Venule 619442 222538595 2008-06-29T21:54:09Z Udo.schroeter 7128480 [[Image:Illu_capillary.jpg|thumb|300px]] A '''venule''' is a small [[blood vessel]] that allows deoxygenated [[blood]] to return from the [[capillary]] beds to the larger blood vessels called [[vein]]s. 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]]. These vessels are pink sometimes due to the high content of nitrogen. 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. ==External links== * {{MeshNumber|A07.231.432.952|Venules}} {{circulatory-stub}} {{Cardiovascular_system}} [[Category:Cardiovascular system]] [[bs:Venula]] [[de:Venole]] [[es:Vénula]] [[it:Venula]] [[nds:Venool]] [[pt:Vénula]] [[ru:Венулы]]