Medical Physiology Paper II MCQs — MCQ Bank OmpathStudy

#### SCHOOL OF MEDICINE DEPARTMENT OF MEDICAL PHYSIOLOGY --- --- INSTRUCTIONS: This paper contains two sections . Section A: Short Answer Questions — Answer all questions. Section B: Structured Questions — Answer only TWO questions. --- SECTION A: SHORT ANSWER QUESTIONS (60 Marks) Answer all questions MEDICAL PHYSIOLOGY EXAM ANSWERS MBMP 2300 - Section A: Short Answer Questions --- Question 1: How does the tubular secretion of H⁺ occur, and how does it achieve HCO₃⁻ reabsorption? (5 Marks) Answer: Tubular secretion of H⁺ occurs through two primary mechanisms: Primary Active Transport: H⁺-ATPase pumps in the apical membrane of intercalated cells actively transport H⁺ into the tubular lumen This process requires ATP and creates an electrochemical gradient Secondary Active Transport: Na⁺/H⁺ antiporter (exchanger) in proximal tubule cells exchanges intracellular H⁺ for luminal Na⁺ Driven by the sodium gradient maintained by basolateral Na⁺/K⁺-ATPase HCO₃⁻ Reabsorption Mechanism: Secreted H⁺ combines with filtered HCO₃⁻ in the lumen to form H₂CO₃ Carbonic anhydrase on the brush border converts H₂CO₃ to H₂O and CO₂ CO₂ diffuses into the cell and is converted back to HCO₃⁻ by intracellular carbonic anhydrase HCO₃⁻ exits the cell via basolateral Na⁺/HCO₃⁻ cotransporter, achieving net reabsorption --- Question 2: Discuss potassium secretion by the nephron. (5 Marks) Answer: Location and Mechanism: Primarily occurs in the principal cells of the collecting duct K⁺ enters cells via basolateral Na⁺/K⁺-ATPase pump K⁺ exits into tubular lumen through apical K⁺ channels (ROMK channels) Regulation: Aldosterone: Increases K⁺ secretion by:Increasing Na⁺/K⁺-ATPase activity Increasing apical K⁺ channel expression Enhancing Na⁺ reabsorption, creating favorable electrical gradient Plasma K⁺ concentration: High K⁺ levels directly stimulate aldosterone release and increase K⁺ secretion Tubular flow rate: Increased flow enhances K⁺ secretion by maintaining concentration gradients Acid-base status: Alkalosis promotes K⁺ secretion, while acidosis inhibits it Clinical Significance: Essential for K⁺ homeostasis and prevention of hyperkalemia Dysregulation can lead to dangerous cardiac arrhythmias --- Question 3: A male athlete taking large amounts of an androgenic steroid becomes sterile (unable to produce sperm capable of causing fertilization). Explain. (5 Marks) Answer: Mechanism of Steroid-Induced Infertility: Negative Feedback Suppression: Exogenous androgens suppress hypothalamic GnRH release This leads to decreased pituitary FSH and LH secretion Without adequate LH, Leydig cells reduce endogenous testosterone production Without adequate FSH, Sertoli cells cannot support spermatogenesis Direct Effects on Spermatogenesis: High concentrations of synthetic androgens may have direct toxic effects on developing sperm cells Altered testosterone/estrogen ratios affect normal sperm maturation Disruption of the blood-testis barrier function Testicular Atrophy: Prolonged suppression of gonadotropins leads to testicular shrinkage Reduced seminiferous tubule diameter and function Decreased sperm production and quality Reversibility: Effects are typically reversible but may take 6-12 months after cessation Some individuals may experience prolonged recovery or permanent damage --- Question 4: Describe the physiology of ejaculation. (5 Marks) Answer: Phases of Ejaculation: 1. Emission Phase: Triggered by sympathetic stimulation (T12-L2) Smooth muscle contraction of:Seminal vesicles Prostate gland Vas deferens Semen is deposited into the posterior urethra Internal urethral sphincter contracts to prevent retrograde ejaculation 2. Expulsion Phase: Controlled by parasympathetic and somatic nervous systems Rhythmic contractions of:Bulbospongiosus muscle Ischiocavernosus muscle Pelvic floor muscles External urethral sphincter relaxes Semen is forcefully expelled through the urethra Neural Control: Spinal ejaculatory center located at L1-L2 Requires integration of sympathetic, parasympathetic, and somatic pathways Coordinated by higher brain centers including the hypothalamus Refractory Period: Follows ejaculation Prevents immediate re-ejaculation Duration varies with age and individual factors --- Question 5: Where are thyroid hormone receptors located? How does thyroid hormone transduce its signal in the target cell? (5 Marks) Answer: Receptor Location: Nuclear receptors: Located in the cell nucleus bound to DNA Mitochondrial receptors: Present in mitochondria Cytoplasmic receptors: Some receptors exist in cytoplasm before nuclear translocation Plasma membrane receptors: Recently discovered membrane-bound receptors Signal Transduction Mechanism: Nuclear Pathway (Primary): T₃ (active form) enters the cell via membrane transporters T₃ binds to thyroid hormone receptors (TRα and TRβ) in the nucleus Receptor-hormone complex binds to thyroid response elements (TREs) on DNA Acts as transcription factor, increasing or decreasing gene expression Results in s