Answer
🧠 Nephron Tubule Diagram Explanation
🔍 Understanding the Functions
The nephron consists of various tubules that help in reabsorption and secretion of substances. Two important segments are:
- Proximal Tubule (P): Major site of reabsorption and some secretion.
- Distal Tubule (D): Fine-tunes ion levels and regulates acid-base balance.
🔬 Key Functions
| Segment | Reabsorbed | Secreted |
|---|---|---|
| Proximal Tubule (P) | NaCl, HCO₃⁻, H₂O | H⁺, NH₃ |
| Distal Tubule (D) | NaCl, H₂O, HCO₃⁻ | H⁺, K⁺ |
📝 Option Analysis
| Option | Proximal Tubule (P) | Distal Tubule (D) | Verdict |
|---|---|---|---|
| (1) | HCO₃⁻, NaCl, H₂O reabsorbed; H⁺ secreted | NaCl, H₂O, HCO₃⁻ reabsorbed; K⁺, H⁺ secreted | ✅ Correct |
| (2) | HCO₃⁻, NaCl, H₂O reabsorbed; NH₃ secreted | NaCl, H₂O, HCO₃⁻ reabsorbed; K⁺, H⁺ secreted | 🔸 Partially Correct |
| (3) | HCO₃⁻, NaCl, H₂O reabsorbed; H⁺, NH₃ secreted | H₂O, HCO₃⁻ reabsorbed; NaCl, H⁺ wrongly placed | ❌ Incorrect |
| (4) | NaCl, HCO₃⁻ reabsorbed; H₂O incorrectly secreted | NH₃ reabsorbed (wrong); H₂O secreted (wrong) | ❌ Incorrect |
✅ Final Answer
Correct Answer: (1) – Matches known physiological processes of the nephron.
📌 Takeaways
- NaCl and HCO₃⁻ are reabsorbed in both P and D segments.
- Water (H₂O) is reabsorbed in both tubules (not secreted).
- H⁺ is secreted in both P and D for pH balance.
- NH₃ is secreted in P; K⁺ is secreted in D.