Venule

Venule

Diagram showing venules and capillaries

A venule is a small blood vessel in the microcirculation that allows blood to return from the capillaries to the larger veins. Venules are an essential component of the circulatory system, playing a critical role in the return of deoxygenated 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: the inner endothelium, a middle layer of smooth muscle, and an outer layer of connective tissue. The structure of venules is similar to that of veins, but they are smaller and have thinner walls.

Function

Venules serve as conduits for blood returning to the heart. They collect blood from the capillary beds and transport it to the veins. Venules also play a role in the immune system, as they are sites where white blood cells can exit the bloodstream to reach tissues.

Clinical significance

Venules can be involved in various medical conditions. For example, inflammation can cause venules to become more permeable, leading to edema. In some diseases, such as vasculitis, venules can become inflamed and damaged.

Related pages

• Vein
• Capillary
• Artery
• Microcirculation

References

• Guyton, Arthur C.; Hall, John E. (2006). Textbook of Medical Physiology. Elsevier Saunders. ISBN 978-0-7216-0240-0.
• "Venule." Encyclopædia Britannica. Encyclopædia Britannica Online.