What is Capillary?
[[File:Illu capillary.jpg |thumb|300px|Blood flows from the heart to [[artery|arteries]], which narrow into [[arteriole]]s, and then narrow further still into capillaries. After the tissue has been [[perfusion|perfused]], capillaries widen to become venules and then widen more to become veins, which return blood to the heart.]] A '''capillary''' is a [[blood vessel]]. It does not have the muscular/elastic [[tissue (biological)|tissue]] of other blood vessels. It has a single [[cell wall|celled wall]] to help substances be transported through [[organism]]s. Capillaries are small, and smaller than any other [[blood vessel]]s. They are about 5-10 [[micrometre|μms]] big, connect [[arteries]] and [[venule]]s, and enable the moving of [[water]], [[oxygen]], [[carbon dioxide]], as well as many other [[nutrient|nutrients]] and [[waste]] [[chemical|chemicals]] between [[blood]] and surrounding [[tissue (biology)|tissues]].<ref>{{cite book | last = Maton | first = Anthea | authorlink = | author2 = Jean Hopkins, Charles William McLaughlin, Susan Johnson, Maryanna Quon Warner, David LaHart, Jill D. Wright | title = Human Biology and Health | publisher = Prentice Hall | date = 1993 | location = Englewood Cliffs, New Jersey. | pages = | url = https://archive.org/details/humanbiologyheal00scho | isbn = 0-13-981176-1}}</ref> == Anatomy == Blood moves from the [[heart]] to [[arteries]], which branch and narrow into [[arterioles|smaller arteries]], and then branch more into capillaries. At the capillaries, gases, nutrients, and fluids, are exchanged, with the exact nature and direction of the exchange depending on the location of the capillary bed. For instance, blood traveling through capillaries of the systemic circuit releases oxygen and absorbs carbon dioxide, while blood traveling through the pulmonary capillaries absorbs oxygen and releases carbon dioxide. After this exchange, capillaries join and widen to become small veins and then widen more to become veins, which return blood to the heart.<ref>