram, the P wave represents

• A. repolarisation of the ventricles
• B. contraction of the ventricles
• C. depolarisation and contraction of the atria
• D. closure of the heart valves

Explanation: The P wave records the spread of excitation across the atria, which then contract. The QRS complex shows ventricular depolarisation and the T wave ventricular recovery, so each deflection maps to a specific electrical event.

32. After the atrioventricular node, the impulse travels to the apex of the heart along the

• A. sinoatrial node
• B. coronary vein
• C. pulmonary vein
• D. bundle of His and Purkinje fibres

Explanation: The bundle of His carries the impulse down the septum and the Purkinje fibres spread it through the ventricle walls from the apex upwards, squeezing blood out efficiently. This pathway is why the ventricles contract as a unit.

33. During ventricular systole the atrioventricular valves

• A. close, preventing blood from flowing back into the atria
• B. open fully to let blood into the ventricles
• C. dissolve under pressure
• D. contract actively like muscle

Explanation: Rising ventricular pressure lifts the flaps of the tricuspid and bicuspid valves shut, and chordae tendineae anchored to papillary muscles stop them turning inside out. Their closure is the first heart sound.

34. In a blood pressure reading of 120 over 80 mmHg, the figure 120 represents the

• A. pulse rate per minute
• B. systolic pressure while the ventricles contract
• C. diastolic pressure while the heart relaxes
• D. average pressure of the cycle

Explanation: The higher number is recorded at ventricular contraction when arterial pressure peaks, and the lower number is the resting pressure during diastole. Both matter clinically, since sustained high values damage vessels.

35. Arteries have thick walls rich in elastic fibres because they

• A. carry deoxygenated blood only
• B. must collapse when empty
• C. must withstand and smooth out the high pressure of blood from the heart
• D. need to store lymph between meals

Explanation: Each heartbeat stretches the elastic walls, which then recoil and keep blood moving between beats, converting a pulsatile flow into a steadier one. Veins work at low pressure and so have thinner walls.

36. Blood flows most slowly in the capillaries because their

• A. walls are unusually thick
• B. total cross sectional area is enormous
• C. internal pressure is the highest of any vessel
• D. diameter exceeds that of the aorta

Explanation: Although each capillary is microscopic, together they present a huge total area, so the same volume of blood spreads out and slows, allowing time for exchange. Slow flow follows from area, not from wall thickness.

37. The vessel that carries deoxygenated blood from the heart to the lungs is the

• A. pulmonary artery
• B. pulmonary vein
• C. aorta
• D. coronary artery

Explanation: The pulmonary artery is the exception to the rule that arteries carry oxygenated blood, since it carries blood to the lungs to be oxygenated. The pulmonary vein reverses the pattern, carrying oxygenated blood back as a vein.

38. The largest artery of the human body is the

• A. carotid artery
• B. aorta
• C. femoral artery
• D. renal artery

Explanation: The aorta, about 2.5 cm in diameter, receives the entire output of the left ventricle and branches to every organ. All other systemic arteries are branches of it.

39. The superior and inferior venae cavae empty deoxygenated blood into the

• A. left ventricle
• B. left atrium
• C. right atrium
• D. aorta

Explanation: The venae cavae collect blood from the upper and lower body and deliver it to the right atrium, from where it passes to the right ventricle and on to the lungs. The left atrium receives blood from the lungs instead.

40. Blood pressure is lowest in the

• A. aorta
• B. arteries
• C. arterioles
• D. venae cavae

Explanation: Pressure falls steadily through arteries, arterioles and capillaries as energy is lost to friction, reaching near zero in the great veins. This is why venous return depends on valves, muscle contraction and breathing rather than on pressure.