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.