Homeostasis 2, Fluid Balance 

Cells, tissues and fluids
In an average adult body there is approximately 42 litres of water, comprising around 60% of body weight. Most water, normally around 28 litres, is found inside the cells which comprise the body. Although in reality this water is located in billions of individual cells it is collectively referred to as the intracellular compartment. The remaining 14 litres of the fluid in the body is located outside the cells so is termed extracellular fluid. Total blood volume in an adult is usually about 5 litres. This is located in the heart and various blood vessels, a space collectively referred to as the vascular compartment. However, only 3 litres of the blood volume is made up of water, the other 2 litres are blood cells. This leaves approximately 11 litres of extracellular fluid which is located in the tissues. This tissue or interstitial fluid is located in the interstitial compartment which in reality is in all of the tissue spaces of the body.