<Tr> <Td> </Td> <Td> This article includes a list of references, related reading or external links, but its sources remain unclear because it lacks inline citations . Please help to improve this article by introducing more precise citations . (May 2015) (Learn how and when to remove this template message) </Td> </Tr> <P> The juxtaglomerular cells (JG cells, or granular cells) are cells in the kidney that synthesize, store, and secrete the enzyme renin . They are specialized smooth muscle cells mainly in the walls of the afferent arterioles, and some in the efferent arterioles, that deliver blood to the glomerulus . In synthesizing renin, they play a critical role in the renin - angiotensin system and thus in autoregulation of the kidney . </P> <P> Juxtaglomerular cells secrete renin in response to a drop in pressure detected by stretch receptors in the vascular walls, or when stimulated by macula densa cells . Macula densa cells are located in the distal convoluted tubule, and stimulate juxtaglomerular cells to release renin when they detect a drop in sodium concentration in tubular fluid . Together, juxtaglomerular cells, extraglomerular mesangial cells and macula densa cells comprise the juxtaglomerular complex . </P> <P> In appropriately stained tissue sections, juxtaglomerular cells are distinguished by their granulated cytoplasm . </P>

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