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The Circulatory System refers to the flow and control of the blood around the body.In humans the system runs like this: Heart>Artery>Arteriole>Capillary>Venule>Vein>Heart. As blood begins to circulate, it leaves the heart from the left ventricle and goes into the aorta, the largest artery in the body. The oxygenated blood leaving the aorta travels throughout the body in its system of arteries into the smallest arterioles. On its way back to heart, the blood travels through a system of veins. As it reaches the lungs, the carbon dioxide which is a waste product is removed from the blood and replaced with fresh oxygen that we have inhaled through the lungs. Blood that comes from the left side of the heart is full of oxygen and nutirients like protein, fat, carbohydrates, vitamins, and minerals.This blood in systemic arteries, full of oxygen and nutrients, is systemic arterial blood.
The biggest systemic artery in the body is the aorta, the large blood vessel that comes out of the heart. Smaller arteries branch off from the aorta. These arteries have further smaller arteries that branch off from them. The smallest arteries turn into arterioles.
The smallest blood vessels are capillaries. Systemic arterioles turn into capillaries. The blood from arterioles goes into the capillaries. There oxygen and nutrients go out of the blood into the tissue around the capillaries. The blood also picks up carbon dioxide and waste from the tissue. Venules are the smallest veins that drain deoxygenated blood from the capillary bed to the veins.Veins take blood back to the heart. As veins go back to the heart, they get bigger. The biggest systemic veins in the body are the vena cava. There are two vena cava: the inferior vena cavatakes blood from the lower part of the body to the right side of the heart, and the superior vena cava takes blood from the upper part of the body to the heart.
Most of the cells in the human body are not in direct contact with the external environment, so rely on the circulatory system to act as a transport service for them. The blood, heart, and blood vessels form the Cardiovascular System. The lymph, lymph nodes and lymph vessels form the Lymphatic System. The Cardiovascular System and the Lymphatic System collectively make up the Circulatory System.
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