The brief delay of the impulse at the atrioventricular node is important because it
Correct answer: D. gives the atria time to empty into the ventricles before the ventricles contract
- A. slows the overall heart rate
- B. prevents the impulse from reaching the ventricles at all
- C. allows the semilunar valves to open early
- D. gives the atria time to empty into the ventricles before the ventricles contract
Explanation
A delay of about a tenth of a second lets atrial systole finish and the ventricles fill completely, so the following ventricular contraction ejects a full stroke volume. Without it the two sets of chambers would contract almost together and pumping would be very inefficient. The node conducts the impulse onwards rather than blocking it, and the semilunar valves open only after ventricular pressure has risen.
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About Cardiac Cycle and Heartbeat
The cardiac cycle describes atrial systole, ventricular systole and diastole, including pressure changes, blood movement and the opening or closing of heart valves. It also covers the conduction pathway from the sinoatrial node through the atrioventricular node, bundle of His and Purkinje fibres, and relates these events to heartbeat sounds.
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