Venules

Venules are very small blood vessels 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 formed when capillary beds unite. They drain blood from the capillaries into the veins, hence acting as a bridge between these two components of the blood vessel system. They are variously classified above capillaries, and they can further unite to form veins.

Postcapillary venules

Postcapillary venules are the smallest venules and drain blood from the capillaries directly. They are a location of much immune system action and communication.

Collecting venules

Collecting venules receive blood from multiple postcapillary venules and pass it on to larger venules.

Muscular venules

Muscular venules receive blood from the collecting venules and deliver it to the veins. They have a tunica media with one or two layers of smooth muscle.

Function

Venules, like other blood vessels, play a crucial role in maintaining the body's homeostasis. They help return deoxygenated blood from the body's tissues back to the heart. They also play a key role in the immune response, as they allow white blood cells to move from the bloodstream into the surrounding tissues.

Clinical significance

Venules can be affected by a variety of medical conditions. Inflammation of the venules, known as vasculitis, can lead to serious health problems such as organ damage. Other conditions, such as varicose veins, can also affect the venules.

See also

• Blood vessels
• Capillaries
• Veins
• Vasculitis
• Varicose veins

Venules Resources
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