vénule

A vénule is a small vein that collects deoxygenated blood from capillaries. These tiny vessels are the smallest components of the venous system, forming a network that gradually merges into larger veins. Vénules play a crucial role in the circulatory system by transporting blood away from the body's tissues and back towards the heart.

The structure of a vénule is relatively simple, consisting of a thin wall made up of an inner endothelial lining, a layer of connective tissue, and sometimes a small amount of smooth muscle. Unlike arteries, vénules have thinner walls and less elastic tissue because the blood pressure within them is significantly lower. This lower pressure is a result of the blood passing through the narrow capillaries, where resistance slows the flow.

The function of vénules is primarily to act as conduits for blood returning from the capillary beds. As blood flows from capillaries into vénules, it begins its journey back to the heart. This collected blood is deoxygenated, meaning it has delivered its oxygen and nutrients to the surrounding cells and has picked up carbon dioxide and waste products. The merging of multiple vénules forms larger veins, which eventually lead to the major venous trunks.

In certain physiological processes, such as inflammation, vénules exhibit increased permeability. This allows plasma and leukocytes (white blood cells) to move from the bloodstream into the surrounding tissue, which is a key part of the immune response. The ability of vénules to facilitate this extravasation is critical for combating infection and initiating tissue repair.