Which nephron structure is primarily involved in final urine concentration and can be influenced by hormones?

Which nephron structure is primarily involved in final urine concentration and can be influenced by hormones?

• A. Proximal convoluted tubule
• B. Distal convoluted tubule
• C. Loop of Henle
• D. Collecting duct

Answer: (D)

Final urine concentration hinges on how permeable the nephron is to water as filtrate flows through. The collecting duct is the primary site where hormones adjust this permeability. Antidiuretic hormone makes Aquaporin water channels appear in the collecting duct’s walls, so water can be reabsorbed from the filtrate into the surrounding medullary tissue. This reabsorption concentrates the urine. If ADH is low or absent, the collecting duct remains relatively water-impermeable, and urine stays dilute. The loop of Henle sets up the medullary osmotic gradient that makes concentration possible, but the final adjustment is controlled in the collecting duct. The proximal tubule reabsorbs most water and solutes before this point without hormonal tuning for final concentration, whereas the distal tubule contributes to fine-tuning, but the key hormone-driven step for concentrating urine occurs in the collecting duct.

Final urine concentration hinges on how permeable the nephron is to water as filtrate flows through. The collecting duct is the primary site where hormones adjust this permeability. Antidiuretic hormone makes Aquaporin water channels appear in the collecting duct’s walls, so water can be reabsorbed from the filtrate into the surrounding medullary tissue. This reabsorption concentrates the urine. If ADH is low or absent, the collecting duct remains relatively water-impermeable, and urine stays dilute. The loop of Henle sets up the medullary osmotic gradient that makes concentration possible, but the final adjustment is controlled in the collecting duct. The proximal tubule reabsorbs most water and solutes before this point without hormonal tuning for final concentration, whereas the distal tubule contributes to fine-tuning, but the key hormone-driven step for concentrating urine occurs in the collecting duct.