Page 44 - Anatomy and Physiology of Farm Animals, 8th Edition

Anatomy and Physiology of the Cell / 29

translated for protein synthesis within the of measurements of body fluid electrolyte
and ion concentrations are often expressed
cytoplasm of the cell.
VetBooks.ir part of the diet of most animals, the amount as milliequivalents per liter (mEq/L).
Even though carbohydrates are a major
Another way of expressing measurements
of carbohydrates in animal’s bodies is is in mg%, or milligrams per 100 milliliters
relatively small. Carbohydrates make up (mg/100 mL). Some constituents are also
less than 1% of most cells. reported as either millimoles per liter
(mmol/L) or as milligrams per deciliter
(mg/dL); a deciliter is 100 mL, or a tenth of
Inorganic Substances a liter. A liter is 1000 mL, or 1.06 quarts.

Of the atoms or elements found in proto­ Acids, Bases, and pH
plasm, more than 99% are hydrogen, car­
bon, oxygen, and nitrogen contained in the An acid is a compound that is capable of
organic compounds described earlier. Bone ionizing and releasing a hydrogen ion. The
contains about 65% inorganic material by pH of a solution is a measure of the concen­
volume. Most of this mineral material is in tration of H . However, pH is reported as
+
the form of hydroxyapatite crystals with the negative of the logarithm to the base
a molecular formula Ca (PO ) (OH) . In 10 of the H concentration in moles, so the
+
10
4 6
2
addition, sodium, magnesium, and iron may greater the H concentration, the more
+
be incorporated in the mineral structure. negative, or lower, the pH. Concentrations
Protoplasm also has inorganic compounds of H in normal body fluids are much lower
+
containing iodine, iron, phosphorus, calcium, than other electrolytes. A typical H con­
+
chlorine, potassium, sulfur, sodium, magne­ centration in plasma is 4 × 10 moles per
−9
sium, copper, manganese, zinc, cobalt, liter, or 4 nanomoles per liter, equivalent to
chromium, selenium, molybdenum, fluo­ a pH of 7.45. A nanomole is one‐millionth
rine, silicon, tin, and vanadium. Of the 24 of a millimole.
elements found in the body cells, 20 repre­ A base is a compound that is capable of
sent less than 1% of the total amount of reducing the concentration of hydrogen ions
elements in living tissue. in a solution by combining with them. When
An electrolyte is any molecular substance bases are added to solutions, the H concen­
+
that in solution dissociates into its electri­ tration is reduced, so the pH rises. Chemical
cally charged components, called ions. For buffer solutions contain both acids and
example, this occurs when sodium chloride bases and therefore are capable of either
in solution dissociates into Na and Cl . The releasing or combining with H . This dual
−
+
+
solution can then carry an electrical charge ability tends to provide a relatively stable pH.
and current. All body fluids, intracellular and extra­
The major ions found within cells in order cellular, contain mixtures of several chemi­
of abundance, expressed in milliequiva­ cal buffers. These buffers act simultaneously
lents per liter of fluid, are: potassium (K ) to maintain a relatively stable pH within
+
140 mEq/L; phosphate (HPO ), 75 mEq/L; their respective fluids. This stability is crit­
2−
4
magnesium (Mg ), 60 mEq/L; sodium (Na ) ical for normal metabolic processes and
+
2+
10 mEq/L; bicarbonate (HCO ) 10 mEq/L; enzymatic reactions.
−
3
and chloride (Cl ) 4 mEq/L.
−
A milliequivalent is one‐thousandth of
an equivalent. An equivalent weight is the Microscopic Study of the Cell
weight in grams that will displace or react
with 1 gram atomic weight of hydrogen ion Cells range in diameter from about 10 to
(H = 1.008 g). 100 μm (micrometers). Cells that are actively
+
The practical importance of this con­ multiplying range from about 20 to 30 μm
cept is that laboratory reports and records in diameter. Table 2‐1 lists the relationships