Artery and vein. Light micrograph of a cross- section of a human artery and a longitudinal section of a vein. The artery (at left, purple) surrounds a central cavity (blue). The artery's corrugated inner surface layer (internal elastic lamina) is comprised of an elastic protein (elastin, purple). Surrounding is a layer of smooth muscle. Arteries carry blood from the heart to the rest of the body, and so must withstand high pressure blood. The vein (purple, at right) is filled with rounded blood cells. This vessel has thin walls because it carries low-pressure blood from the body to the heart. Magnification: x160 at 35mm size.
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