Question

52 when atria Contracts ventricles​

Answer 1

Explanation:

Ali Ostadfar PhD, in Biofluid Mechanics, 2016

4.1.2 The Cardiac Cycle

The cardiac cycle describes the sequence of electrical and mechanical events that occurs with every heartbeat. The normal duration of a cardiac cycle for a heart rate of 75 beats/minutes is 0.8 seconds [3],

(4.1)

The cardiac cycle may be divided into phases in any number of methods, for instance four phases [1,3] or seven phases [2]. In the four phases method, the opening and closing of the heart valves explains this method of the cardiac cycle. These phases are [1,3]:

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Phase I: Filling period—the inlet valve is opened to fill the ventricle and the outlet valve is closed. The volume of blood in the ventricle increases from about 45 mL (from previous cycle) to about 115 mL.

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Phase II: Period of isovolumetric contraction—both valves are closed, blood volume is constant but the blood pressure increases to about 80 mmHg.

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Phase III: Period of ejection—the outlet valve of the ventricle is opened and the inlet is closed and due to more contraction, the blood pressure rises.

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Phase IV: Period of isovolumetric relaxation—both valves are closed and intraventricular pressure decreases without any blood volume changes.

Answer 2

Answer:

In late diastole, the contraction of the atria propels the remaining 25% of the blood into the ventricles, which produces a further increase in atrial and ventricle pressures (point B). Contraction of the ventricle then follows, signaling the onset of mechanical systole.

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