Description
a. Cell membranes separate the interstitial fluid from
the intravascular fluid.
b. Cell membranes are selectively permeable; that is,
the cell membrane and the capillary wall will
allow water and some solutes free passage through
them.
c. Several forces affect the movement of water and
solutes through the walls of cells and capillaries.
d. The greater the number of particles within the cell,
the more pressure exists to force the water through
the cell membrane.
e. If the body loses more electrolytes than fluids, as
can happen in diarrhea, then the extracellular fluid
will contain fewer electrolytes or less solute than
the intracellular fluid.
f. Fluids and electrolytes must be kept in balance for
health; when they remain out of balance, death can
occur.
Isotonic solutions
a. When the solutions on both sides of a selectively
permeable membrane have established equilibrium
or are equal in concentration, they are isotonic.
b. An example of an isotonic solution is 0.9% sodium
chloride, which is referred to as isotonic saline
solution or normal saline solution.
c. Isotonic solutions are isotonic to human cells, and
thus very little osmosis occurs; isotonic solutions
have the same osmolality as body fluids.
d. Other solutions that are isotonic are 5% dextrose in
water, 5% dextrose in 0.225% saline, and Ringer's
lactate solution.
Hypotonic solutions
a. When a solution contains a lower concentration of
salt or solute than another more concentrated
solution, it is considered hypotonic.
b. A hypotonic solution has less salt or more water
than an isotonic solution; these solutions have
lower osmolality than body fluids.
c. 0.45% sodium chloride, 0.225% sodium chloride,
and 0.33% sodium chloride are examples of
hypotonic solutions.
d. Hypotonic solutions are hypotonic to the cells;
therefore, osmosis would continue in an attempt to
bring about balance or equality.
Hypertonic solutions
a. A solution that has a higher concentration of
solutes than another less concentrated solution is
hypertonic; these solutions have a higher
osmolality than body fluids.
b. Hypertonic solutions include 3% sodium chloride,
5% sodium chloride, 10% dextrose in water, 5%
dextrose in 0.9% sodium chloride, 5% dextrose in
0.45% sodium chloride, and 5% dextrose in
Ringer's lactate solution.
Osmotic pressure
a. The amount of osmotic pressure is determined by
the concentration of solutes in solution.
b. When the solutions on each side of a selectively
permeable membrane are equal in concentration,
they are isotonic.
c. A hypotonic solution has less solute than an
isotonic solution, whereas a hypertonic solution
contains more solute.
d. A solvent will move from the less concentrated
solute side to the more concentrated solute side to
equalize concentration.
Active transport
a. If an ion is to move through a membrane from an
area of lower concentration to an area of higher
concentration, an active transport system is
necessary.
b. An active transport system moves molecules or
ions against concentration and osmotic pressure.
c. Metabolic processes in the cell supply the energy
for active transport.
d. Substances that are transported actively through
the cell membrane include ions of sodium,
potassium, calcium, iron, and hydrogen, some of
the sugars, and the amino acids.
Categories:
CONCEPTS OF FLUID AND ELECTROLYTE BALANCE