FIRST MBBS Physiology Paper II - July 2026

Answers According to Guyton and Hall Textbook of Medical Physiology

MCQ Section (20 x 1 = 20 marks)

Q1. 64-year-old woman: MAP = 120 mmHg, HR = 60 bpm, SV = 50 mL, RAP = 0 mmHg. What is TPR (mmHg/mL/min)?

• Cardiac Output (CO) = HR × SV = 60 × 50 = 3000 mL/min
• TPR = (MAP - RAP) / CO = (120 - 0) / 3000 = 0.04 mmHg/mL/min

Q2. After total gastrectomy for pyloric malignancy - lifelong supplement of?

Q3. Rejection of transplanted kidney is mediated by?

Q4. 25-year-old athlete: HR = 60 bpm, BP = 118/68 mmHg. EDV = 150 mL, end-systolic volume = 60 mL. Student's mean blood pressure is?

• Pulse Pressure = Systolic - Diastolic = 118 - 68 = 50 mmHg
• MAP = 68 + (1/3 × 50) = 68 + 16.7 ≈ 73 mmHg ✓

Q5. Determination of specific gravity of urine indicates more of?

Q6. Most effective buffer system of the body?

1. It is present in large concentrations in the ECF
2. Both components (CO₂ and HCO₃⁻) are independently regulated by lungs and kidneys respectively
3. It is an open system - this makes it far more effective than a closed buffer system

Q7. Platelet count 212,000/µL and bleeding time 12 minutes indicate?

• Normal platelet count (150,000-400,000/µL) rules out thrombocytopenia
• Prolonged bleeding time (normal: 1-6 minutes) with a normal platelet count indicates a qualitative platelet defect (defective platelet function) - such as von Willebrand disease, Glanzmann thrombasthenia, or aspirin effect
• The combination of normal count + prolonged bleeding time = platelet function disorder

Q8. Vascular bed with maximum vasoconstriction in person finishing a 10 km run?

Q9. Antigen from food ingested by Peyer's patches - activates generation/secretion - same antigen again?

Q10. 40-year-old woman: severe anemia, CO = 12.5 L/min, pulmonary artery O₂ = 250 mL/L, pulmonary vein O₂ = 160 mL/L. Oxygen concentration in pulmonary artery = ?

• VO₂ = CO × (CaO₂ - CvO₂)
• CaO₂ - CvO₂ = VO₂ / CO

• The question states cardiac output = 12.5 L/min (12.5 × 1000 = 12,500 mL/min)
• O₂ consumption in severe anemia...

Q11. Renal function study - which intervention would MOST LIKELY decrease RPF and GFR?

• A. Constrict the afferent arteriole → decreases both RPF and GFR
• B. Increase filtration fraction (FF)
• C. Dilation of afferent arteriole
• D. Obstruction to the ureter

Q12. Hirschsprung's disease - pathogenesis involves congenital absence of which cells?

Q13. 55-year-old man with acute chest pain diagnosed with inferior myocardial infarction. ECG leads?

Q14. Normal expiration and forced expiration - which processes?

• Normal (quiet) expiration is a passive process driven by the elastic recoil of the lungs and chest wall. No muscles contract - it is entirely passive.
• Forced expiration requires active muscle contraction - primarily the abdominal muscles (rectus abdominis, external/internal obliques, transversus abdominis) and the internal intercostal muscles, which pull the ribs downward and inward, forcibly decreasing thoracic volume.

Q15. Which endocrine disorder does NOT cause hypertension?

• Myxedema (hypothyroidism): can cause mild hypertension (diastolic)
• Acromegaly (excess GH): causes hypertension due to sodium retention
• Addison's disease (adrenocortical insufficiency): causes hypotension due to aldosterone deficiency → sodium loss → volume depletion. This is the only one that does NOT cause hypertension.
• Pheochromocytoma: classic cause of severe episodic hypertension (excess catecholamines)

Q16. HCl secretion is stimulated by?

1. Gastrin (most potent hormonal stimulant) - secreted by G cells in the antrum
2. Histamine - acts on H₂ receptors on parietal cells
3. Acetylcholine - vagal stimulation

Q17. Oxygen (21% of inspired air) exerts a partial pressure of?

