Blood vessel 48530 224980623 2008-07-11T08:22:13Z Closedmouth 372693 Reverted edits by [[Special:Contributions/203.213.205.139|203.213.205.139]] to last version by SarekOfVulcan (using [[WP:HG|Huggle]]) [[Image:Arteriessystem.png|200px|right|framed|The arterial system]] The '''blood vessels''' are part of the [[circulatory system]] and function to transport [[blood]] throughout the body. The most important vessels in the system are the [[capillary|capillaries]], the microscopic vessels which enable the actual exchange of water and chemicals between the blood and the tissues, while the conduit vessels, [[artery|arteries]] and [[vein]]s, carry blood away from the heart and through the capillaries or back towards the [[heart]], respectively. == Anatomy == The arteries and veins have the same basic structure. There are three layers, from inside to outside while the capillaries have only one thick cell: * ''[[Tunica intima]]'' (the thinnest layer): a single layer of simple squamous [[endothelium|endothelial cells]] glued by a [[polysaccharide]] intercellular matix, surrounded by a thin layer of subendothelial [[connective tissue]] interlaced with a number of circularly arranged elastic bands called the'' internal elastic lamina''. * ''[[Tunica media]]'' (the thickest layer): circularly arranged elastic fiber, connective tissue, polysaccharide substances, the second and third layer are separated by another thick elastic band called external elastic lamina. The tunica media may (especially in arteries) be rich in [[vascular smooth muscle]], which controls the caliber of the vessel. * ''[[Tunica adventitia]]'': entirely made of connective tissue. It also contains [[nerve]]s that supply the muscular layer, as well as nutrient capillaries ([[vasa vasorum]]) in the larger blood vessels. [[Capillary|Capillaries]] consist of little more than a layer of endothelium and occasional connective tissue. When blood vessels connect to form a region of diffuse vascular supply it is called an [[circulatory anastomosis|anastomosis]] (pl. anastomoses). Anastomoses provide critical alternative routes for blood to flow in case of blockages. Laid end to end, the blood vessels in an average human body will stretch approximately 62,000 miles (100,000 km)--2 times around the earth.{{fact|date=August 2007}} ==Types== There are various kinds of blood vessels: *[[Artery|Arteries]] **[[Aorta]] (the largest artery, carries blood out of the heart) **Branches of the aorta, such as the [[carotid artery]], the [[subclavian artery]], the [[celiac trunk]], the [[mesenteric artery|mesenteric arteries]], the [[renal artery]] and the [[iliac artery]]. *[[Arteriole]]s *[[Capillary|Capillaries]] (the smallest blood vessels) *[[Venule]]s *[[Vein]]s **Large collecting vessels, such as the [[subclavian vein]], the [[jugular vein]], the [[renal vein]] and the [[iliac vein]]. **[[Venae cavae]] (the 2 largest veins, carry blood into the heart) They are roughly grouped as ''arterial'' and ''venous'', determined by whether the blood in it is flowing ''away from'' (arterial) or ''toward'' (venous) the [[heart]]. The term "arterial blood" is nevertheless used to indicate blood high in [[oxygen]], although the [[pulmonary artery]] carries "venous blood" and blood flowing in the [[pulmonary vein]] is rich in oxygen. This is because they are carrying the blood to and from the lungs, respectively, to be oxygenated. ==Physiology== Blood vessels do not actively engage in the transport of blood (they have no appreciable [[peristalsis]]), but arteries - and veins to a degree - can regulate their inner diameter by contraction of the muscular layer. This changes the blood flow to downstream organs, and is determined by the [[autonomic nervous system]]. Vasodilation and vasoconstriction are also used antagonistically as methods of [[thermoregulation]].''' [[Oxygen]] (bound to [[hemoglobin]] in [[red blood cell]]s) is the most critical nutrient carried by the blood. In all arteries apart from the pulmonary artery, hemoglobin is highly saturated (95-100%) with oxygen. In all veins apart from the [[pulmonary vein]], the [[hemoglobin]] is desaturated at about 75%. (The values are reversed in the [[pulmonary]] circulation.) The [[blood pressure]] in blood vessels is traditionally expressed in [[torr|millimetres of mercury]] (1 mmHg = 133 [[Pascal (unit)|Pa]]). In the arterial system, this is usually around 120 mmHg [[systolic]] (high pressure wave due to contraction of the heart) and 80 mmHg [[diastolic]] (low pressure wave). In contrast, pressures in the venous system are constant and rarely exceed 10 mmHg. [[Vasoconstriction]] is the constriction of blood vessels (narrowing, becoming smaller in cross-sectional area) by contracting the [[vascular smooth muscle]] in the vessel walls. It is regulated by [[vasoconstrictor]]s (agents that cause vasoconstriction). These include [[paracrine]] factors (e.g. [[prostaglandin]]s), a number of [[hormone]]s (e.g. [[Antidiuretic hormone|vasopressin]] and [[angiotensin]]) and [[neurotransmitter]]s (e.g. [[epinephrine]]) from the nervous system. [[Vasodilation]] is a similar process mediated by antagonistically acting mediators. The most prominent vasodilator is [[nitric oxide]] (termed [[endothelium-derived relaxing factor]] for this reason). Permeability of the [[endothelium]] is pivotal in the release of nutrients to the tissue. It is also increased in [[inflammation]] in response to [[histamine]], [[prostaglandin]]s and [[interleukin]]s, which leads to most of the symptoms of inflammation (swelling, redness and warmth). ==Role in disease== Blood vessels play a role in virtually every medical condition. [[Cancer]], for example, cannot progress unless the tumor causes [[angiogenesis]] (formation of new blood vessels) to supply the malignant cells' metabolic demand. [[Atherosclerosis]], the formation of [[lipid]] lumps ([[atheroma]]s) in the blood vessel wall, is the prime cause of [[cardiovascular disease]], the main cause of death in the Western world. Blood vessel permeability is increased in [[inflammation]]. Damage, due to [[Physical trauma|trauma]] or spontaneously, may lead to [[haemorrhage]]. In contrast, occlusion of the blood vessel (e.g. by a ruptured atherosclerotic plaque, by an [[embolism|embolised]] [[blood clot]] or a foreign body) leads to downstream [[ischemia]] (insufficient blood supply) and [[necrosis]] (tissue breakdown). [[Vasculitis]] is [[inflammation]] of the vessel wall, due to [[autoimmune disease]] or [[infection]]. ==See also== *[[anastomosis]] *[[angioplasty]] *[[capacitance of blood vessels]] *[[vascular resistance]] *[[vascular surgery]] {{cardiovascular_system}} {{BloodVessels}} {{commons|Blood vessels}} [[Category:Cardiovascular system]] [[bs:Krvni sudovi]] [[cs:Céva]] [[da:Blodåre]] [[de:Blutgefäß]] [[dv:ލޭހޮޅި]] [[et:Veresoon]] [[es:Vaso sanguíneo]] [[fa:رگ]] [[fr:Vaisseau sanguin]] [[ko:혈관]] [[hr:Krvne žile]] [[id:Pembuluh darah]] [[is:Æð]] [[it:Vaso sanguigno]] [[ku:Xwînborî]] [[la:Vas sanguineum]] [[lv:Asinsvadi]] [[lt:Kraujagyslė]] [[mk:Крвни садови]] [[nl:Bloedvat]] [[ja:血管]] [[no:Blodåre]] [[nn:Blodåre]] [[nds:Bloodfatt]] [[pt:Vaso sanguíneo]] [[qu:Sirk'a]] [[ru:Кровеносный сосуд]] [[sq:Enët e gjakut]] [[simple:Blood vessel]] [[sk:Cieva (anatómia)]] [[sl:Žila]] [[sr:Крвни судови]] [[fi:Verisuoni]] [[sv:Blodkärl]] [[te:రక్తనాళాలు]] [[th:หลอดเลือด]] [[uk:Кровоносні судини]] [[fiu-vro:Suun]] [[yi:אדערן]] [[zh:血管]]