Extracellular 974030 222916745 2008-07-01T18:57:27Z Delldot 476500 ce In [[cell biology]], [[molecular biology]] and related fields, the word '''extracellular''' (or sometimes '''extracellular space''') means "outside the [[cell (biology)|cell]]". This space is usually taken to be outside the [[plasma membrane]]s, and occupied by fluid. The term is used in contrast to [[intracellular]] (inside the cell). The composition of the extracellular space includes [[metabolites]], [[ion]]s, [[protein]]s, and many other substances that might affect cellular function. For example, [[neurotransmitters]] "jump" from cell to cell to facilitate the transmission of an electric current in the nervous system. [[Hormone]]s also act by travelling the extracellular space towards [[biochemical receptor]]s on cells. Other proteins that are active outside the cell are the digestive [[enzymes]]. The term 'extracellular' is often used in reference to the [[extracellular fluid]] (ECF) which composes about 15 [[litre]]s of the average human body. The [[cell membrane]] (and, in plants and fungi, the [[cell wall]]) is the barrier between the two, and chemical composition of intra- and extracellular [[wiktionary:milieu|milieu]] can be radically different. In most organisms, for example, a [[Na+/K+-ATPase|Na<sup>+</sup>/K<sup>+</sup>-ATPase]] pump maintains a high [[concentration]] of [[sodium]] [[ion]]s outside cells while keeping that of [[potassium]] low, leading to chemical excitability. Many cold-tolerant plants force water into the extracellular space when the temperature drops below 0&nbsp;degrees Celsius, so that when it freezes, it does not [[lysis|lyse]] the plants' cells. <ref>Taiz, Lincoln. Plant Physiology, 4th ed. 2006. Sinaeur Associates, Inc.</ref> Two compartments comprise the extracellular space: the [[vascular space]] and the [[interstitial space (biology)|interstitial space]].<ref name="Fleischhauer95"> {{ cite journal |author=Fleischhauer J, Lehmann L, Kléber AG |title=Electrical resistances of interstitial and microvascular space as determinants of the extracellular electrical field and velocity of propagation in ventricular myocardium |journal=Circulation |volume=92 |issue=3 |pages=587–94 |year=1995 |month=August |pmid=7634473 |doi= |url=http://www.circ.ahajournals.org/cgi/content/full/92/3/587 }} </ref> ==References== {{reflist}} {{Cell-biology-stub}} [[Category:Cell anatomy]] [[cs:Mezibuněčný prostor]] [[de:Extrazellularraum]]