Circulation

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The circulatory system is the specialized transport system that carries materials quickly through the body. It is needed because simple diffusion and osmosis are too slow for large multicellular organ…

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The heart is located between the lungs and is protected by the rib cage. It is approximately the size of a fist.

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The human heart has four chambers: two atria and two ventricles. The upper chambers are atria, and the lower chambers are ventricles.

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The ventricles have thicker walls because they pump blood out of the heart with greater force. The atria only push blood into the ventricles, so their walls are thinner.

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The pericardium is a two-layered membrane that covers the heart. The space between its layers contains pericardial fluid, which protects the heart from shocks.

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Coronary vessels are the blood vessels in the walls of the heart. They supply blood to the heart muscles.

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Arteries are blood vessels that originate from the heart and supply blood to various organs in the body. They have thick walls. The aorta is the largest artery.

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Veins are blood vessels that bring blood from all body parts to the heart. They have relatively thin walls. Valves in veins help prevent backflow of blood.