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Blood vessels - arteries, veins capillaries, and their functions

Definition of blood vessels: The blood vessels of the circulatory system act as pipes (tubes) through which the blood flow. there are three types of blood vessels in the human body. they are :
  1. Arteries,
  2. Veins, and
  3. Capillaries.

The function of Arteries:

The arteries: arteries carry the oxygen-rich blood (oxygenated) blood away from the heart to various organs of the human body. the main artery of the body that originates in the left ventricle of the heart is called the aorta. it is the largest artery in our body. the main artery carries oxygenated blood from the left ventricle to all the parts of the body. the heart sends impure blood to the lungs through an artery called the pulmonary artery. this is the only artery that carries impure blood (deoxygenated blood). the pulmonary artery is connected to the right ventricle of the heart. arteries have thick and elastic walls because blood emerges from the heart under high pressure.

The function of  veins:

The veins: the walls of a vein are thin because the blood flow of them slow.they have valves that ensure the blood flow only one direction. the pulmonary vein is connected to the left atrium of the heart. the main vein carries deoxygenated blood from all parts of the body to the heart. the heart receives pure oxygen-rich blood (oxygenated) through the pulmonary vein. this is the only vein that carries oxygenated blood.

The function of  capillaries:

The capillaries: the capillaries are thin-walled tubes or blood vessels which connect arteries and veins. all living cell of the human body is close to the capillary. the walls of capillaries are only one cell thick. the various dissolved substances present in the blood pass into the cells through the thin walls of the capillaries at the same time the waste substances enter into the capillaries. the other end of the capillaries connects to the veins.

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