USA Surgery Today

The major role of the kidney is to maintain body water and electrolyte homeostasis. The first step in this process is the production of the glomerular filtrate from the renal plasma. The glomerular filtration rate (GFR) is dependent on renal plasma flow, which in turn is dependent on blood pressure and circulating volume. The kidneys receive about 20% to 30% of the cardiac output, and this is maintained over a wide range of blood pressures through changes in renal vascular resistance. Numerous hormones play a role in this autoregulation, including the vasodilators (prostaglandins E and I₂, dopamine, and nitric oxide) and the vasoconstrictors (angiotensin II, thromboxane, adrenergic stimulation, and endothelin). Congestive heart failure and volume contraction severely limit the kidney’s ability to maintain autoregulation in the face of changes in blood pressure.