# Venule > Mediated Wiki article. Canonical URL: https://mediated.wiki/source/Venule > Markdown URL: https://mediated.wiki/source/Venule.md > Source: https://en.wikipedia.org/wiki/Venule > Source revision: 1315474663 > License: Creative Commons Attribution-ShareAlike 4.0 International (https://creativecommons.org/licenses/by-sa/4.0/) Very small blood vessel in the microcirculation Blood vessel Venule Types of blood vessels, including a venule, vein, and capillaries Details Identifiers Latin venula MeSH D014699 TA98 A12.0.00.037 TA2 3903 TH H3.09.02.0.03002 FMA 63130 Anatomical terminology [edit on Wikidata] A **venule** is a very small [vein](/source/Vein) in the [microcirculation](/source/Microcirculation) that allows [blood](/source/Blood) to return from the [capillary beds](/source/Capillary_beds) to drain into the [venous system](/source/Venous_system) via increasingly larger veins. **Post-capillary venules** are the smallest of the veins with a diameter of between 10 and 30 [micrometres](/source/Micrometre) (μm). When the post-capillary venules increase in diameter to 50 μm they can incorporate smooth muscle and are known as **muscular venules**.[1] Veins contain approximately 70% of total blood volume, while about 25% is contained in the venules.[2] Many venules unite to form a vein. ## Structure This section needs more reliable medical references for verification or relies too heavily on primary sources. Please review the contents of the section and add the appropriate references if you can. Unsourced or poorly sourced material may be challenged and removed. Find sources: "Venule" – news · newspapers · books · scholar · JSTOR (April 2018) Post-capillary venules have a single layer of endothelium surrounded by a [basal lamina](/source/Basal_lamina). Their size is between 10 and 30 micrometers and are too small to contain smooth muscle. They are instead supported by [pericytes](/source/Pericyte) that wrap around them.[1] When the post-capillary venules increase in diameter to 50 μm they can incorporate smooth muscle and are known as **muscular venules**.[1] They have an inner [endothelium](/source/Endothelium) composed of squamous [endothelial cells](/source/Endothelium) that act as a [membrane](/source/Biological_membrane), a middle layer of muscle and elastic tissue and an outer layer of [fibrous connective tissue](/source/Fibrous_connective_tissue). The middle layer is poorly developed so that venules have thinner walls than [arterioles](/source/Arterioles). They are porous so that fluid and blood cells can move easily from the bloodstream through their walls. Short [portal venules](/source/Hypophyseal_portal_system) between the [posterior pituitary](/source/Posterior_pituitary) and the [anterior pituitary](/source/Anterior_pituitary) lobes provide an avenue for rapid hormonal exchange via the blood.[3] Specifically within and between the pituitary lobes is anatomical evidence for confluent interlobe venules providing blood from the anterior to the neural lobe that would facilitate moment-to-moment sharing of information between lobes of the pituitary gland.[3] In contrast to regular venules, [high endothelial venules](/source/High_endothelial_venules) are a special type of venule where the endothelium is made up of [simple cuboidal](/source/Simple_cuboidal) cells. [Lymphocytes](/source/Lymphocyte) exit the blood stream and enter the lymph nodes via these specialized venules when an infection is detected. Compared with arterioles, the venules are larger with much weaker muscular coat. They are the smallest united common branch in the human body. ## See also - [Arteriole](/source/Arteriole) - [Surface chemistry of microvasculature](/source/Surface_chemistry_of_microvasculature) - [Microcirculation](/source/Microcirculation) ## References 1. ^ [***a***](#cite_ref-GRAYS2016_1-0) [***b***](#cite_ref-GRAYS2016_1-1) [***c***](#cite_ref-GRAYS2016_1-2) Standring, Susan (2016). *Gray's anatomy : the anatomical basis of clinical practice* (Forty-first ed.). [Philadelphia]. p. 131. [ISBN](/source/ISBN_(identifier)) [9780702052309](https://en.wikipedia.org/wiki/Special:BookSources/9780702052309).{{[cite book](https://en.wikipedia.org/wiki/Template:Cite_book)}}: CS1 maint: location missing publisher ([link](https://en.wikipedia.org/wiki/Category:CS1_maint:_location_missing_publisher)) 1. **[^](#cite_ref-2)** Woods, Susan (2010). *Cardiac Nursing*. New York: Lippincotts. p. 955. [ISBN](/source/ISBN_(identifier)) [9780781792806](https://en.wikipedia.org/wiki/Special:BookSources/9780781792806). 1. ^ [***a***](#cite_ref-gross_3-0) [***b***](#cite_ref-gross_3-1) Gross, PM; Joneja, MG; Pang, JJ; Polischuk, TM; Shaver, SW; Wainman, DS (1993). "Topography of short portal vessels in the rat pituitary gland: A scanning electron-microscopic and morphometric study of corrosion cast replicas". *Cell and Tissue Research*. **272** (1): 79–88. [doi](/source/Doi_(identifier)):[10.1007/bf00323573](https://doi.org/10.1007%2Fbf00323573). [PMID](/source/PMID_(identifier)) [8481959](https://pubmed.ncbi.nlm.nih.gov/8481959). [S2CID](/source/S2CID_(identifier)) [23657199](https://api.semanticscholar.org/CorpusID:23657199). ## External links v t e Arteries and veins Vessels Arteries Nutrient artery Arteriole Metarteriole Elastic artery Capillaries Types Continuous Fenestrated Sinusoidal Precapillary sphincter Precapillary resistance Veins Vena comitans Superficial vein Deep vein Perforator vein Emissary veins Venous plexus Venule Lymph Lymphatic vessel Lymph Lymph capillary Circulatory system Systemic Left heart → Aorta → Arteries → Arterioles → Capillaries → Venules → Veins → Vena cava → (Right heart) Pulmonary Right heart → Pulmonary arteries → Lungs → Pulmonary vein → (Left heart) Microanatomy Microvessel Microcirculation Tunica intima Endothelium Internal elastic lamina Tunica media Tunica externa Vasa vasorum Vasa nervorum Vascular nerves Rete mirabile Circulatory anastomosis Authority control databases International GND Other Terminologia Anatomica --- Adapted from the Wikipedia article [Venule](https://en.wikipedia.org/wiki/Venule) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Venule?action=history)). 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