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| CAPILLARIES Capillaries are tiny blood vessels that pass blood from the arteries into the veins. They are very small, the largest being about 10 micrometers in diameter. Their walls are thin which allows materials to pass into the capillaries. Different types of capillaries exist and perform different functions for the body. Primarily, however, the capillaries are able to profuse the tissues of the body with needed oxygen and important nutrients supplied by blood.
Continuous capillaries have the thickest endothelial wall. They allow only water, and ions into their pathways. Fenestrated capillaries have “windows” that lets larger molecules in and out of the capillaries. Sinusoidal capillaries have the greatest amount of permeability, letting red blood cells and proteins in through the endothelial walls. The function of the capillaries is "communicators" between arteries and veins, they also are the tiny blood vessels that supply blood to organs. Capillaries supplying blood to an organ, when taken in whole, are called a capillary bed. They are numerous, and feed the organ with amino acids, proteins, and most importantly oxygen, without which organ cells could not survive. |