What is the Human Circulatory System? The main organ of the circulatory system is the Human Heart. The other main parts of the circulatory system include the Arteries, Arterioles, Capillaries, Venules, Veins and Blood. The lungs also play a major part in the pulmonary circulation system.

Functions of the circulatory system

The function of a humans circulatory system is to transport blood around the body. The blood itself also carries numerous other substances which the body requires to function.

The main substance being Oxygen, carried by a protein called haemoglobin, found inside red blood cells. White blood cells are also vital in their role of fighting disease and infection. Blood contains platelets which are essential for clotting the blood, which occurs follwing an injury to stop blood loss. Blood also carries waste products, such as Carbon Dioxide away from muscles and organs in order to be dispelled by the lungs.

Systemic & pulmonary circulation

There are three circulatory processes occurring simultaneously within the body. Firstly systemic circulation carries blood around the body, pulmonary circulation carries blood to the lungs and coronary circulation provides the heart with its own supply of blood.

At the start of the blood circulatory cycle the heart pumps oxygenated blood out of the left ventricle, through the Aorta (the largest artery in the body). The aorta divides into smaller arteries, then arterioles and finally into microscopic capillaries, found deep within muscles and organs. Here the Oxygen (and other nutrients) passes through the thin capillary walls, into the tissues where it can be used to produce the energy muscles require to contract.

A waste product of energy production (metabolism) is Carbon dioxide and in order to be removed, it too passes across the walls of the capillaries, into the blood stream. The blood continues back towards the heart, through venules and then veins, into the right atrium.

Once blood returns to the heart it is then pumped from the right ventricle through the Pulmonary arteries to the lungs, where the waste carbon dioxide can be expelled and more Oxygen collected. The Pulmonary vein carries oxygenated blood back to the left atrium of the heart, where the cycle starts again.

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