MBBS Physiology 2 — Questions and Answers
Question 1: Which segment of the nephron is impermeable to water under all conditions?
- Proximal convoluted tubule
- Thin descending loop of Henle
- Thick ascending loop of Henle (Correct answer)
- Collecting duct
Correct answer: Thick ascending loop of Henle
The thick ascending limb of the loop of Henle is always impermeable to water but actively transports NaCl, creating the medullary concentration gradient.
Question 2: What is the normal pH range of arterial blood?
- 7.25–7.35
- 7.35–7.45 (Correct answer)
- 7.45–7.55
- 7.30–7.40
Correct answer: 7.35–7.45
Normal arterial blood pH is 7.35–7.45, maintained primarily by the bicarbonate buffer system, lungs, and kidneys.
Question 3: Which hormone causes water reabsorption in the collecting duct by inserting aquaporin-2 channels?
- Aldosterone
- Atrial natriuretic peptide
- Antidiuretic hormone (ADH) (Correct answer)
- Parathyroid hormone
Correct answer: Antidiuretic hormone (ADH)
ADH (vasopressin) binds V2 receptors in the collecting duct, triggering aquaporin-2 insertion and increasing water reabsorption.
Question 4: Which phase of the cardiac action potential is responsible for the plateau in ventricular myocytes?
- Phase 0 — rapid depolarization
- Phase 1 — early repolarization
- Phase 2 — plateau (Correct answer)
- Phase 3 — rapid repolarization
Correct answer: Phase 2 — plateau
Phase 2 (plateau) is caused by sustained Ca2+ influx through L-type calcium channels balanced by K+ efflux, preventing early repolarization.
Question 5: What is the primary stimulus for erythropoietin (EPO) secretion?
- Low hemoglobin concentration
- High altitude exposure
- Tissue hypoxia detected by renal peritubular cells (Correct answer)
- Low serum iron
Correct answer: Tissue hypoxia detected by renal peritubular cells
EPO is secreted by peritubular interstitial cells of the kidney in response to tissue hypoxia, mediated by HIF-1α transcription factor.
Question 6: Which of the following best describes the role of surfactant in the lungs?
- Increases surface tension to stabilize alveoli
- Reduces surface tension to prevent alveolar collapse (Correct answer)
- Facilitates oxygen diffusion across the alveolar membrane
- Neutralizes inhaled pathogens
Correct answer: Reduces surface tension to prevent alveolar collapse
Surfactant (dipalmitoyl phosphatidylcholine) reduces alveolar surface tension, preventing collapse during expiration and reducing work of breathing.
MBBS Physiology 2
Which segment of the nephron is impermeable to water under all conditions?