3. Water and Electrolytes
– Water constitutes 50-55% of a woman's body weight and 55-60% of man's
weight. Water gives structure and form to the body, helps maintain body
temperature, and also creates the necessary environment for cell
metabolism and
– There are two compartments of body water, extracellular and intracellular
fluid. Extracellular fluid (ECF) is water found outside of cells. Making up
approximately 20% of total body weight, the ECF consists of blood plasma,
interstitial fluid surrounding the cells, secretory fluid, which is water in transit,
and dense tissue fluid, which is water located within dense connective tissue
such as cartilage and bone. Intracellular fluid (ICF) is the water inside the
cells. It makes up 35-40% of total body weight.
4. Sodium
– Sodium (Na) is the major cation (positively charged ion) in the extracellular fluid and
plays a variety of fundamental roles within the body.
– Sodium plays a large role in fluid balance, with different variations of sodium
determining the shift of water by osmosis from one area of the body to another. See
Cellular Control of Water Distribution
– Along with chloride and bicarbonate, sodium is important for the proper regulation
of the acid-base balance of the body.
– As an active transport mechanism in the form of Na, K –ATPase, sodium is essential
for the passage of metabolic materials through cell walls.
– Sodium, along with potassium, is responsible for balancing the response of nerves
to stimulation, travel of nerve impulses to muscles, and muscle contraction.
6. Absorption and Excretion of
potassium
– Dietary potassium is easily absorbed into the small intestine. Potassium
is lost through urinary excretion. Through the renal aldosterone
mechanism, potassium is lost in exchange for sodium. Approximately 160
mg of potassium is lost daily.