Renin is secreted from the juxtaglomerular cells that surround the renal afferent aerioles.Aldosterone secretion is regulated the renin-angiotensin system in a feedback manner.Angiotensin II has a generalized vasoconstrictor action. A drop in ECF volume or intra-aerial vascular volume leads to a reflex increase in renal nerve discharge and decreases renal aerial pressure. Both changes increase renin secretion, and the angiotensin II formed by the action of renin increases the rate of secretion of aldosterone. The aldo- sterone causes Na+ and, secondarily, water retention, expanding ECF volume, and shutting off the stimulus that initiated increased renin secretion.renin causes renal vasoconstriction with decreased glomerular filtration and renal blood flow. Ref:-ganong, pg num:- 598, 370,675