Which of the following best describes the role of the macula densa cells?

The role of the macula densa cells is primarily to detect sodium concentration in the filtrate that flows through the renal tubules. These specialized cells are located in the distal convoluted tubule of the nephron and play a crucial role in the regulation of kidney function and blood pressure.

When sodium concentration in the filtrate decreases, the macula densa cells respond by signaling the juxtaglomerular cells to increase the secretion of renin, which ultimately leads to the production of angiotensin II. This response facilitates a series of physiological changes aimed at restoring blood volume and pressure, including increasing sodium reabsorption and stimulating aldosterone secretion from the adrenal glands. Thus, the detection of sodium concentration not only plays an integral role in kidney function but also in the overall regulation of fluid balance and blood pressure in the body.