Question

Which one of the following statements is correct?

• A. The atrioventricular node (AVN) generates an action potential to stimulate atrial contraction
• B. The tricuspid and the bicuspid valves open due to the pressure exerted by the simultaneous contraction of the atria
• C. Blood moves freely from atrium to the ventricle during joint diastole
• D. Increased ventricular pressure causes closing of the semilunar valves

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
The cardiac cycle involves a sequence of pressure changes and valve actions that ensure one-way blood flow through the heart.
Detailed Explanation:
- (1) Incorrect: The Sino-atrial node (SAN) is the pacemaker that initiates the action potential for atrial contraction. The AVN delays and then conducts it to the ventricles.
- (2) Incorrect: During atrial systole, the valves are already open; the contraction simply pushes the remaining 30% of blood into the ventricles.
- (3) Correct: During joint diastole, all four chambers are in a relaxed state. The tricuspid and bicuspid valves are open, allowing blood from the pulmonary veins and vena cava to flow freely into the left and right ventricles respectively.
- (4) Incorrect: Increased ventricular pressure during systole opens the semilunar valves to pump blood into the aorta and pulmonary artery. They close when ventricular pressure drops during diastole.
Step 2: Final Answer:
Statement (3) correctly describes the blood flow during joint diastole.