Cardiovascular System Questions and Answers

Answer: B

The vessel is the Pulmonary artery.

The pulmonary artery leaves the right ventricle and carries deoxygenated blood to the lungs, where it picks up oxygen. It is the one artery in adult circulation that carries deoxygenated blood.

The pulmonary veins carry oxygenated blood from the lungs back to the left atrium. The aorta carries oxygenated blood from the left ventricle to the body, and the coronary arteries supply oxygenated blood to the heart muscle.

Answer: D

The average pH of blood is 7.4.

Arterial blood is normally kept between 7.35 and 7.45, slightly alkaline, by buffers such as bicarbonate, together with the lungs and kidneys. Below 7.35 is acidosis and above 7.45 is alkalosis.

A pH of 7.0 is severe acidosis, and 6.0 and 6.4 are far outside the range compatible with life, so none of them is the normal value.

Answer: B

The correct matching is 1-d, 2-a, 3-b, 4-c.

• Pericardium: the double-layered sac forming the outer covering of the heart (d).
• Myocardium: the thick middle layer of cardiac muscle that does the pumping (a).
• Endocardium: the inner lining of the heart chambers and valves (b).
• Endothelium: the smooth single layer of cells lining the whole heart and the blood vessels (c).

Pericardium-outer and myocardium-middle are the two pairs that settle it; only one option has both.

Answer: B

The SA node acts as the pacemaker of the heart.

The sinoatrial node, a small mass of specialised muscle in the wall of the right atrium, fires electrical impulses on its own at about 60 to 100 per minute, faster than any other part of the conducting system. Each impulse spreads over the atria and then through the AV node to the ventricles, so the SA node sets the heart rate.

Blood pressure is regulated by the nervous and hormonal systems acting on the heart and vessels. Valves open and close passively with pressure changes, and blood is pumped by the contraction of the ventricular muscle, not by the node.

Answer: B

Fibrinogen is converted to fibrin by thrombin.

In the common pathway, thrombin (factor IIa) is a serine protease that cuts fibrinopeptides A and B from fibrinogen. The fibrin monomers then polymerise, and thrombin also activates factor XIII, which cross-links the fibrin into a stable clot.

Prothrombin is the inactive precursor that factor Xa turns into thrombin, so it cannot act on fibrinogen itself. Calcium is a cofactor in several steps, not the converting enzyme. Platelets form the primary plug and provide a surface for clotting, but they do not cleave fibrinogen.

Answer: B

The pacemaker potential is generated mainly by the funny current (If) through Na+ channels.

SA node cells have no stable resting potential. After each beat, as the membrane repolarises to about -60 mV, HCN channels open and carry an inward current, mostly of Na+. This is the 'funny' current, so named because it is activated by hyperpolarisation. It slowly depolarises the cell towards threshold, and T-type and then L-type Ca2+ channels complete the upstroke.

Fast sodium channels are largely inactivated at the SA node's resting voltage and produce the upstroke of ventricular cells, not pacemaker cells. Chloride channels and ATP depletion do not drive diastolic depolarisation.