NDA (II) 2018 General Ability Test · Question 84 of 146

Correct — A, the left auricle. Two rules settle it together. Blood always enters the heart through an atrium (auricle) and always leaves through a ventricle, so the receiving chamber must be one of the two atria. And the left side of the human heart handles oxygenated blood while the right side handles deoxygenated blood. Put the two together and the chamber that receives oxygenated blood returning from the lungs can only be the left auricle, which it reaches through the four pulmonary veins. From there it passes the bicuspid valve into the left ventricle, whose thick muscular wall pumps it into the aorta and out to the body.

• (b)left ventricle — The left ventricle handles the same oxygenated blood, but it does not receive it from the lungs — it receives it from the left auricle a moment later, and its job is to send it out to the whole body through the aorta. Ventricles are the pumping-out chambers, never the receiving chambers.
• (c)right auricle — This is the correct kind of chamber on the wrong side. The right auricle does receive blood, but deoxygenated blood coming back from the body through the superior and inferior venae cavae, not oxygenated blood from the lungs.
• (d)right ventricle — Wrong on both counts — wrong side and wrong kind of chamber. The right ventricle pumps deoxygenated blood out of the heart to the lungs through the pulmonary artery, which is the step immediately before the one this question asks about.

The human heart is a double pump running two circuits in series. In the pulmonary circuit, deoxygenated blood from the body enters the right auricle, drops into the right ventricle and is pumped through the pulmonary artery to the lungs. In the systemic circuit, oxygenated blood returns from the lungs through the pulmonary veins into the left auricle, drops into the left ventricle and is pumped through the aorta to the body. Keeping the two circuits separate — double circulation — is what lets birds and mammals sustain a high metabolic rate, because oxygenated and deoxygenated blood never mix.

Two exceptions catch students out, and both appear in this question's vocabulary. The pulmonary artery is the only artery in the body carrying deoxygenated blood, and the pulmonary veins are the only veins carrying oxygenated blood — because artery and vein are defined by direction of flow relative to the heart, not by oxygen content. The other useful anchor is wall thickness: the left ventricle has by far the thickest muscular wall because it has to drive blood around the entire body, while the right ventricle only has to reach the lungs. If an option ever asks which chamber has the thickest wall, that is the left ventricle, not the left auricle.

• Blood enters the heart through the auricles (atria) and leaves through the ventricles.
• The left auricle receives oxygenated blood from the lungs through the four pulmonary veins.
• The right auricle receives deoxygenated blood from the body through the superior and inferior venae cavae.
• The pulmonary artery is the only artery carrying deoxygenated blood, and the pulmonary veins the only veins carrying oxygenated blood.

• Assuming every artery carries oxygenated blood. The pulmonary artery does not.
• Mixing up receiving and pumping chambers — a ventricle never receives blood from outside the heart.
• Reading a heart diagram as though 'left' meant the left side of the page; in anatomy it means the patient's own left.

NDA asks which chamber receives or sends blood along a named vessel, or which vessel carries which kind of blood.

• practice — not a real PYQ

  Blood is carried from the heart to the lungs by the

  • (a)pulmonary vein
  • (b)pulmonary artery
  • (c)aorta
  • (d)vena cava

  Answer(b) pulmonary artery — the one artery in the body that carries deoxygenated blood, from the right ventricle to the lungs.

• practice — not a real PYQ

  Which chamber of the human heart has the thickest muscular wall?

  • (a)Right auricle
  • (b)Left auricle
  • (c)Right ventricle
  • (d)Left ventricle

  Answer(d) Left ventricle — it must generate enough pressure to drive blood through the entire systemic circuit.