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Correct answers of these all
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This is a First MBBS Physiology MCQ paper with 20 questions. Let me answer all of them directly from my medical knowledge - these are standard physiology questions.
Here are the correct answers for all 20 questions:
First M.B.B.S. (Main) Exam - August 2025 - Physiology Paper I
Answer Key
| Q. No. | Question (Brief) | Correct Answer |
|---|---|---|
| i | 19-yr male, tall stature, gynecomastia, small testes, 47 XXY | C) Klinefelter syndrome |
| ii | Breastfeeding woman, no menstruation - hormone inhibiting GnRH | C) Prolactin |
| iii | Fatigue, hyperpigmentation, hyponatremia, hyperkalemia - deficient hormone | A) Cortisol |
| iv | Exophthalmos, tremors, low TSH, sweating, weight loss, palpitations - elevated hormone | B) T3 |
| v | Can't maintain balance, eyes closed, feet together - positive Romberg - lesion site | C) Posterior column |
| vi | Speaks fluently but can't understand language - lesion site | C) Wernicke's area |
| vii | 70-yr woman, right eye down and out, dilated pupil, double vision - nerve affected | C) CN III |
| viii | Loss of taste in anterior two-thirds of tongue - nerve involved | D) Lingual (Chorda tympani branch of facial, carried by lingual nerve) |
| ix | Prostate cancer - hormone most directly promoting growth | A) Testosterone |
| x | Post-thyroid surgery, carpopedal spasm, numbness around lips - most likely explanation | B) Hypoparathyroidism |
| xi | Fasting hyperglycemia, central obesity, buffalo hump, high cortisol, low ACTH | A) Pituitary adenoma |
| xii | Lambert-Eaton syndrome - weakness improves with activity - defect in | B) Voltage-gated calcium channels |
| xiii | Duchenne muscular dystrophy - deficient protein | C) Dystrophin |
| xiv | Neurotoxin blocks voltage-gated Na+ channels - effect on nerve conduction | C) Action potential fails to propagate |
| xv | 65-yr, resting tremors, slow voluntary movements - lesion site | B) Basal ganglia |
| xvi | Bitemporal hemianopia - lesion at | B) Optic chiasma |
| xvii | Rigor mortis occurs because of | D) Sudden influx of calcium into the muscle |
| xviii | Blood-brain barrier (BBB) is least permeable to | D) Proteins |
| xix | Lesion in spinothalamic tract - loss of | B) Pain and temperature sensation |
| xx | First visible sign of puberty in males | A) Testicular enlargement |
Key Explanations for Tricky Questions:
Q.ii - Prolactin directly inhibits GnRH from the hypothalamus (not progesterone, oxytocin, or estrogen), explaining lactational amenorrhea.
Q.iii - Low cortisol (primary adrenal insufficiency / Addison's disease) causes hyponatremia, hyperkalemia, fatigue, and hyperpigmentation (due to compensatory high ACTH stimulating melanocytes).
Q.viii - Taste from the anterior 2/3 of the tongue travels via chorda tympani (branch of CN VII/Facial), but it is physically carried within the lingual nerve (branch of CN V3). The answer is Lingual nerve as it conveys these fibers to the tongue.
Q.xi - High cortisol + LOW ACTH points to an adrenal source (not pituitary), which would be Adrenal adenoma (Cushing's syndrome). Wait - if ACTH is low, it means the cortisol is being produced autonomously by the adrenal gland, so the answer is B) Adrenal adenoma.
(Correction for Q.xi: Low ACTH + high cortisol = adrenal adenoma, not pituitary adenoma)
Q.xvii - Rigor mortis: After death, ATP is depleted. Without ATP, calcium is not pumped back into the sarcoplasmic reticulum, causing sustained actin-myosin cross-bridge formation (not detachment). Option D - "sudden influx of calcium into the muscle" best captures the mechanism.
Q.xix - The spinothalamic tract carries pain and temperature (and crude touch). A lesion causes loss of pain and temperature sensation on the contralateral side.
Q.xx - The first sign of puberty in males is testicular enlargement (due to FSH-driven seminiferous tubule growth), not facial hair or voice deepening.
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