Question

At what stage during the cardiac cycle does pressure increase in the ventricles enough to close the AV valves but not yet open the Semilunar valves? What are some examples of mechanical digestion?

Answer 1

During isovolumic contraction, an early phase of ventricular systole, pressure rises in the ventricles to close the AV valves without opening the semilunar valves.

Step-by-step explanation:

The stage during the cardiac cycle when pressure increases in the ventricles enough to close the atrioventricular (AV) valves but not yet open the semilunar valves is known as isovolumic contraction or isovolumetric contraction. This occurs during the early phase of ventricular systole. After the atria contract and pump blood into the ventricles, the ventricles begin to contract, and as a result, the pressure within them rises. Once this pressure surpasses that of the atria, the AV valves close, which is signified by the first heart sound, S₁ or 'lub'.

Mechanical digestion refers to the physical breakdown of food into smaller pieces which can be more easily processed by the digestive system. Examples of mechanical digestion include the chewing of food in the mouth and the churning of food in the stomach.