MICROANATOMY

Detailed explanation-1: -Diastole begins with the closing of the aortic valve (or pulmonic) and ends with the closing of the mitral valve (or tricuspid). This period encompasses the ventricular relaxation and filling. Diastole represents when the blood vessels return blood to the heart in preparation for the next ventricular contraction.

Detailed explanation-2: -The cardiac cycle begins with atrial systole, the sequential activation and contraction of the 2 thin-walled upper chambers. Atrial systole is followed by the delayed contraction of the more powerful lower chambers, termed ventricular systole.

Detailed explanation-3: -During the middle part of a diastole a small volume of blood flows into the ventricles. This is the blood flowing from veins and passing the atria to fill the ventricles. The pressure in both ventricles is close to zero (fig. 5.1).

Detailed explanation-4: -The atrial systole, ventricular systole, atrial diastole, and ventricular diastole are clearly mentioned in the cardiac cycle diagram given below.

Detailed explanation-5: -The atria and ventricles alternately contract in each cardiac cycle. The pressures in the chambers change greatly over the course of the cardiac cycle. The cardiac cycle is essentially split into two phases, systole (the contraction phase) and diastole (the relaxation phase).