Functions of the Kidneys
The primary function of the kidneys is to
regulate the volume and composition of extracellular fluid in order to maintain a stable
chemical and physical internal environment for cells. This is accomplished by regulation
of water, electrolyte, and acid-base balance through the processes of glomerular
filtration, tubular reabsorption and tubular secretion. To maintain normal levels of water,
electrolytes and acid/base, the loss of these substances from the body must equal the gain
of each by the body.
Loss of any substance from the body occurs by excretion in
urine, feces or by insensible routes (respiration is the only significant site of
insensible loss in the dog and cat) and by consumption in metabolic reactions. The body
can "gain" substances by ingestion, parenteral administration (e.g. IV or IM
injection) or by production in a metabolic reaction.
The kidneys are responsible for excretion of metabolic
wastes including:
- uric acid which is derived from nucleic acids
- creatinine from muscle creatine
- bilirubin derived from hemoglobin
- urea nitrogen derived from dietary and endogenous proteins
The kidneys excrete many foreign chemicals including
pharmacologics and toxins.
The kidneys play an important role in the regulation of
arterial blood pressure. The following factors influence blood pressure:
- sodium and water balance
- the renin-angiotensin-aldosterone system
- vasoactive prostaglandins which are produced in the kidney
Decreased oxygen delivery to the kidney stimulates the
release of renal erythropoietic factor which acts on a liver globulin to produce
erythropoietin. Erythropoietin stimulates bone marrow stem cells to differentiate along
RBC lines.
The kidneys produce the active form of vitamin D; 1,25
dihydroxycholecalciferol.
The kidneys are capable of gluconeogenesis (glucose
production) during a prolonged fast, although this is a minor function.
The following hormones are degraded or excreted by the
kidneys:
- parathyroid hormone
- growth hormone
- secretin
- cholecystokinin
- glucagon
- gastrin
- insulin
- antidiuretic hormone
Any of these hormones may increase in circulation in the
patient with renal dysfunction if the kidney is unable to excrete or degrade the hormone.
Last Edited: Jul 26, 2007 1:51 PM
