Blood vessels

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Blood vessels are hollow organs that transport blood throughout the body and supply it with oxygen and nutrients. The inner cavity in which the blood flows is called the lumen and is typically surrounded by one or more layers, depending on the type of blood vessel.

The wall of larger vessels such as arteries and veins consists of three layers. The innermost layer is the tunica intima, which is made up of endothelial cells and a subendothelial connective tissue layer. The middle layer, the tunica media, consists of smooth muscle cells and partly elastic and collagenous connective tissue. Arteries have a more pronounced tunica media which gives them less compliance than veins. The outermost tunica externa or adventitia is a layer of connective tissue that anchors the vessel in its surroundings.

Small vessels such as arterioles, venules and capillaries all contribute to microcirculation. These vessels have thinner wall layers, which, for example, in capillaries only consist of a layer of endothelial cells, the basal lamina and pericytes.

Watch the following videos to learn more about blood vessel microanatomy:

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