<Li> Decrease in NaCl concentration at the macula densa, often due to a decrease in glomerular filtration rate </Li> <P> Extraglomerular mesangial cells are located in the junction between the afferent and efferent arterioles, but their significance in this location is unknown . Renin is also found in these cells . </P> <P> At the point where the afferent arterioles enter the glomerulus and the efferent arteriole leaves it, the tubule of nephron touches the arterioles of the glomerulus from which it rose . At this location, thick ascending limb of loop of Henle, there is a modified region of tubular epithelium called the Macula densa . Cells in the macula densa respond to changes in the sodium chloride levels in the distal tubule of the nephron via the tubuloglomerular feedback (TGF) loop . </P> <P> The macula densa's detection of elevated sodium chloride, which leads to a decrease in GFR, is based on the concept of purinergic signaling . An increase in the salt concentration causes several cell signals to eventually cause the adjacent afferent arteriole to constrict . This decreases the amount of blood coming from the afferent arterioles to the glomerular capillaries, and therefore decreases the amount of fluid that goes from the glomerular capillaries into the Bowman's space (the glomerular filtration rate (GFR)). </P>

The structure known as the juxtaglomerular apparatus is located near which of the following