I.                    Water comprises up to 70% of the weight in a human. People who are thin, low-fat, and young tend to have more water.

II.                 where its located (compartments):

a.       Intracellular (65% of total body water). This would be in the cells themselves – most of the water in cells would be in muscle cells. Adipose cells hold little water.

b.      Extracellular (35% of total body water) – all the water outside cells. 

                                                               i.      This would be in the areas around the cell (interstitial 2/3 of the 35%) or

                                                             ii.      in the blood vessels (1/3 of the 35%)… the water in the blood.

1.      Important fact: 7% of body weight is blood volume (1/3 of 35% of a max 70% weight). 

III.               The intracellular compartment contains more Potassium while the extracellular compartment contains more Sodium.