• Atmospheric pressure = 760 mmHg
• O₂ fraction = 21% = 0.21
• PO₂ in dry inspired air = 760 × 0.21 = 159.6 ≈ 160 mmHg

Q18. Migrating motor complex is regulated by?

Q19. Complete transection at mid-pons level results in?

• The pneumotaxic center (upper pons) is disconnected from the apneustic center (lower pons)
• The apneustic center, now released from pneumotaxic inhibition, drives prolonged inspiratory gasps
• This produces apneusis - sustained inspiratory cramps with very brief expirations

Q20. Blood flow per unit gram of tissue/min is highest for?

ANSWER KEY SUMMARY

Long Essay (Q2) - Functions of Liver, Bile Secretion, Jaundice (Brief outline per Guyton)

• Metabolic: carbohydrate metabolism (glycogenesis, glycogenolysis, gluconeogenesis), fat metabolism (beta-oxidation, lipogenesis, ketone synthesis), protein metabolism (deamination, urea synthesis, plasma protein synthesis)
• Secretory: bile production (600-1000 mL/day)
• Storage: glycogen, vitamins A, D, B12, iron
• Detoxification: drugs, hormones, ammonia → urea
• Hematopoiesis in fetal life
• Phagocytosis by Kupffer cells
• Clotting factors synthesis (I, II, V, VII, IX, X)

• Bile is secreted by hepatocytes into bile canaliculi; modified by ductal epithelium
• Primary bile acids (cholic, chenodeoxycholic) conjugated with glycine/taurine
• Regulation: Secretin stimulates HCO₃⁻-rich ductal secretion; CCK causes gallbladder contraction; Gastrin mildly stimulates; enterohepatic circulation maintains bile acid pool

• Prehepatic (hemolytic): excess bilirubin production from RBC breakdown → unconjugated hyperbilirubinemia
• Hepatic (hepatocellular): damaged hepatocytes cannot conjugate or excrete bilirubin → mixed hyperbilirubinemia
• Posthepatic (obstructive): blocked bile ducts → conjugated bilirubin regurgitates into blood → dark urine, pale stools, conjugated hyperbilirubinemia

Short Answers (Q3) - "Explain Why" (5 x 3 = 15)

Answers According to U.N. Satyanarayana's Biochemistry

MCQ Section (20 x 1 = 20 marks)

Q1. Patient with weight gain, cold intolerance, lethargy. TSH raised, free T4 low. Diagnosis?

Q2. Gene undergoes deletion of a single nucleotide, altering the reading frame of all codons downstream. This mutation is called?

• Missense mutation: one base substitution changes one amino acid
• Silent mutation: base substitution produces same amino acid (degenerate code)
• Nonsense mutation: base change produces a stop codon
• Frameshift: deletion/insertion of non-multiple-of-3 nucleotides shifts the entire reading frame

Q3. 2-year-old child, low socioeconomic family, generalized edema, fatty liver, hypoalbuminemia but body weight close to normal. Most likely diagnosis?

Q4. Young boy: hyperextensible joints, unusually elastic and fragile skin, easy bruising. Defect in synthesis of?

• Collagen provides tensile strength to skin, tendons, joints, and blood vessels
• Defects in collagen (Type I, III, or V) result in hyperextensible skin, hypermobile joints, and easy bruising
• Elastin provides elasticity - defects cause problems with recoil, not tensile strength
• Fibronectin is a cell adhesion glycoprotein
• Proteoglycans are ground substance components

Q5. Patient with acute viral hepatitis shows elevated conjugated AND unconjugated bilirubin, markedly raised ALT/AST, only mildly raised alkaline phosphatase. This pattern is typical of?

Q6. 60-year-old diabetic patient: serum creatinine 3.5 mg/dL. Most reliable test for GFR estimation?

