3. Explain the action of the heart in terms of collecting blood, pumping blood, and opening and closing of valves

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While the right atrium is responsible for collecting blood from the superior vena cava and from the inferior vena cava, the left atrium is responsible for collecting blood from the pulmonary veins. The collected blood then flows into the right and left ventricle and is pumped into the arteries. The atrioventricular and semilunar valves are responsible for controlling and directing the blood flow. When the atria contracts, the atrioventricular valves open and the blood flows through them into the ventricle. The semilunar valves are closed so the ventricle can be filled with blood. Then, the ventricles contract causing a rise in the pressure, that causes the atrioventricular valves to close, preventing back flow of blood into the atria. The semilunar valves then open and allows the blood flow into the arteries, and the atria starts to fill with blood again.When the ventricles stop contracting, it leads to a fall in the pressure and causes the semilunar valves to close, preventing back flow of blood, as well as it allows the atrioventricular valves to re-open, and the cycle repeats.