Basic Physiology, Body Fluids, Membrane Transport, Nerve and Muscle Function

Intracellular Fluids

Intracellular Fluids n (ICF) include all the water and electrolytes enclosed by the cell membranes.

Intracellular fluid is the solvent in which all the reactions occurring within the cell take place. As such it is extemely important that the composition of this compartment do not vary to a great extent.

Extracellular Fluids

The Extracellular fluid (ECF) includes all fluids outside the cells. This fluid can be divided into three fluid departments:

1.	Interstitial (in the tissue spaces) fluid
2.	Blood Plasma and lymph
3.	Specialised compartments called Transcellular Fluid e.g. cerebrospinal fluid, synovial fluid, humors of the eye, pleural, peritoneal and percardial fluid and glandular fluids

The extracellular fluid surrounds all the cells in the body and is in equilibrium with the intracellular fluid. Thus itcomposition must remain fairly constant even though substances are passing into and out of the cells.

The interstitial fluid, though called a fluid, is in a reality a gel-like composition made up of

water,
proteoglycan molecules (high molecular weight mucopolysacharides) and
collagen.

Advantages of gel-matrix in contrast to just a fluid:

1.	Proteoglycan molecules keep cells apart - easier diffusion of substances;
2.	Prevents fluid from pooling to the lower extremities;
3.	Hinders the spread of bacteria and other micro-organisms.