Venule

Venule

Diagram of capillaries connecting to venules

A venule is a small blood vessel in the microcirculation that allows deoxygenated blood to return from the capillary beds to the larger blood vessels called veins. Venules are an essential component of the circulatory system, playing a crucial role in the return of blood to the heart.

Structure

Venules are formed when capillaries come together. They are typically 7 to 50 micrometers in diameter. The walls of venules are composed of three layers, similar to larger veins, but they are much thinner. These layers include:

• The tunica intima, which is the innermost layer and consists of a thin layer of endothelial cells.
• The tunica media, which is the middle layer and contains a small amount of smooth muscle.
• The tunica externa (or adventitia), which is the outermost layer and is made up of connective tissue.

Function

File:Venule.jpg

Illustration of a venule

Venules serve as the site where blood from the capillaries is collected and transported back to the veins. They play a key role in the exchange of nutrients and waste products between the blood and tissues. The permeability of venules allows for the movement of white blood cells into tissues during inflammatory responses.

Clinical significance

Venules can be involved in various medical conditions. For example, inflammation can cause venules to become more permeable, leading to edema. In certain diseases, such as vasculitis, the walls of venules can become inflamed, which can lead to tissue damage.

Related pages

• Vein
• Capillary
• Arteriole
• Microcirculation