Page 54 - Anatomy and Physiology of Farm Animals, 8th Edition

Anatomy and Physiology of the Cell / 39

(A) isotonic with mammalian red blood
GLUCOSE MOLECULES cells and for this reason is called a
VetBooks.ir Distilled normal or physiologic saline solution.

water
Normal saline can be used to moisten
exposed tissues, such as open wounds,
without damaging the cells.
If the bathing fluid has a lower osmotic
Selectively pressure than the cells, it is said to be
Chamber B permeable Chamber A hypotonic, and water tends to cross the
membrane
membrane and enter the cells. In the case
of red blood cells in hypotonic plasma or
collected in to a volume of water, water will
enter the red blood cells, resulting in them
swelling and finally bursting, a condition
called hemolysis. If the bathing fluid is
(B) Volume Volume more concentrated than the cell cytoplasm,
decreased Increased
then cells will lose water to the hypertonic
solution. If red blood cells are in hypertonic
plasma, they become wrinkled as they lose
water, a process called crenation. In rela­
Chamber B Osmotic Chamber A tion to mammalian cells, a solution less
force concentrated than 0.9% sodium chloride is
said to be hypotonic; one more concen­
trated than 0.9% sodium chloride is said to
be hypertonic; and of course a 0.9% sodium
chloride solution is isotonic.
The osmotic pressure of a solution is
Figure 2-13. Osmosis and osmotic pressure.
A membrane impermeable to solute particles determined by the number of solute parti­
prevents their diffusion from chamber A into cles: the more solute particles in a volume
chamber B. Distilled water from chamber B of fluid, the greater the osmotic pressure.
migrates into chamber A until the difference in The number of particles is determined by
the height of the water columns equals the osmotic the molar concentration of the solution
pressure of the solution in chamber A. and by the number of ions formed if the
solute is an electrolyte. For example, glucose
is not an electrolyte, having one particle
to the osmotic force (Fig. 2‐13). The units of per molecule, but sodium chloride is an
osmotic pressure may be given in centime­ electrolyte, giving two particles (Na and
+
ters of water (height of water column), or Cl ) per molecule when placed in solution.
−
converted to millimeters of mercury (mmHg; A 1‐molar solution of sodium chloride has
height of a column of mercury creating an twice the osmotic pressure of a 1‐molar
equivalent amount of hydrostatic pressure). solution of glucose, because the sodium
Osmotic pressure is an important chloride solution has twice the number of
mechanism in maintaining cellular volume particles in solution.
by determining whether water will enter or These concepts of osmosis and osmotic
leave cells. If the concentration of solutions pressure become important when intrave­
on each side of a membrane is the same, as nous fluids are administered to animals for
seen with cells in blood, the extracellular or problems such as dehydration, anorexia,
bathing fluid is said to be isotonic (isosmotic) milk fever, and diarrhea. Furthermore, they
in relation to the cells. This means that the are important principles in normal func­
osmotic pressure is the same on both sides tions of animals, such as the flow of blood
of the membrane. A 0.9% solution of and lymph, the excretion of wastes in the
sodium chloride is considered to be urine by the kidneys, and the digestion