ABSTRACT
Resistance vessels begin with the interlobular arteries, which give rise to lateral afferent arteriolar branches, and terminate in afferent arterioles in the superficial cortex. Near the vascular pole of the glomeruli, the smooth muscle cells of afferent arterioles are modified to renin granule-containing epithelioid cells that contain rudimentary myofibrils. Within the glomerulus, the capillaries converge to form the efferent arteriole. The intraglomerular portion of the efferent arteriole is surrounded by mesangial cells. Upon exit from the glomerulus, the efferent arteriole is encircled by a relatively sparse single layer of smooth muscle cells. While the combined weight of the kidneys is only 300 g, they receive one fifth of the cardiac output. Glomerular filtration, which is dependent on the high blood flow, is the principal process underlying the clearance function of the kidney. The glomerular filtration rate remains relatively constant despite variations in renal perfusion pressure.
