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endothelium
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{{about|the lining of blood and lymphatic vessels|the endothelium of the cornea|corneal endothelium}}







factoids
Endothelium refers to cells that line the interior surface of blood vessels and lymphatic vessels,{{DorlandsDict|three/000035470|Endothelium}} forming an interface between circulating blood or lymph in the lumen and the rest of the vessel wall. It is a thin layer of simple, or single-layered, squamous cells called endothelial cells. Endothelial cells in direct contact with blood are called vascular endothelial cells, whereas those in direct contact with lymph are known as lymphatic endothelial cells.Vascular endothelial cells line the entire circulatory system, from the heart to the smallest capillaries. These cells have unique functions in vascular biology. These functions include fluid filtration, such as in the glomerulus of the kidney, blood vessel tone, hemostasis, neutrophil recruitment, and hormone trafficking. Endothelium of the interior surfaces of the heart chambers is called endocardium.

Structure

Endothelium is mesodermal in origin. Both blood and lymphatic capillaries are composed of a single layer of endothelial cells called a monolayer. In straight sections of a blood vessel, vascular endothelial cells typically align and elongate in the direction of fluid flow.JOURNAL, Eskin SG, Ives CL, McIntire LV, Navarro LT, Response of cultured endothelial cells to steady flow, Microvascular Research, 28, 1, 87–94, July 1984, 6748961, 10.1016/0026-2862(84)90031-1, JOURNAL, Langille BL, Adamson SL, Relationship between blood flow direction and endothelial cell orientation at arterial branch sites in rabbits and mice, Circulation Research, 48, 4, 481–8, April 1981, 7460219, 10.1161/01.RES.48.4.481,

Terminology

The foundational model of anatomy makes a distinction between endothelial cells and epithelial cells on the basis of which tissues they develop from, and states that the presence of vimentin rather than keratin filaments separate these from epithelial cells.WEB,weblink Endothelial cell, BioPortal, Stanford University, 2013-09-28, yes,weblink" title="web.archive.org/web/20131002075249weblink">weblink 2013-10-02, Many considered the endothelium a specialized epithelial tissue.JOURNAL, Kovacic JC, Mercader N, Torres M, Boehm M, Fuster V, Epithelial-to-mesenchymal and endothelial-to-mesenchymal transition: from cardiovascular development to disease, Circulation, 125, 14, 1795–808, April 2012, 22492947, 3333843, 10.1161/circulationaha.111.040352,

Function

(File:2104 Three Major Capillary Types.jpg|thumbnail|Endothelium lines the inner wall of vessels, shown here.)Endothelial cells are involved in many aspects of vascular biology, including:
  • Barrier function - the endothelium acts as a semi-selective barrier between the vessel lumen and surrounding tissue, controlling the passage of materials and the transit of white blood cells into and out of the bloodstream. Excessive or prolonged increases in permeability of the endothelial monolayer, as in cases of chronic inflammation, may lead to tissue edema/swelling.
  • Blood clotting (thrombosis & fibrinolysis). The endothelium normally provides a non-thrombogenic surface because it contains, for example, heparan sulfate which acts as a cofactor for activating antithrombin, a protease that inactivates several factors in the coagulation cascade.
  • InflammationJOURNAL, Li X, Fang P, Li Y, Kuo YM, Andrews AJ, Nanayakkara G, Johnson C, Fu H, Shan H, Du F, Hoffman NE, Yu D, Eguchi S, Madesh M, Koch WJ, Sun J, Jiang X, Wang H, Yang X, Mitochondrial Reactive Oxygen Species Mediate Lysophosphatidylcholine-Induced Endothelial Cell Activation, Arteriosclerosis, Thrombosis, and Vascular Biology, 36, 6, 1090–100, June 2016, 27127201, 4882253, 10.1161/ATVBAHA.115.306964,
  • Formation of new blood vessels (angiogenesis)
  • Vasoconstriction and vasodilation, and hence the control of blood pressure
  • Repair of damaged or diseased organs via an injection of blood vessel cellsNEWS,weblink Blood vessel cells can repair, regenerate organs, scientists say, 2018-11-13,
  • Angiopoietin-2 works with VEGF to facilitate cell proliferation and migration of endothelial cells
Angiogenesis is a crucial process for embryonic and fetal development and organ growthJOURNAL, Bouïs D, Kusumanto Y, Meijer C, Mulder NH, Hospers GA, A review on pro- and anti-angiogenic factors as targets of clinical intervention, Pharmacological Research, 53, 2, 89–103, February 2006, 16321545, 10.1016/j.phrs.2005.10.006, . The process is triggered by tissue hypoxia or insufficient oxygen tension leading to the new development of blood vessels lined with endothelial cells. Angiogenesis is a tightly regulated event that is balanced by pro- and antiangiogenic signals including integrins, chemokines, angiopoietins, oxygen sensing agents, junctional molecules and endogenous inhibitors.JOURNAL, Bouïs D, Kusumanto Y, Meijer C, Mulder NH, Hospers GA, A review on pro- and anti-angiogenic factors as targets of clinical intervention, Pharmacological Research, 53, 2, 89–103, February 2006, 16321545, 10.1016/j.phrs.2005.10.006, The general outline of the process is
  • activating signals binding to surface receptors of vascular endothelial cells.
  • activated endothelial cells release proteases leading to the degradation of the basement membrane
  • endothelial cells are freed to migrate from the existing blood vessels and begin to proliferateto forming extensions towards the source of the angiogenic stimulus.

