Editing Extracellular fluid (section)

== Components ==
The main component of the extracellular fluid (ECF) is the interstitial fluid, or tissue fluid, which surrounds the cells in the body. The other major component of the ECF is the intravascular fluid of the [[circulatory system]] called [[blood plasma]].  The remaining small percentage of ECF includes the transcellular fluid. These constituents are often called "[[fluid compartments]]". The volume of extracellular fluid in a young adult male of 70&nbsp;kg, is 20% of body weight – about fourteen liters.

===Interstitial fluid===
{{See also|Fluid compartments#Interstitial compartment|Lymph#Development}}

Interstitial fluid is essentially comparable to [[blood plasma|plasma]]. The interstitial fluid and plasma make up about 97% of the ECF, and a small percentage of this is [[lymph]].

Interstitial fluid is the body fluid between blood vessels and cells,<ref name="Wiig Swartz 2012 pp. 1005–1060">{{cite journal | last1=Wiig | first1=Helge | last2=Swartz | first2=Melody A. | s2cid=11394172 | title=Interstitial Fluid and Lymph Formation and Transport: Physiological Regulation and Roles in Inflammation and Cancer | journal=Physiological Reviews | publisher=American Physiological Society | volume=92 | issue=3 | year=2012 | issn=0031-9333 | pmid=22811424 | doi=10.1152/physrev.00037.2011 | pages=1005–1060}}</ref> containing nutrients from [[Capillary|capillaries]] by diffusion and holding waste products discharged by cells due to [[metabolism]].<ref>{{Cite web |date=2011-02-02 |title=Definition of interstitial fluid |url=https://www.cancer.gov/publications/dictionaries/cancer-terms/def/interstitial-fluid |access-date=2022-03-08 |website=www.cancer.gov |language=en}}</ref><ref name="Diabetes Community, Support, Education, Recipes & Resources 2019">{{cite web | title=Interstitial Fluid – What is the Role of Interstitial Fluid | website=Diabetes Community, Support, Education, Recipes & Resources | date=2019-07-22 | url=https://www.diabetes.co.uk/body/interstitial-fluid.html | access-date=2019-07-22}}</ref> 11 liters of the ECF are interstitial fluid and the remaining three liters are plasma.<ref name="Hall"/> Plasma and interstitial fluid are very similar because water, ions, and small solutes are continuously exchanged between them across the walls of capillaries, through pores and [[Intercellular cleft#Capillary intercellular clefts|capillary clefts]].

Interstitial fluid consists of a water solvent containing sugars, salts, fatty acids, amino acids, coenzymes, hormones, neurotransmitters, white blood cells and cell waste-products. This solution accounts for 26% of the water in the human body. The composition of interstitial fluid depends upon the exchanges between the cells in the biological tissue and the blood.<ref name=":0">Widmaier, Eric P., Hershel Raff, Kevin T. Strang, and Arthur J. Vander. "Body Fluid Compartments." ''Vander's Human Physiology: The Mechanisms of Body Function''. 14th ed. New York: McGraw-Hill, 2016. 400–401. Print.</ref> This means that tissue fluid has a different composition in different tissues and in different areas of the body.

The plasma that filters through the blood capillaries into the interstitial fluid does not contain red blood cells or platelets as they are too large to pass through but can contain some white blood cells to help the immune system.

Once the extracellular fluid collects into small vessels ([[Lymph capillary|lymph capillaries]]) it is considered to be lymph, and the vessels that carry it back to the blood are called the lymphatic vessels. The lymphatic system returns protein and excess interstitial fluid to the circulation.

The ionic composition of the interstitial fluid and blood plasma vary due to the [[Gibbs–Donnan effect]]. This causes a slight difference in the concentration of cations and anions between the two fluid compartments.

===Transcellular fluid===
{{See also|Fluid compartments#Transcellular compartment}}

Transcellular fluid is formed from the [[Cell physiology#Physiological processes|transport activities of cells]], and is the smallest component of extracellular fluid. These fluids are contained within [[epithelial]] lined spaces. Examples of this fluid are [[cerebrospinal fluid]], [[aqueous humor]] in the eye, [[serous fluid]] in the [[serous membranes]] lining [[Body cavity|body cavities]], [[perilymph]] and [[endolymph]] in the inner ear, and [[synovial fluid|joint fluid]].<ref name=":1" /><ref>{{Cite book|title=Physiology | edition = 5th |last=Constanzo|first=Linda S. | name-list-style = vanc |publisher=Elsevier Saunders|year=2014|isbn=9781455708475|pages=264}}</ref> Due to the varying locations of transcellular fluid, the composition changes dramatically. Some of the electrolytes present in the transcellular fluid are [[sodium]] ions, [[chloride ion]]s, and [[bicarbonate]] ions.