View source for Venule

{{Infobox Vein |
Name         = {{PAGENAME}} |
Latin        = venula  |
GraySubject  = |
GrayPage     = |
Image        = Illu_capillary.jpg |
Caption      = Illustration of capillary |
Image2       = |
Caption2     = |
Precursor    = |
System       = |
Artery       = |
Vein         = |
Nerve        = |
Lymph        = |
MeshName     = |
MeshNumber   = |
}}
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 [[vein]]s. Venules range from 8 to 100μm in diameter and are formed when capillaries unite.

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 [[Endothelium|endothelial cell]]s that act as a [[biological membrane|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]]. They are extremely porous so that fluid and blood cells can move easily from the bloodstream through their walls.

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, using the beta form of semi-red blood cells and white blood cells to form.

==External links==
* {{MeshNumber|A07.231.432.952|Venules}}

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{{Cardiovascular_system}}

[[Category:Cardiovascular system]]

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[[ru:Венулы]]
[[ja:細静脈]]
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