Page 453 - Anatomy and Physiology of Farm Animals, 8th Edition

438 / Anatomy and Physiology of Farm Animals

in the extracellular fluid, and hydrogen the buffering capacities of the extracellular
When an acid‐base imbalance arises and
ions from the extracellular fluid must
VetBooks.ir enter cells to be buffered by the intracel- and intracellular chemical buffers are over-
whelmed, the body systems primarily
lular proteins (Fig. 23‐13). Hemoglobin
proteins in erythrocytes are a major con- responsible for acid‐base balance (respira-
tributor to the total buffering capacity of tory and urinary) should respond. This
whole blood. response may lead to a state of compensa-
Acids and bases are produced by normal tion, so that the acid‐base imbalance is less
cellular metabolism and are constantly severe than if the compensation (or
being added to the ECF (Fig. 23‐13). Acids response) had not occurred. For example,
and bases are also added to the ECF by gas- chronic lung diseases may result in an
trointestinal absorption. Normally, these accumulation of carbon dioxide and a
additions are balanced by the actions of the respiratory acidosis. The kidneys com-
urinary and respiratory systems so that pensate for the respiratory acidosis by
extracellular fluid pH (Fig. 23‐13) and the producing a more acidic urine and
status of body buffer systems, including retaining base (bicarbonate). An increase
intracellular proteins, remain stable. in blood bicarbonate concentration is an
However, the ability of these mechanisms to indicator of renal compensation for the
maintain a normal pH can be overwhelmed primary respiratory acidosis.
during metabolic disturbances or after the Because of its importance as the major
absorption of large amounts of acids or extracellular buffer system and because the
bases from the gastrointestinal tract. components of the system can be readily
Ruminal or lactic acidosis is seen in determined in clinical laboratories, the sta-
ruminants that ingest large amounts of tus of the bicarbonate buffer system is used
carbohydrates, usually grain, over a to evaluate overall acid‐base balance. The
short period. The sudden ingestion of primary cause of acidosis or alkalosis is
the concentrated carbohydrates alters routinely diagnosed by evaluation of the
the microbial population in the rumen, bicarbonate buffer system.
favoring the rapid growth of organisms Metabolic alkalosis is a primary
that produce lactic acid. The rapid increase in bicarbonate ions. Causes
increase in lactic acid absorption into include excessive ingestion of alkaline salts
the blood overwhelms the ability of the or gastric vomiting, during which hydro-
pH regulatory systems, and systemic chloric acid is lost from the body fluids.
acidosis develops. The body compensates for metabolic alka-
losis by hypoventilation to retain carbon
dioxide and by increasing urinary bicarbo-
Classification of Alkalosis and Acidosis nate excretion.
and Compensation Metabolic acidosis is a primary
decrease in bicarbonate ions. Causes
Alkalosis is a condition in which the pH of include: (1) excessive loss of bicarbonate
body fluids (including blood) is abnormally via diarrhea (e.g., calf scours); (2) excessive
high, and acidosis is a condition in which formation of metabolic acids as a result of
the pH is abnormally low. Acidosis or metabolic disturbances (e.g., diabetes mel-
alkalosis can be classified as being either litus, starvation, and lactic acidosis during
metabolic or respiratory, to indicate the shock); (3) inability of the kidneys to
cause of the pH imbalance. The term respir- excrete acid (e.g., renal failure); and (4)
atory refers to acid‐base imbalances that absorption of excess acid from the gastro-
come about as a result of primary or initial intestinal tract (e.g., ruminal acidosis). The
changes in carbon dioxide levels. The term body compensates for metabolic acidosis
metabolic refers to all other causes of acid‐ by hyperventilation and excretion of a
base imbalances. more acid urine if possible.