What is the main role of the juxtaglomerular apparatus in the kidney?

The main role of the juxtaglomerular apparatus (JGA) in the kidney is to regulate blood flow and pressure. This specialized structure consists of granular cells located in the walls of the afferent arterioles and macula densa cells in the distal convoluted tubule. The JGA functions primarily to monitor blood pressure in the afferent arterioles and the sodium concentration in the filtrate.

When blood pressure drops, the granular cells of the JGA release renin, an enzyme that initiates the renin-angiotensin-aldosterone system (RAAS). This system works to increase blood pressure by promoting vasoconstriction, stimulating the release of aldosterone (which increases sodium reabsorption and therefore water retention), and triggering thirst. Therefore, the JGA plays a critical role in ensuring that blood pressure remains within normal limits, alongside maintaining adequate blood flow to the nephron for optimal kidney function.

In contrast, activities like filtering blood, producing urine, and reabsorbing glucose are indeed functions associated with the kidneys, but they are not specifically attributed to the juxtaglomerular apparatus. The filtration of blood and urine production is primarily handled by the glomeruli and nephron tub