What are the vertical segments of the nephron primarily focused on?

What are the vertical segments of the nephron primarily focused on?

• A. Volume and concentration of the urine.
• B. Reabsorbing amino acids and glucose.
• C. Filtration of blood.
• D. Secretion of hormones.

Answer: (A)

These vertical segments—the descending and ascending limbs of the loop of Henle—are specialized to generate and maintain a concentration gradient in the medulla, which drives urine concentration and volume adjustments. The descending limb is highly permeable to water, so as filtrate moves deeper into the medulla it loses water to the surrounding tissue and becomes more concentrated. The ascending limb, in contrast, is impermeable to water but actively reabsorbs ions (like Na+, K+, and Cl−) out of the filtrate, diluting it as it ascends and building the medullary osmotic gradient. This arrangement prepares the way for the collecting ducts to reabsorb water under hormonal control, allowing the body to regulate how much urine is produced and how concentrated it is.

These vertical segments—the descending and ascending limbs of the loop of Henle—are specialized to generate and maintain a concentration gradient in the medulla, which drives urine concentration and volume adjustments. The descending limb is highly permeable to water, so as filtrate moves deeper into the medulla it loses water to the surrounding tissue and becomes more concentrated. The ascending limb, in contrast, is impermeable to water but actively reabsorbs ions (like Na+, K+, and Cl−) out of the filtrate, diluting it as it ascends and building the medullary osmotic gradient. This arrangement prepares the way for the collecting ducts to reabsorb water under hormonal control, allowing the body to regulate how much urine is produced and how concentrated it is.