Fuid Compartments

02/07/2009 16:38

Fluids and Electrolytes:

Fluid compartments:

1.        ICF – Intracellular Fluid

           About 2/3 by volume.   This is the fluid within the cells.  It provides nutrients for metabolism because it is high in Potassium, Phosphate, and protein; and moderate levels of Magnesium and Sulfate.  It also assists in cellular metabolism.

2.       ECF – Extracellular fluid

           ECF is comprised by three major components:

a.        Intravascular – Plasma (the fluid portion of blood)

b.      Interstitial – Fluid in and around the tissues

c.       Transcellular – Over and across the cells found in cerebrospinal fluid, eye humors, synovial fluid, serous fluid, and gastrointestinal secretions.

Regulations of Fluid in Compartments:

1.        Osmosis – Movement of water through a selectively permeable membrane from an area of low solute concentration to a higher concentration until equilibrium occurs.

2.       Diffusion – Movement of solutes from an area of a higher concentration to an area of lower concentration in a solution and/or across a permeable membrane.

3.       Active Transport – Allows molecules to move against concentration and osmotic pressure to areas of higher concentration


Osmolality – the concentration of body fluids which reflects hydration status.  It is measured by urine and serum.

Normal serum value: 280- 300 mOsm/kg   *<240 and >320 is critically abnormal

Serum Osml/L =(serum Na x 2) + BUN/3 + Glucose/18