Chapter 18 - Water, Electrolyte, and Acid-Base Balance
To be in balance, the quantities of fluids and electrolytes leaving the body should be equal
to the amounts taken in.
Anything that alters the concentrations of electrolytes will also alter the concentration
and vice versa.
Distribution of Body Fluids
Fluids occur in compartments in the body, and movement of water and electrolytes
between compartments is regulated.
Fluid Compartments (p. 502; Fig. 18.1)
The average adult female is 52% water by weight, while a male is 63% water, the
difference due to the female's additional adipose tissue.
The intracellular fluid compartment includes all the water and electrolytes
The extracellular fluid compartment includes all water and electrolytes outside
of cells (interstitial fluid, plasma, and lymph).
Transcellular fluid includes the cerebrospinal fluid of the central nervous system,
fluids within the eyeball, synovial fluid of the joints, serous fluid within body
cavities, and exocrine gland secretions.
Body Fluid Composition (p. 502; Fig. 18.2)
Extracellular fluids have high concentrations of sodium, chloride, and
bicarbonate ions, and lesser amounts of potassium, calcium, magnesium,
phosphate, and sulfate ions.
Intracellular fluid has high concentrations of potassium, phosphate, and
magnesium ions, and lesser amounts of sodium, chloride, and bicarbonate ions.
Movement of Fluid between Compartments (p. 503; Fig. 18.3)
Hydrostatic pressure and osmotic pressure regulate the movement of water and
electrolytes from one compartment to another.