venule

[Latin vēnula, diminutive of vēna, vein.]

The smallest of the venous blood vessels; consists of an endothelial tube enclosed in a variable amount of elastic and collagenous tissue. Smooth muscle is introduced in the media as the caliber of the vessel increases. The muscle fibers are distributed sparsely in the smaller vessels but coalesce into circumferential bands in the larger vessels.

A small vein that, unlike a capillary, has some connective tissue in its wall.

Any of the small vessels that collect blood from the capillary plexuses and join to form veins.

Vein: Venule
Illustration of capillary
Latin	venula

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 blood vessels that drain blood directly from the capillary beds. Many venules unite to form a vein.

Structure

Venule walls have three layers: An inner endothelium composed of squamous endothelial cells that act as a membrane, a middle layer of muscle and elastic tissue and an outer layer of fibrous connective tissue. The middle layer is poorly developed so that venules have thinner walls than arterioles.

In contrast to regular venules, high endothelial venules are a special type of venule where the endothelium is made up of simple cuboidal cells. Lymphocytes re-enter the bloodstream through the HEVs.

They form from anastomosis of capillaries.

External links

• MeSH A07.231.432.952

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v • d • e Circulatory system: Arteries and veins (TA A12.2-3, GA 6.543/GA 7.641) Systemic circulation (Heart ) → Aorta → Arteries → Arterioles → Capillaries → Venules → Veins → Vena cava → (Heart) Pulmonary circulation (Heart) → Pulmonary arteries → (Lungs) → Pulmonary vein → (Heart) Blood vessels Endothelium · Tunica intima · Tunica media · Tunica externa Vasa vasorum · Vasa nervorum Rete mirabile · Arteriovenous anastomosis Arteries Nutrient artery Veins Vena comitans · Superficial vein · Deep vein · Emissary veins vascular navs: anat/physio/dev, noncongen/systemic vasculitis/congen/neoplasia, symptoms+signs/eponymous, proc

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