Which part of the Loop of Henle is more permeable to water?

Correct Answer: B

Rationale: The thin descending limb of the Loop of Henle is highly permeable to water due to its numerous aquaporin-1 channels, allowing water to exit into the hyperosmotic medullary interstitium, concentrating the filtrate. The thick ascending limb actively reabsorbs Na⁺ and Cl⁻ but is impermeable to water, diluting the filtrate. The thin ascending limb has limited water permeability, and there's no ‘thick descending limb,' making B the correct answer.

Correct Answer: A

Rationale: Antidiuretic hormone (ADH) increases water permeability in the distal tubule and collecting duct by inserting aquaporin-2 channels, allowing water reabsorption to concentrate urine. It doesn't affect urea in the PCT (B), all nephron parts (C), or NaCl in the descending limb (D), which is water-permeable, making A correct.

Correct Answer: C

Rationale: Chemical buffer systems neutralize H⁺ instantly: phosphate (HPO₄²⁻/H₂PO₄⁻), bicarbonate (HCO₃⁻/H₂CO₃), and proteins (e.g., hemoglobin). The respiratory system (C) regulates CO₂ via ventilation, a physiological mechanism, not a chemical buffer, acting over minutes, not instantly, making C the exception.

Correct Answer: B

Rationale: Middle age (roughly 40-65) involves reevaluating life, often rediscovering satisfaction in relationships (B), per Erikson's generativity vs. stagnation stage, focusing on legacy and connection. Learning (A) is earlier, spirituality (C) varies, and risk-taking (D) is more adolescent, making B the primary task.

Correct Answer: B

Rationale: Adolescents (B) face peer pressure and busy schedules (e.g., school, sports), delaying voiding and risking habits like holding urine. Infants/toddlers (A) lack control, middle-aged adults (C) focus on work/health, and older adults (D) face physical issues, making B the group affected by these social factors.