The extracellular fluid pertains to all body fluid outside the cell(s). It makes up about 26% of the total body water composition in humans. It is composed of blood plasma, interstitial fluid, lymph and transcellular fluid. The interstitial fluid and the blood plasma are the major components of the extracellular fluid. The transcellular fluid is the smallest component of the extracellular fluid.
The transcellular fluid is the fluid that fills up the spaces of chambers that are created or formed from the linings of epithelial cells. It is largely made up of water. However, other components (e.g. electrolytes) vary depending on the location. Thus, the function of transcellular fluid also varies. For instance, the synovial fluid serves as a lubricating fluid whereas urine, as the fluid containing the by-products of metabolism processed by the kidneys, aids in maintaining homeostasis when it is eliminated through urination.
The transcellular fluid is exemplified by the following:
- cerebrospinal fluid
- synovial fluid (joint fluid)
- aqueous humour (ocular fluid)
- serous fluid in serous membranes of body cavities
- gastrointestinal fluid (e.g. gastric juice and other intestinal secretions)
- bladder fluids (urine)
- perilymph and endolymph in the inner ear
- pericardial fluid
- intrapleural fluid
Word origin: Latin trāns ("across", "beyond", "through") + cellulāris, cellul(a) ("live cell")