Final answer:
The macula densa, part of the distal convoluted tubule, senses changes in blood pressure and signals the juxtaglomerular cells to release renin, which helps regulate blood pressure.
Step-by-step explanation:
The part of the kidney that senses changes in blood pressure is the macula densa, which is found in the distal convoluted tubule (DCT) forming the juxtaglomerular apparatus (JGA). The macula densa cells monitor the sodium concentration and fluid flow through the DCT and provide feedback to the juxtaglomerular cells, which are modified smooth muscle cells of the afferent arteriole. These juxtaglomerular cells can release renin, a regulatory enzyme, in response to cues from the macula densa about changes in blood pressure or fluid flow. This mechanism plays a critical role in maintaining blood pressure within a healthy range.