Blood Vessels
About the Blood Vessels
The circulatory system has approximately 100,000 km of blood vessels. Arteries carry blood away from the heart, with thick walls of smooth muscle and elastic tissue to withstand high pressure. The aorta is the largest artery, originating from the left ventricle. Arterioles regulate blood flow through constriction and dilation. Capillaries are one cell thick, allowing gas, nutrient, and waste exchange via diffusion. Starling forces hydrostatic and oncotic pressure govern fluid movement. Venules and veins return blood to the heart, with valves preventing backflow in the legs. Varicose veins occur when valves fail. The portal venous system carries nutrient rich blood from the GI tract to the liver. Endothelium lines all vessels, producing nitric oxide for vasodilation.
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