Final answer:
The juxtaglomerular cells are the specialized cells that release renin and play a significant role in regulating blood pressure, responding to changes detected by the macula densa in the distal convoluted tubule.
Step-by-step explanation:
The specialized cells surrounding the afferent arteriole near the distal tubule that play a role in blood pressure regulation by releasing the hormone renin are known as juxtaglomerular cells. These cells are modified smooth muscle cells of the afferent arteriole and secrete renin in response to a drop in blood pressure. Renin release is also influenced by signals from the macula densa, which are cells located at the distal convoluted tubule (DCT) that monitor the sodium concentration in the filtrate. In the context of the renin-angiotensin-aldosterone system (RAAS), renin acts on angiotensinogen to produce angiotensin I, which is then converted to angiotensin II, a potent vasoconstrictor that increases blood pressure and stimulates aldosterone release, leading to water and sodium retention.