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Cross section of vein

Arteries and veins have the same layers of tissues in their walls, but the proportions of these layers differ. Lining the core of each is a thin layer of endothelium, and covering each is a sheath of connective tissue, but an artery has thick intermediate layers of elastic and muscular fiber while in the vein, these are much thinner and less developed. With the exception of pulmonary and umbilical veins and arteries, arteries carry oxygenated blood from the heart, while veins return CONTINUE SCROLLING TO READ MORE BELOW...