Chapter 25
Body Fluids and Acid-Base Balance
By Boundless
Fluid can enter the body as preformed water, ingested food and drink, and to a lesser extent, as metabolic water.
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Fluid can leave the body in several ways: urination, exretion (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.
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Dehydration is the excessive loss of body fluid.
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A significant percentage of the human body is water, which includes intracellular and extracellular fluids.
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The major body fluid compartments include: intracellular fluid and extracellular fluid (plasma, interstitial fluid, and trancellular fluid).
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The composition of tissue fluid depends upon the exchanges between the cells in the biological tissue and the blood.
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Movement of fluid among compartments depends on several variables described by Starling's equation.
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Electrolytes play a vital role in maintaining homeostasis within the body.
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Sodium is an important cation distributed primarily outside the cell.
Potassium is mainly an intracellular ion.
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Calcium is a key electrolyte: 99% is deposited in bone and the remainder is associated with hormone release and cell signalling.
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Anions chloride, bicarbonate, and phosphate have important roles in maintaining balances and neutrality of vital mechanisms in the body.
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Acids dissociate into H+ and lower pH, while bases dissociate into OH- and raise pH; buffers can absorb these excess ions to maintain pH.
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Chemical buffers such as bicarbonate and ammonia help keep blood pH in the narrow range compatible with life.
![Thumbnail](../../../../../figures.boundless-cdn.com/8932/raw/expiration-diagram.jpg)
Acid-base imbalances in blood pH can be altered by changes in breathing to expel more CO2, which will raise pH back to normal.
The kidneys help maintain acid-base balance by excreting hydrogen ions into the urine and reabsorbing bicarbonate from the urine.