• Creatinine clearance is the most reliable test for estimating GFR because creatinine is freely filtered at the glomerulus, not reabsorbed, and only minimally secreted
• Formula: Ccr = (U × V) / P, where U = urinary creatinine, V = urine volume/min, P = plasma creatinine
• Serum creatinine alone rises only when GFR falls to ~50% - it is not sensitive enough alone
• Blood urea is affected by protein intake, hydration, hepatic function - less reliable
• Serum uric acid reflects purine metabolism, not GFR

Q7. 6-month-old infant given DPT vaccine and develops protective antibody response after a few days. This immunity is?

Q8. Young patient with polyuria, polydipsia, weight loss, random blood glucose 350 mg/dL. Deficient hormone?

• The classic triad of polyuria, polydipsia, and weight loss with hyperglycemia (350 mg/dL, normal < 200 mg/dL random) = Diabetes Mellitus
• Insulin deficiency is the hallmark - absolute deficiency in Type 1 DM or relative deficiency in Type 2
• Without insulin, glucose cannot enter cells → hyperglycemia → osmotic diuresis (polyuria) → polydipsia → cells starve despite high blood glucose → catabolism → weight loss
• Glucagon, cortisol, and growth hormone are counter-regulatory (they raise blood glucose) - excess of these could cause hyperglycemia but the primary deficient hormone here is insulin

Q9. Preterm neonate on prolonged O₂ therapy given Vitamin E to prevent free-radical damage. Vitamin E acts as?

• Vitamin E (tocopherol) is the principal chain-breaking antioxidant in cell membranes
• It donates a hydrogen atom to lipid peroxyl radicals (LOO•), breaking the chain of lipid peroxidation
• Reaction: Vit E-OH + LOO• → Vit E-O• + LOOH (chain terminated)
• Vitamin E is NOT a pro-oxidant, NOT an enzyme cofactor for catalase, and NOT a chelating agent
• Catalase uses iron as cofactor; chelating agents bind metal ions; Vitamin C regenerates Vitamin E
• Satyanarayana specifically states: "Vitamin E is the most important chain-breaking antioxidant protecting cell membranes from lipid peroxidation"

Q10. 50-year-old woman with ovarian mass and ascites. Markedly elevated specific glycoprotein tumor marker?

• CA 125 (Cancer Antigen 125) is a high-molecular-weight glycoprotein tumor marker specifically associated with ovarian cancer
• It is elevated in >80% of epithelial ovarian carcinomas
• CA 19-9 is the marker for pancreatic and GI cancers
• PSA (Prostate Specific Antigen) is for prostate cancer
• AFP (Alpha-fetoprotein) is for hepatocellular carcinoma and germ cell tumors
• The clinical scenario of ovarian mass + ascites + elevated glycoprotein marker = CA 125

Q11. HIV-positive patient: CD4+ count 150 cells/µL with oral candidiasis. This indicates?

• Normal CD4+ count: 500-1500 cells/µL
• CD4+ count < 200 cells/µL = AIDS (Acquired Immunodeficiency Syndrome) by definition
• Oral candidiasis is an AIDS-defining opportunistic infection
• This patient has CD4+ 150 (< 200) + oral candidiasis = AIDS-defining immunosuppression
• Early HIV infection: CD4+ is normal or near-normal
• Window period: antibody negative despite infection (early phase)
• Immune reconstitution: occurs after starting ART when CD4+ rises

Q12. Patient with severe epigastric pain radiating to back, raised amylase AND lipase. Which has GREATER SPECIFICITY for acute pancreatitis?

• Both amylase and lipase rise in acute pancreatitis, but:
• Amylase also rises in: parotitis (mumps), intestinal obstruction, perforated peptic ulcer, renal failure, ectopic pregnancy - less specific
• Lipase is more specific because it is predominantly produced by the pancreas; it rises later but stays elevated longer (7-10 days vs 3-4 days for amylase)
• Satyanarayana states: "Lipase estimation has greater specificity (>90%) for pancreatitis compared to amylase (~70%)"
• Trypsin is not a routine serum test; alkaline phosphatase is a marker of biliary/bone disease

Q13. Laboratory technique that exponentially amplifies specific DNA segment using thermostable DNA polymerase and specific primers?

