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NEET 2022, Biology Q79: Blood Circulation in Human

NEET2022Biology
Q.

Which one of the following statements is correct ?

  1. A

    The atrio-ventricular node (AVN) generates an action potential to stimulate atrial contraction

  2. B

    The tricuspid and the bicuspid valves open due to the pressure exerted by the simultaneous contraction of the atria

  3. C

    Blood moves freely from atrium to the ventricle during joint diastole

  4. D

    Increased ventricular pressure causes closing of the semilunar valves.

Solution

During joint diastole, both atria and ventricles are relaxed. The semilunar valves are closed, the atrio-ventricular valves (tricuspid and bicuspid) are open, and blood flowing into the atria from the venae cavae and pulmonary veins passes freely into the ventricles. Statement (3) is correct.

The SAN (not AVN) initiates the heartbeat. AV valves open passively when atrial pressure exceeds ventricular pressure, not from atrial contraction directly. Increased ventricular pressure opens (not closes) the semilunar valves.

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