Which part of the nephron concentrates urine during reabsorption?

Which part of the nephron concentrates urine during reabsorption?

• A. Loop of Henle
• B. Bowman's capsule
• C. Collecting duct
• D. Glomerulus

Answer: (A)

Concentration of urine relies on the kidney’s ability to create a medullary osmotic gradient through the loop of Henle, a setup that uses a countercurrent flow to drive water reabsorption. As filtrate moves down the descending limb, it encounters an increasingly hyperosmotic interstitium, so water leaves by osmosis and the filtrate becomes more concentrated. The ascending limb, in contrast, actively pumps out salts but is impermeable to water, which dilutes the filtrate and helps build the gradient in the surrounding tissue. This established gradient is what allows water reabsorption from the collecting duct later on, producing concentrated urine when antidiuretic hormone is present. The loop of Henle is the site where significant water reabsorption occurs to concentrate the filtrate, setting up the conditions for final urine concentration. Bowman's capsule and the glomerulus are primarily filtration structures, not sites of concentrating reabsorption, and the collecting duct carries out the final step of water reabsorption under hormonal control.

Concentration of urine relies on the kidney’s ability to create a medullary osmotic gradient through the loop of Henle, a setup that uses a countercurrent flow to drive water reabsorption. As filtrate moves down the descending limb, it encounters an increasingly hyperosmotic interstitium, so water leaves by osmosis and the filtrate becomes more concentrated. The ascending limb, in contrast, actively pumps out salts but is impermeable to water, which dilutes the filtrate and helps build the gradient in the surrounding tissue. This established gradient is what allows water reabsorption from the collecting duct later on, producing concentrated urine when antidiuretic hormone is present. The loop of Henle is the site where significant water reabsorption occurs to concentrate the filtrate, setting up the conditions for final urine concentration. Bowman's capsule and the glomerulus are primarily filtration structures, not sites of concentrating reabsorption, and the collecting duct carries out the final step of water reabsorption under hormonal control.