Question

when macula densa cells experience increased na+ concentration in the filtrate, they respond by
multiple choice

increasing aldosterone secretion.

increasing renin secretion

decreasing renin secretion.

increasing afferent arteriole constriction.

decreasing urine production.

Explanation:

Macula densa cells are part of the juxtaglomerular apparatus. When they detect increased \(Na^{+}\) in the filtrate, it indicates that the glomerular filtration rate (GFR) is likely too high. Renin secretion is part of the renin - angiotensin - aldosterone system (RAAS). An increase in \(Na^{+}\) in the filtrate (suggesting high GFR) leads to a decrease in renin secretion. Aldosterone secretion is regulated by angiotensin II (which is influenced by renin). Increasing afferent arteriole constriction would decrease GFR further, but the macula densa's response to high \(Na^{+}\) (high GFR) is not to increase afferent arteriole constriction. Decreasing urine production would be a result of processes like increased water reabsorption (e.g., via antidiuretic hormone), not directly the macula densa's response to high \(Na^{+}\) in the filtrate.

Answer:

decreasing renin secretion.