Extracellular space

Extracellular spacerefers to the part of amulticellular organismoutside thecells,usually taken to be outside theplasma membranes,and occupied by fluid. This is distinguished fromintracellular space,which is inside the cells.

The composition of the extracellular space includesmetabolites,ions,proteins,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.Hormonesalso act by travelling the extracellular space towardscell receptors.

Incell biology,molecular biologyand related fields, the wordextracellular(or sometimesextracellular space) means "outside thecell".This space is usually taken to be outside theplasma membranes,and occupied by fluid (seeextracellular matrix). The term is used in contrast tointracellular(inside the cell).

According to theGene Ontology,the extracellular space is a cellular component defined as: "That part of a multicellular organism outside the cells proper, usually taken to be outside the plasma membranes, and occupied by fluid. For multicellular organisms, the extracellular space refers to everything outside a cell, but still within the organism (excluding the extracellular matrix). Gene products from a multi-cellular organism that are secreted from a cell into the interstitial fluid or blood can therefore be annotated to this term".

The composition of the extracellular space includesmetabolites,ions,variousproteinsand non-protein substances (e.g. DNA, RNA, lipids, microbial products etc.), and particles such asextracellular vesiclesthat might affect cellular function. For example,hormones,growth factors,cytokinesandchemokinesact by travelling the extracellular space towardsbiochemical receptorson cells. Other proteins that are active outside the cell are variousenzymes,including digestive enzymes (Trypsin,Pepsin), extracellular proteinases (Matrix metalloproteinases,ADAMTSs,Cathepsins) and antioxidant enzymes (extracellularsuperoxide dismutase). Often, proteins present in the extracellular space are stored outside the cells by attaching to various extracellular matrix components (Collagens,Proteoglycans,etc.).In addition, extracellular matrix proteolytic products are also present in the extracellular space, especially in tissues undergoing remodelling[2].