verisuonikerrokset

Verisuonikerrokset, also known as vascular layers or tunics, refer to the distinct layers that make up the wall of blood vessels, including arteries, veins, and capillaries. These layers provide structural integrity, regulate blood flow, and facilitate exchange of substances. The three primary layers are the tunica intima, tunica media, and tunica externa.

The tunica intima is the innermost layer, lining the lumen of the blood vessel. It consists of a single layer of endothelial cells, which are smooth and flat, minimizing friction as blood flows. Beneath the endothelium lies a basement membrane and a subendothelial connective tissue layer. In arteries, this layer also contains an internal elastic lamina.

The tunica media is the middle and typically the thickest layer. It is composed primarily of smooth muscle cells and elastic fibers. The smooth muscle allows for vasoconstriction and vasodilation, regulating blood pressure and flow. The elastic fibers help maintain vessel shape and recoil after stretching. The composition and thickness of the tunica media vary depending on the type of blood vessel; arteries have a thicker tunica media than veins due to the higher pressures they withstand.

The tunica externa, or tunica adventitia, is the outermost layer. It is made of connective tissue, primarily collagen and elastic fibers, which anchor the blood vessel to surrounding tissues. This layer provides structural support and protection. In larger blood vessels, the tunica externa also contains vasa vasorum, small blood vessels that supply nutrients to the vessel wall itself. Capillaries, being very small, consist only of a tunica intima.