Concepts of Fluid and Electrolyte Balance
(Chapter 13)
Filtration: the movement of fluid (water) through a cell or blood vessel membrane
because of hydrostatic pressure (water pressure) differences on both sides of the
membrane.
oBlood pressure
Diffusion: the movement of particles (solute) across a permeable membrane from an
area of higher particle concentration to an area of lower particle concentration (down a
concentration difference or “gradient”.
oTransport of most electrolytes and other particles through a cell membrane
Osmosis: movement of water only through a semipermeable to achieve an equilibrium
of osmolarity.
Age, gender, and fat affect the amount and distribution pf body fluids.
Fluid loss occurs through several routes.
oKidneys, skin, lungs, intestinal tract
Kidneys: the major regulator of water and sodium balance; maintain blood and
perfusion pressure to all tissues/organs.
When the kidneys sense a low parameter, they secrete renin.
Renin-Angiotensin II: a pathway that is greatly stimulated with shock, or when a stress
response is stimulated.
Sodium: 135-145 mmol/L
oWater always follows
Potassium: 3.5-5.0 mEq/L
oMajor cation of intracellular fluid (ICF).
Calcium: 2-2.6 mmol/L
oAbsorption requires the active form of vitamin D.
