Questions: Test 3 Ch 19 The opening and closing of the heart valves is caused by Multiple Choice contraction and relaxation of papillary muscles that pull on heart strings. contraction of the smooth muscle in the walls of the great vessels leaving the heart. action potentials within the cusps of the valves. pressure changes of alternating contraction and relaxation during the cardiac cycle.

Test 3 Ch 19
The opening and closing of the heart valves is caused by
Multiple Choice
contraction and relaxation of papillary muscles that pull on heart strings.
contraction of the smooth muscle in the walls of the great vessels leaving the heart.
action potentials within the cusps of the valves.
pressure changes of alternating contraction and relaxation during the cardiac cycle.

Transcript text: Test 3 Ch 19 The opening and closing of the heart valves is caused by Multiple Choice contraction and relaxation of papillary muscles that pull on heart strings. contraction of the smooth muscle in the walls of the great vessels leaving the heart. action potentials within the cusps of the valves. pressure changes of alternating contraction and relaxation during the cardiac cycle.

Solution

The answer is the fourth one: pressure changes of alternating contraction and relaxation during the cardiac cycle.

Explanation for each option:

Contraction and relaxation of papillary muscles that pull on heart strings.
This is incorrect. While papillary muscles and chordae tendineae (heart strings) help prevent valve prolapse, they do not cause the opening and closing of the heart valves. The primary function of these structures is to stabilize the valves during ventricular contraction.
Contraction of the smooth muscle in the walls of the great vessels leaving the heart.
This is incorrect. The smooth muscle in the walls of the great vessels (such as the aorta and pulmonary artery) does not control the opening and closing of the heart valves. These muscles help regulate blood pressure and flow but are not directly involved in valve operation.
Action potentials within the cusps of the valves.
This is incorrect. Action potentials are electrical signals that trigger muscle contractions, but they do not occur within the valve cusps themselves. The opening and closing of the valves are mechanical processes driven by pressure changes, not electrical activity within the valve tissue.
Pressure changes of alternating contraction and relaxation during the cardiac cycle.
This is correct. The heart valves open and close in response to pressure changes in the heart chambers during the cardiac cycle. When the pressure in one chamber exceeds that in the adjacent chamber, the valve opens to allow blood flow. Conversely, when the pressure is higher in the receiving chamber, the valve closes to prevent backflow.

In summary, the opening and closing of the heart valves are primarily driven by pressure changes during the cardiac cycle.

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