The region known as the macula densa is part of

The region known as the macula densa is part of excretory system.

More precisely, macula densa is a structure located in the kidney, in the wall of the distal tubule. The macula densa is composed of tightly packed specialized cells on the place where the distal tubule touches the glomerulus.

The role of this structure is to detect changes in concentration of sodium chloride and to send a signal to the afferent arterioles (to change blood pressure) or to the juxtaglomerular cells (renin release).