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They comprise of three layers; inner, middle, and outer.

In the center of the vessel, there is the lumen, which carries the blood. In an artery the lumen is smaller, and in a vein it is much larger.

The tunica intema is the inner layer, and it is made up of the endothelium (the lining of the vessel), specifically squamous epithilium.

The tunica media is the layer of elastic fibres and smooth muscle which allow the lumen to shrink (vasoconstriction) and dilate (vasodilation).

The tunica externa is a layer of collagen. It is the strong part of the vessel, as collagen is a fibrous protein and insoluble in water.

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14y ago

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