ANATOMY

Detailed explanation-1: -Rapid ejection (b-c): As the semilunar valves open at point (b), there is a rapid ejection of blood due to increased ventricular contractility. The arterial pressure increases until reaching it maximum at point (c). This phase usually lasts for 13% of the cardiac cycle.

Detailed explanation-2: -The semilunar valves are closed because the ventricular pressure is lower than that in the aorta and the pulmonary artery (fig. 1.1). The contraction is represented by a colour change of myocardium. The ventricles contract and all valves are closed, so no blood can be ejected.

Detailed explanation-3: -The semilunar valves open when the ventricular muscle contracts and generates blood pressure within the ventricle higher than within the arterial tree. When the heart muscle relaxes the diastole phase begins again.

Detailed explanation-4: -Ejection begins when the intraventricular pressures exceed the pressures within the aorta and pulmonary artery, which causes the aortic and pulmonic valves to open.

Detailed explanation-5: -In the second phase of ventricular systole, the ventricular ejection phase, the contraction of the ventricular muscle has raised the pressure within the ventricle to the point that it is greater than the pressures in the pulmonary trunk and the aorta.