Corpus: Venule

Venule is also called a small vein.

The venules collect the blood from the venous leg of the capillary bed and unite with neighbouring venules to form veins. The wall structure of the venules is comparable to that of the veins, but changes slightly along the course of the vessel.

The part of a venule facing the capillary bed has almost no tunica media. This means that venules, like capillaries, can exchange fluid with the surrounding tissue. They have a high vascular permeability. In the further course of the vessel, the venule has a thin tunica media made of smooth muscle. In contrast to veins, venules do not have venous valves.

In lymph nodes, tonsil tissue and lymph follicles, a special form of venules is found that have a high endothelium through which lymphocytes can migrate into the parenchyma. These venules are referred to as postcapillary venules or high endothelial venules (HEV).