The beginning of ventricular systole is when blood flowing back toward the relaxed ventricles causes the semilunar valves to close. The beginning of ventricular systole is when blood flowing back toward the relaxed ventricles causes the semilunar valves to close. A) TrueB) False

false.

Explanation:

These are the valves between the aorta and the left ventricles and between the pulmonary artery and the right ventricle.

Ventricular systole begins when the atrioventricular valves closes up due to rise in the pressure in the ventricles and the opening of seminular valves for blood to leave the ventricles into pulmonary and systemic circulation.

This signifies the beginning of ventricular contraction, as the closure of the atrioventricular Valves between the atria and the ventricles prevent the mixing up of oxygenated blood and deoxygenated blood in the ventricles. It ensures complete emptying of the ventricles before returning blood from the atria enters again for another cycle.

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Collectively they (semilunar valves) prevent back flow of blood from the arteries (aorta and pulmonary arteries) back into the ventricles.

The correct answer is "False".

Explanation:

The ventricular systole occurs when pressure rises in the ventricles causing that blood pumps from the right ventricle and into the aorta from the left ventricle. The beginning of this step is given when blood flowing back towards the atria, closing the tricuspid and mitral valves. It is false that the blood flows back towards the relaxed ventricles as it is stated in the question.