vénules

Vénules are very small veins that collect deoxygenated blood from capillaries. They are the smallest venous structures in the body, forming a network that gradually merges into larger veins as they approach the heart. Vénules play a crucial role in the circulatory system by serving as the initial collecting points for blood returning from the tissues.

The walls of vénules are thin, consisting of a tunica intima, tunica media, and tunica externa. Unlike arteries, the tunica media in vénules is less developed, containing fewer smooth muscle cells and elastic fibers. This structural characteristic reflects their role in low-pressure blood return. The diameter of vénules typically ranges from 10 to 100 micrometers, though some postcapillary vénules can be as small as 10-30 micrometers.

Vénules are significant sites for various physiological and pathological processes. For instance, they are important in the inflammatory response. During inflammation, chemical mediators cause vénular walls to become more permeable, allowing plasma and white blood cells to leak into the surrounding tissue, a process known as diapedesis. This increased permeability is a hallmark of the early stages of inflammation. Furthermore, vénules are also involved in thermoregulation, as their diameter can be adjusted to control blood flow near the skin surface. Certain medical conditions and treatments can affect vénules, highlighting their importance in overall vascular health.