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Extracellular fluid facts for kids

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Extracellular fluid is body fluid that exists outside cells. It makes up about one-third (1/3) of all body water.


Cellular Fluid Content
Extracellular fluid content in humans

The main component of the extracellular fluid is the interstitial 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 interstitial fluid and the plasma make up about 97% of the ECF, and a small percentage of this is lymph. The remaining small percentage of ECF includes the transcellular fluid. These constituents are often called compartments. The transcellular fluid includes the aqueous humour in the eye, the synovial fluid in the joints, the cerebrospinal fluid in the brain and spinal cord, the serous fluid in the serous membranes lining body cavities and in the saliva and other gut fluids (gastric juice, pancreatic juice and other intestinal secretions), as well as the perilymph and endolymph in the inner ear.

The volume of extracellular fluid in a young adult male of 70kg, is 20% of body weight – about fourteen litres. Eleven litres is interstitial fluid and the remaining three litres is plasma.


Cell membrane detailed diagram en
Cell membrane details between extracellular and intracellular fluid

The extracellular fluid provides the medium for the exchange of substances between the ECF and the cells, and this can take place through dissolving, mixing and transporting in the fluid medium. Substances in the ECF include dissolved gases, nutrients, and electrolytes, all needed to maintain life. The ECF also contains materials secreted from cells in soluble form, but which quickly coalesces into fibres (e.g. collagen, reticular, and elastic fibres) or precipitates out into a solid or semisolid form (e.g. proteoglycans which form the bulk of cartilage, and the components of bone). These and many other substances occur, especially in association with various proteoglycans to form the extracellular matrix or the "filler" substance between the cells throughout the body. These substances occur in the extracellular space, and are therefore all bathed or soaked in ECF, without being part of the ECF.

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