• PCR uses: thermostable Taq polymerase + two specific primers + dNTPs + template DNA
• Three steps: Denaturation (94°C) → Annealing (~55°C) → Extension (72°C) - repeated 30-40 cycles
• Result: exponential amplification (2ⁿ copies after n cycles)
• Southern blotting: DNA transferred to membrane and hybridized with probe (does NOT amplify)
• Northern blotting: for RNA analysis
• ELISA: antigen-antibody immunological assay (not DNA-based)
• PCR is unique in requiring Taq polymerase (isolated from Thermus aquaticus) - thermostable so it survives denaturation cycles

Q14. Malignant tumor degrades surrounding extracellular matrix for invasion and metastasis. This is predominantly mediated by?

• MMPs (Matrix Metalloproteinases) are a family of zinc-dependent endopeptidases that collectively degrade virtually all ECM components:
  • Collagenases (MMP-1, 8, 13): degrade fibrillar collagens
  • Gelatinases (MMP-2, 9): degrade basement membrane collagen IV
  • Stromelysins: degrade proteoglycans, fibronectin
  • Membrane-type MMPs: activate other MMPs
• Cancer cells upregulate MMPs to break down basement membrane and invade surrounding tissue
• Collagenases alone would not degrade all ECM components
• Elastase degrades elastin specifically; Hyaluronidase degrades hyaluronic acid only
• MMPs as a family provide the comprehensive degradative activity needed for metastasis

Q15. Calorific value of carbohydrate?

Q16. Normal BMR for a healthy adult man?

• Normal BMR for an adult man = 35-38 Cal/m² body surface area/hour (approximately 36 Cal/m²/hr)
• Normal for adult woman = 32-35 Cal/m²/hr (about 5-10% lower due to higher body fat)
• BMR represents energy expenditure at complete rest, post-absorptive state (12 hours fasting), thermoneutral environment
• Satyanarayana gives the standard value as 36 Cal/m²/hr for adult males
• This translates to approximately 1700-2000 Cal/day for an average adult

Q17. RDA of protein for a normal healthy adult?

• The recommended dietary allowance (RDA) for protein in a normal healthy adult = 1 g/kg body weight/day
• For a 60 kg adult = 60 g protein/day
• ICMR (Indian Council of Medical Research) recommends 1 g/kg/day for adults
• Requirements increase in: pregnancy (+15 g/day), lactation (+25 g/day), growing children (1.5-2 g/kg/day), athletes
• 0.5 g/kg is inadequate; 2-3 g/kg is therapeutic dosing for specific conditions, not the general RDA

Q18. Specific Dynamic Action (SDA) is highest for?

• SDA (also called Thermic Effect of Food / Diet-induced thermogenesis) is the increase in metabolic rate following ingestion of food, due to the energy cost of digestion, absorption, and metabolism
• SDA values:
  • Proteins: 20-30% of calories consumed (highest)
  • Carbohydrates: 5-10%
  • Fats: 4-5% (lowest)
  • Mixed diet: ~10%
• Proteins require the most metabolic energy for deamination and transamination before they can be used
• Satyanarayana specifically states: "SDA is highest for proteins (30%), intermediate for carbohydrates, and lowest for fats"

Q19. In a clinical biochemistry laboratory, AI is most useful for?

• Predictive analytics: predicting disease risk from laboratory trends
• Pattern recognition: identifying abnormal patterns in large datasets, flagging critical values, delta checks
• Automated interpretation of results
• Quality control monitoring
• AI cannot do manual pipetting, physical transport, or cleaning - these are physical tasks. AI excels at data processing and intelligent decision support.

Q20. Phase I reactions of xenobiotic metabolism mainly involve?

• Oxidation (most common) - cytochrome P450 (CYP) monooxygenase system in liver microsomes
• Reduction - azoreductases, nitroreductases
• Hydrolysis - esterases, amidases
• These introduce or unmask a reactive functional group (-OH, -NH₂, -COOH, -SH)

• Glucuronidation (UDP-glucuronosyl transferase) - most important
• Sulfation (sulfotransferases) → option A
• Acetylation (N-acetyltransferases) → option D
• Methylation, glutathione conjugation

ANSWER KEY SUMMARY