Question

In the cardiac cycle diastole is
A) The number of heart beats per minute
B) Relaxation period after contraction of the heart
C) The forceful pumping action of the heart
D) The contraction period after relaxation of the heart

Answer 1

Hint:Cardiac cycle is one cycle from the ending of one heartbeat to the starting of another heart beat. It has two periods - diastole and systole.

Complete answer:
The cardiac muscles of the heart contract and relax in a rhythmic cycle. During the contraction phase, called systole, blood is propelled out of the ventricles and into either the pulmonary or systemic circulations. During the relaxation phase, called diastole, blood fills the emptied ventricles.

When contraction stops, the ventricular muscle relaxes rapidly. The ventricular pressure almost immediately falls below aortic pressure, closing the aortic valve. However, ventricular pressure remains greater than atrial pressure, and the AV valve remains closed. This period of early diastole is called isovolumetric ventricular relaxation. As ventricular pressure falls below atrial pressure, the AV valve opens and ventricular filling occurs, rapidly at first and then slowing. As discussed earlier, ventricles fill to approximately 70 percent of capacity during diastole.

Option A: The number of heart beats per minute is known as the pulse rate and not diastole. Therefore, this is the incorrect option. The average pulse rate of humans is around 72 beats per minute,

Option B: The relaxation period after contraction of the heart is known as diatole. During this period the heart expands and refills with the blood which returns from the circulatory system. Therefore, this is the correct option.

Option C: Using a total artificial heart pump one can pump the heart forcefully. Therefore, this is the incorrect option.

Option D: The contraction period after relaxation of the heart is known as systole. Therefore, this is the incorrect option.

Thus, the correct option is (B) Relaxation period after contraction of the heart.


Note: The average adult person at rest has 65 to 75 heartbeats (cardiac cycles) per minute. One complete cardiac cycle takes about 0.8 seconds. Atrial systole, where the atria contract and eject blood into ventricles, lasts about 0.1 seconds. Ventricular systole, where ventricles contract and eject blood into large arteries, lasts 0.3 seconds.