CDS (I) 2022 General Knowledge · Question 19 of 120

Correct — A, A-4, B-3, C-2, D-1. One rule settles three of the four rows. An artery is a vessel that carries blood AWAY from the heart and a vein is one that carries blood TO the heart, and that definition is about direction, not about whether the blood is oxygenated. So the pulmonary artery carries blood from the heart to the lungs, which is row 4, and the pulmonary vein brings it back from the lungs to the heart, which is row 1. The coronary artery is named for the crown of vessels around the heart itself, and its job is to supply the heart muscle with blood, which is row 2. That leaves capillaries with row 3, and it is the right one — capillaries are the microscopic vessels, one cell thick, that link the finest arteries to the finest veins and where the actual exchange of gases and nutrients happens.

• (b)A-4 B-2 C-3 D-1 — Gets the two pulmonary vessels right but swaps capillaries with the coronary artery, so it has capillaries feeding the heart muscle and the coronary artery acting as the link between arteries and veins.
• (c)A-1 B-2 C-3 D-4 — Reverses the pulmonary pair and shifts the other two as well — it has the pulmonary artery bringing blood from the lungs, which would make an artery carry blood towards the heart.
• (d)A-1 B-3 C-2 D-4 — The most tempting wrong option, because two of its four rows are right. It fails only on the pulmonary pair, sending the artery inwards and the vein outwards, which is the standard trap in every version of this question.

The human circulation is double: blood passes through the heart twice on each complete circuit. The right side of the heart pumps deoxygenated blood into the pulmonary artery to the lungs; the pulmonary vein brings the oxygenated blood back to the left side; the left side pumps it out through the aorta to the body; and the veins return it to the right side. The heart, being a muscle working continuously, needs its own supply, which the coronary arteries provide from the base of the aorta. Between the arterial and the venous side lie the capillaries — walls one cell thick, so that oxygen, carbon dioxide, nutrients and wastes can cross.

Match-list questions on the circulation almost always hide their difficulty in the same place, and it is the pulmonary pair. Because oxygenated blood is drawn red and deoxygenated blood blue in every textbook diagram, candidates start to think of arteries as the red vessels; the pulmonary artery then looks misnamed. Fixing the definition on direction rather than on colour removes the problem in one step. The two exceptions are worth stating out loud: the pulmonary artery is the only artery carrying deoxygenated blood, and the pulmonary vein the only vein carrying oxygenated blood. A blockage in a coronary artery starves the heart muscle of blood, and that is what a heart attack is.

• Arteries carry blood away from the heart and veins carry it towards the heart; the definition is about direction, not oxygen content.
• The pulmonary artery carries deoxygenated blood from the heart to the lungs — the one artery that does so.
• The pulmonary vein carries oxygenated blood from the lungs back to the heart — the one vein that does so.
• Coronary arteries branch from the base of the aorta to supply the heart muscle itself; a blockage there causes a heart attack.
• Capillaries are one cell thick and link the finest arteries to the finest veins, which is where exchange with the tissues takes place.

• Defining an artery by the colour in a diagram rather than by direction of flow.
• Reversing the pulmonary artery and the pulmonary vein, which is the standard trap in this item.
• Assuming exchange with tissues happens in arteries; it happens in the capillaries.

Almost always as a match list of vessels against functions, or as a single question on which artery carries deoxygenated blood.

• practice — not a real PYQ

  Which one of the following vessels carries oxygenated blood towards the heart?

  • (a)Aorta
  • (b)Pulmonary artery
  • (c)Pulmonary vein
  • (d)Vena cava

  Answer(c) Pulmonary vein — it returns oxygenated blood from the lungs to the left atrium, and it is the only vein carrying oxygenated blood.

• practice — not a real PYQ

  The exchange of oxygen, carbon dioxide and nutrients between the blood and the body tissues takes place in the

  • (a)arteries
  • (b)arterioles
  • (c)capillaries
  • (d)veins

  Answer(c) capillaries — their walls are a single cell thick, which is thin enough for substances to cross by diffusion.