59) DURING THE CARDIAC CYCLE

[Editor]

a) the second heart sound is caused by closure of the aortic and pulmonary valves
b) rapid ventricular filling occurs during diastole
c) the pressure in diastole is higher in the aorta than in the left ventricle
d) in mid diastole the pressure in the right atrium is higher than the right ventricle
e) the thin walled atria merely act as venous reservoirs

[Editor]

TTTTF

This is a difficult question that requires an understanding of the pressure changes within the various compartments during the 5 stages of the cardiac cycle. All of the above are true. You should be able to draw the cardiac cycle during the viva component of the exam and explain it!!

[shobi]

The Answer at the begining says that the last (e) stem is false. However, the explanation given says that all of the above is true hmy: - I think this may be misleading and would require further clarification.

[Editor]

shobi wrote:

The Answer at the begining says that the last (e) stem is false. However, the explanation given says that all of the above is true hmy: - I think this may be misleading and would require further clarification.

In comparison to the ventricals, the atria are thin walled. They need to generate enough pressure to force blood into the ventricles and open the relavent atrio-ventricular valves.The pressure required is however considerably less than that required for both the pulmonary and systemic circulations.

The answer to the last stem should correctly be false (F).The atrial muscle does contract and therefore the atria are not just venous reservoirs. The atrial kick contributes to the overall efficiency of ventricular contraction.Loss of this atrial kick in atrial fibrillation can lead to a reduction of the cardiac output in the region of 30%. This shows the importance of the atrial contraction within the cardiac cycle.