Describe the circulation of blood through the heart and explain how the cardiac cycle is controlled.

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Describe the circulation of blood through the heart and explain how the cardiac cycle is controlled.

The blood circulatory system is responsible for providing a continuous flow of blood throughout the body to provide oxygen and nutrients to the tissues and remove the waste products and carbon dioxide. The circulatory system also acts as a means of transport for hormones and antibodies, and serves to distribute heat. The heart is the pump which tirelessly carries out the task of moving the blood around the body, beating at about 60 times a minute for an entire lifetime. It takes approximately one minute for blood to circulate from the heart, around the body and back again.

The heart consists of four chambers, two atria (labelled auricles on diagram) and two ventricles, and is mainly composed of muscle. It is lined with a thin layer of cells called the Endocardium, and is enclosed within a double layered membrane sac called the Pericardium, which attaches it to the breastbone, diaphragm and thorax membranes. The deoxygenated blood is carried into the heart directly by the Vena Cava vein; the Superior Vena Cava drains blood from the head, neck and arms, and the Inferior Vena Cava drains the blood from the rest of the body, and firstly enters the Right Atrium. The right of the heart deals with blood from the body. Veins carry deoxygenated blood towards the heart, and arteries carry oxygenated blood away from the heart. The blood flows from here into the right ventricle, and is kept from flowing back into the right atrium by the Tricuspid valve, which consists of three triangular flaps of membrane curved in the direction of blood flow. The valves in the heart serve to keep the blood flowing in one direction only, as the pressure of the blood against the valve forces its flaps together.

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The heart muscle contracts to pump the blood from the Right Ventricle through the Pulmonary Semi Lunar valve and into the Pulmonary artery, which splits into two branches leading to each of the lungs. This is the only artery that carries deoxygenated blood, because it is needed to carry blood to the lungs where it loses it’s carbon dioxide and absorbs oxygen through a network of fine capillaries.

The blood returning from the lungs is oxygenated, and enters the heart again through the two Left Pulmonary veins, into the Left Atrium. The blood flows from here ...

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