Replace the typical smooth muscle cells of the tunica media of the artery. A decrease in afferent arterial volume secondary to low perfusion pressure results in the release of renin. Renin is an enzyme that is released into the blood and acts upon blood proteins to produce a potent vasoconstrictor, angiotensin, which can, under abnormal conditions, elevate blood pressure to dangerous levels. Hypertension of renal origin in humans can be cured by removal of the diseased or ischemic kidney. Renin also affects blood volume and osmolarity by initiating a chain of events leading to the release of the hormone aldosterone by the cells of the zona glomerulosa of the adrenal cortex.
Aldosterone acts upon the renal tubules to enhance sodium reabsorption.
See Plates 116 and 237 . A group of specialized cells of the straight portion of the distal tubule, in contact with the afferent arteriole and contiguous with the juxtaglomerular cells. The cells are taller, thinner, and tightly packed compared to other distal tubule cells. These cells are functionally related to the juxtaglomerular cells, although their exact role is undefined. The macula densa marks the origin of the convoluted portion of the distal tubule.