dysfunction (i.e., Cushing’s disease). An increased serum potassium
level, hyperkalemia, occurs most often in urinary obstruction, anuria, or
acute renal disease (Bistner, 1995).
Sodium and its related anions (i.e., chloride and bicarbonate) are
primarily responsible for the osmotic attraction and retention of water in
the extracellular fluid compartments. The endothelial membrane is freely
permeable to these small electrolytes. Sodium is the most abundant
extracellular cation, however, very little is present intracellularly. The
main functions of sodium in the body include maintenance of membrane
potentials and initiation of action potentials in excitable membranes. The
sodium concentration also largely determines the extracellular osmolarity
and volume. The differential concentration of sodium is the principal
force for the movement of water across cellular membranes. In addition,
sodium is involved in the absorption of glucose and some amino acids
from the gastrointestinal tract (Lehninger, 1993). Sodium is ingested
with food and water, and is lost from the body in urine, feces, and sweat.
Most sodium secreted into the GI tract is reabsorbed. The excretion of
sodium is regulated by the renin-angiotensin-aldosterone system
(Schmidt-Nielsen, 1995).
Decreased serum sodium levels, hyponatremia, can be seen in adrenal
insufficiency, inadequate sodium intake, renal insufficiency, vomiting or
diarrhea, and uncontrolled diabetes mellitus. Hypernatremia may occur in
dehydration, water deficit, hyperadrenocorticism, and central nervous
system trauma or disease (Bistner, 1995).
Chloride is the major extracellular anion. Chloride and bicarbonate ions
are important in the maintenance of acid-base balance. When chloride in
the form of hydrochloric acid or ammonium chloride is lost, alkalosis
follows; when chloride is retained or ingested, acidosis follows. Elevated
serum chloride levels, hyperchloremia, can be seen in renal disease,
dehydration, overtreatment with saline solution, and carbon dioxide
deficit (as occurs from hyperventilation). Decreased serum chloride
levels, hypochloremia, can be seen in diarrhea and vomiting, renal
disease, overtreatment with certain diuretics, diabetic acidosis,
hypoventilation (as occurs in pneumonia or emphysema), and adrenal
insufficiency (de Morais, 1995).
As seen above, one to two milliliters of blood can give a clinician a great
insight to the way an animals’ systems are functioning. With many more
tests available and being developed every day, diagnosis becomes less
invasive to the patient. The more information that is made available to
the doctor allows a faster diagnosis and recovery for the patient.
7b9
Barrie, Joan and Timothy D. G. Watson. ?Hyperlipidemia.?
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Philadelphia: W. B. Saunders, 1995.
Bistner, Stephen l. Kirk and Bistner?s Handbook of Veterinary
Procedures and Emergency Treatment. Philadelphia: W. B.
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de Morais, HSA and William W. Muir. ?Strong Ions and Acid-Base
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Garrett, Reginald H. and Charles Grisham. Biochemistry. Fort
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Lehninger, Albert, David Nelson and Michael Cox. Principles of
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Schmidt-Nielsen, Knut. Animal Physiology: Adaptation and
environment. New York: Cambridge University Press, 1995.
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Santa Barbara: American Veterinary Publications, 1995.