ABSTRACT
More than 90% supplies the cortex via the renal artery, and less than 10% supplies the renal capsule and renal adipose tissue. The renal artery enters each kidney at the hilum and divides into several branches. Autoregulation describes the ability to maintain a constant renal blood flow (RBF) over a wide range of mean arterial pressures or tissue perfusion pressures (PP) from 90–200 mmHg. The rate of flow through the tubules feeds back negatively to affect glomerular filtration. Renal sympathetic nerve stimulation results in vasoconstriction of afferent arterioles thereby reducing RBF. An increase in perfusion pressure results in smooth muscle contraction and an increase in the renal vascular resistance, so maintaining a constant blood flow. RBF can be calculated by plasma clearance of para-aminohippuric acid, as a modification of the Fick principle. Renal prostaglandins attenuate sympathetic-induced vasoconstriction through vasodilation, thereby increasing RBF.
