Show Summary Details
Page of

Physiology of body fluids 

Physiology of body fluids
Physiology of body fluids

Anthony Delaney

Page of

PRINTED FROM OXFORD MEDICINE ONLINE ( © Oxford University Press, 2022. All Rights Reserved. Under the terms of the licence agreement, an individual user may print out a PDF of a single chapter of a title in Oxford Medicine Online for personal use (for details see Privacy Policy and Legal Notice).

date: 16 May 2022

An understanding of the physiology of body fluids is essential when considering appropriate fluid resuscitation and fluid replacement therapy in critically-ill patients. In healthy humans, the body is composed of approximately 60% water, distributed between intracellular and an extracellular compartments. The extracellular compartment is divided into intravascular, interstitial and transcellular compartments. The movement of fluids between the intravascular and interstitial compartments, is classically described as being governed by Starling forces, leading to a small net efflux of fluid from the intravascular to the interstitial compartment. More recent evidence suggests that a model incorporating the effect of the endothelial glycoclayx layer, a web of glycoproteins and proteoglycans that are bound on the luminal side of the vascular endothelium, better explains the observed distribution of fluids. The movement of fluid to and from the intracellular compartment and the interstitial fluid compartment, is governed by the relative osmolarities of the two compartments. Body fluid status is governed by the difference between fluid inputs and outputs; fluid input is regulated by the thirst mechanism, with fluid outputs consisting of gastrointestinal, renal, and insensible losses. The regulation of intracellular fluid status is largely governed by the regulation of the interstitial fluid osmolarity, which is regulated by the secretion of antidiuretic hormone from the posterior pituitary gland. The regulation of extracellular volume status is regulated by a complex neuro-endocrine mechanism, designed to regulate sodium in the extracellular fluid.

Access to the complete content on Oxford Medicine Online requires a subscription or purchase. Public users are able to search the site and view the abstracts for each book and chapter without a subscription.

Please subscribe or login to access full text content.

If you have purchased a print title that contains an access token, please see the token for information about how to register your code.

For questions on access or troubleshooting, please check our FAQs, and if you can't find the answer there, please contact us.