Which of the following diagrams is correct with regard to the proximal (P) and distal (D) tubule of the Nephron.
Answer: (D) (d). Answer: (D) the diagram showing the correct reabsorption/secretion directions for the proximal (P) and distal (D) tubules.
- A.(a)
- B.(b)
- C.(c)
- D.(d)✓
Correct Answer
(D) (d)
Solution & Explanation
Answer: (D) the diagram showing the correct reabsorption/secretion directions for the proximal (P) and distal (D) tubules. Solution: In the PCT nearly all nutrients and 70-80% of electrolytes and water are reabsorbed, and the PCT secretes H+ and ammonia into the filtrate while absorbing HCO3- from it. In the DCT there is conditional reabsorption of Na+ and water and reabsorption of HCO3-, with selective secretion of H+, K+ and NH3. So the correct figure must show H2O/NaCl/HCO3- being reabsorbed and H+/NH3 (and K+ in DCT) being secreted in these directions; option (d) is the only diagram matching this. NCERT Reference: Ch 16, p.209, line(s) 28-48 — "PCT also helps to maintain the pH and ionic balance of the body fluids by selective secretion of hydrogen ions and ammonia into the filtrate and by absorption of HCO3"