Clinical significance

Endothelial dysfunction, or the loss of proper endothelial function, is a hallmark for vascular diseases, and is often regarded as a key early event in the development of atherosclerosis. Impaired endothelial function, causing hypertension and thrombosis, is often seen in patients with coronary artery disease, diabetes mellitus, hypertension, hypercholesterolemia, as well as in smokers. Endothelial dysfunction has also been shown to be predictive of future adverse cardiovascular events, and is also present in inflammatory disease such as rheumatoid arthritis and systemic lupus erythematosus. Endothelial dysfunction is a result of changes in endothelial physiologyJOURNAL, Iantorno M, Campia U, Di Daniele N, Nistico S, Forleo GB, Cardillo C, Tesauro M, Obesity, inflammation and endothelial dysfunction, Journal of Biological Regulators and Homeostatic Agents, 28, 2, 169–76, April 2014, 25001649, JOURNAL, Reriani MK, Lerman LO, Lerman A, Endothelial function as a functional expression of cardiovascular risk factors, Biomarkers in Medicine, 4, 3, 351–60, June 2010, 20550469, 2911781, 10.2217/bmm.10.61, . In response to lipid accumulation and proinflammatory stimuli, endothelial cells become activated, which is characterized by the expression of adhesion molecules such as E-selectin, VCAM-1 and ICAM-1JOURNAL, Lopez-Garcia E, Hu FB, Nutrition and the endothelium, Current Diabetes Reports, 4, 4, 253–9, August 2004, 15265466, . Additionally, transcription factors including AP-1 and NF-κB  become activated, leading to up-regulated expression of proinflammatory cytokines, such as IL-1, TNFα and IFNγJOURNAL, Blake GJ, Ridker PM, Inflammatory bio-markers and cardiovascular risk prediction, Journal of Internal Medicine, 252, 4, 283–94, October 2002, 12366601, JOURNAL, Mizuno Y, Jacob RF, Mason RP, Inflammation and the development of atherosclerosis, Journal of Atherosclerosis and Thrombosis, 18, 5, 351–8, 2011, 21427505, . The proatherogenic profile expressed by the endothelial cells promotes accumulation of lipids and lipoproteins in the intima, and subsequent recruitment of leukocytes and platelets, as well as proliferation of smooth muscle cells, leading to fatty streak formation. The lesions formed in the intima, and persistent inflammation lead to desquamation of endothelium, which disrupts the endothelial barrier, leading to injury and consequent dysfunctionJOURNAL, Mäyränpää MI, Heikkilä HM, Lindstedt KA, Walls AF, Kovanen PT, Desquamation of human coronary artery endothelium by human mast cell proteases: implications for plaque erosion, Coronary Artery Disease, 17, 7, 611–21, November 2006, 17047445, 10.1097/01.mca.0000224420.67304.4d, . One of the main mechanisms of endothelial dysfunction is the diminishing of nitric oxide, often due to high levels of asymmetric dimethylarginine, which interfere with the normal L-arginine-stimulated nitric oxide synthesis and so leads to hypertension. The most prevailing mechanism of endothelial dysfunction is an increase in reactive oxygen species, which can impair nitric oxide production and activity via several mechanisms.JOURNAL, Deanfield J, Donald A, Ferri C, Giannattasio C, Halcox J, Halligan S, Lerman A, Mancia G, Oliver JJ, Pessina AC, Rizzoni D, Rossi GP, Salvetti A, Schiffrin EL, Taddei S, Webb DJ, Endothelial function and dysfunction. Part I: Methodological issues for assessment in the different vascular beds: a statement by the Working Group on Endothelin and Endothelial Factors of the European Society of Hypertension, Journal of Hypertension, 23, 1, 7–17, January 2005, 15643116, 10.1097/00004872-200501000-00004, The signalling protein ERK5 is essential for maintaining normal endothelial cell function.JOURNAL, Roberts OL, Holmes K, Müller J, Cross DA, Cross MJ, ERK5 and the regulation of endothelial cell function, Biochemical Society Transactions, 37, Pt 6, 1254–9, December 2009, 19909257, 10.1042/BST0371254, A further consequence of damage to the endothelium is the release of pathological quantities of von Willebrand factor, which promote platelet aggregation and adhesion to the subendothelium, and thus the formation of potentially fatal thrombi.In cancer therapy the development and delivery of anti-angiogenic drugs is a very promising path and restoring vascular homeostasis holds great potential for the treatment of ischemic tissue diseases JOURNAL, Van Hove AH, Benoit DS, Depot-Based Delivery Systems for Pro-Angiogenic Peptides: A Review, Frontiers in Bioengineering and Biotechnology, 3, 102, 2015, 26236708, 4504170, 10.3389/fbioe.2015.00102,

See also

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References

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External links

{{Epithelium and epithelial tissue}}{{Cardiovascular system}}{{Authority control}}

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