Venule

Venule

A venule is a very small blood vessel in the microcirculation that allows blood to return from the capillary beds to the larger blood vessels called veins. Venules range from 7 to 50μm in diameter. Veins contain approximately 70% of total blood volume, 25% of which is contained in the venules.

Structure

Venules are the smallest branches of the venous system. They receive blood from the capillaries and deliver it to the larger blood vessels, the veins. The primary function of the venules, similar to the veins, is to return blood to the heart.

Function

Venules are responsible for draining oxygen-depleted blood from the capillary beds and returning it to the larger veins, which will eventually return the blood to the heart. They also play a key role in the immune system: the walls of the venules are specialized to allow white blood cells (leukocytes) to pass through them, in a process known as leukocyte extravasation.

Clinical significance

Inflammation of the venules, a condition known as venulitis, can be caused by several conditions including autoimmune disorders, infections, and allergies. It can result in redness, swelling, and pain in the affected area.

See also

• Capillary
• Vein
• Blood vessel
• Microcirculation

References

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