Fluid can enter the body as preformed water, ingested food and drink, and, to a lesser extent, as metabolic water.
Fluid can leave the body in three ways: urination, excretion (feces), and perspiration (sweating).
Urea, a nitrogenous waste material, is the end product excreted in urine when ammonia is metabolized by animals, such as mammals.
Dehydration is the excessive loss of body fluid.
A significant percentage of the human body is water, which includes intracellular and extracellular fluids.
The major body-fluid compartments includ: intracellular fluid and extracellular fluid (plasma, interstitial fluid, and transcellular fluid).
The composition of tissue fluid depends upon the exchanges between the cells in the biological tissue and the blood.
How fluid moves through compartments depends on several variables described by Starling's equation.
Electrolytes play a vital role in maintaining homeostasis within the body.
Sodium is an important cation that is distributed primarily outside the cell.
Potassium is mainly an intracellular ion.
Calcium is a key electrolyte: 99% is deposited in the bones and the remainder is associated with hormone release and cell signaling.
The anions chloride, bicarbonate, and phosphate have important roles in maintaining the balances and neutrality of vital body mechanisms.
Acids dissociate into H+ and lower pH, while bases dissociate into OH- and raise pH; buffers can absorb these excess ions to maintain pH.
Chemical buffers, such as bicarbonate and ammonia, help keep the blood's pH in the narrow range that is compatible with life.
Acid–base imbalances in the blood's pH can be altered by changes in breathing to expel more CO2 and raise pH back to normal.
The kidneys help maintain the acid–base balance by excreting hydrogen ions into the urine and reabsorbing bicarbonate from the urine.