Anatomy of the juxtaglomerular apparatus

The juxtaglomerular cells in the wall of the afferent arteriole secrete renin into the lumen of the afferent arteriole and the renal lymph. Stretch receptors in the afferent arteriole, the sympathetic nerves ending in the juxtaglomerular cells, and the composition of the tubular fluid reaching the macula densa all contribute to the regulation of renin secretion.