Question

Animal Physiology Question

1. Beginning with all chambers of the heart in the "relaxed" phase, describe the cardiac cycle in mammals, with systole and diastole of the atria and ventricles. For each time point in the cycle you select, state the following:

• Whether the atria and ventricles are contracting or relaxing.

• Whether the AV valves and semilunar valves are closed or open

• Whether the pressure in the atria and ventricles is high or low

Answer 1

The cardiac cycle in mammals involves four major stages of activities--

1) Isovolumic relaxation - during which AV Valves are closed . Semilunar Valves are closed . This stage comprise the ventricular diastole.

2) inflow Stage - including atrial systole, during which blood returning to heart flows through atria into relaxed ventricles. AV Valve is open and semilunar Valve is closed . This stage is called as ventricular filling stage.

3) Isovolumic contraction -- both AV Valve and Semilunar valves are closed . AV Valve closes at the end of ventricular diastole, blood flow stops ventricle begins to contract.

4) ventricular Ejection stage -- AV Valve is closed and Semilunar valves are open . Ventricles contract and blood flows from the heart to lungs and rest of the body.