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Saturday, 12 January 2019

Arteries, Veins and Capillaries

 Arteries receive blood directly from the heart. To withstand the high pressure of the blood that flows in them, they have thick walls which are muscular and elastic. These walls also enable arteries to constrict or dilate, and thus regulate the amount of blood flowing in them.

     Veins carry blood back to the heart. The blood in them is at low pressure. Thus, the wall of a vein is not as thick, muscular or elastic as that of an artery of about the same size. Most veins have valves inside them to prevent back flow of blood. The flow of blood along veins is assisted by the movements of the skeletal muscles.

     Capillaries are microscopic blood vessels that form a network linking arterioles to venules. The blood in the capillaries at the arteriole end is at a higher pressure than at the venules end capillaries are the most numerous blood vessels in the body. Their large numbers and one cell thick walls enable them to provide a large surface area through which materials can be exchanged between the blood and the body cells.  
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