Summary
Body water is divided into intracellular and extracellular fluid, with distinct ion compositions.
In depth
Total body water is about 60 percent of weight: two-thirds intracellular, one-third extracellular (plasma and interstitial). Intracellular fluid is rich in K+, extracellular in Na+ and Cl-. Oncotic pressure from albumin retains plasma.
Water moves between compartments by osmosis and hydrostatic pressure. Starling forces govern capillary exchange.
Remember: oedema is excess interstitial fluid.
In a 70 kg person, total body water is about 42 litres: intracellular fluid about 28 litres, interstitial fluid about 11 litres and plasma about 3 litres. Water moves between compartments by osmosis, with Starling forces for capillaries. Ion composition differs: intracellular is high in K+ and proteins, extracellular in Na+ and Cl-. Women and older people have less water because of higher fat and lower muscle.
Dehydration, oedema and shifts in electrolytes disturb compartments; intravenous fluids are chosen accordingly: isotonic saline stays outside cells and expands extracellular volume, 5 percent dextrose becomes free water, and plasma expanders such as albumin remain in the vessels. Dilution techniques (tracers such as deuterium or inulin) measure compartments.
Example: in burns, plasma leaks into tissues causing large fluid losses and shock.
Frequently asked questions
What is Fluid Compartments?
Body water is divided into intracellular and extracellular fluid, with distinct ion compositions.
Which area of biology covers Fluid Compartments, and how advanced is it?
Fluid Compartments is one of the 51 topics in Human Physiology. It is rated Advanced, so it suits learners who want specialist depth. Related topics in this area include Blood Vessels, Breathing Mechanism, Circulatory System.
Can you give an example of Fluid Compartments?
Low albumin causes oedema.
What should I learn before Fluid Compartments?
Work through the Beginner topics in Human Physiology first, such as Homeostasis, Tissues and Organs, Skeletal System, then return to Fluid Compartments. Advanced topics assume the Intermediate vocabulary.
What topics are related to Fluid Compartments?
The closest topics to Fluid Compartments are Blood Vessels, Breathing Mechanism, Circulatory System, Gas Exchange in Alveoli. Comparing them side by side is a good way to see how the ideas connect.
How can I check that I understand Fluid Compartments?
Read the summary and the in-depth section, then use the quick check on the interactive lesson for Fluid Compartments. To practise the whole of Human Physiology, use the Human Physiology quiz.
How is Fluid Compartments different from Blood Vessels?
Fluid Compartments: Body water is divided into intracellular and extracellular fluid, with distinct ion compositions. Blood Vessels: Arteries carry blood away from the heart, veins return it and capillaries exchange materials. Read both side by side and note what each one explains.
How should I study Fluid Compartments step by step?
First, read the summary and write the definition in your own words. Second, read the in-depth section and note any example. Third, compare it with Blood Vessels and explain the difference aloud. Finally, take the Human Physiology quiz and come back to this page for any question you miss.