Medical Physiology II Essays OmpathStudy

GOOD LUCK DAKTARI END SEMESTER CAT MONDAY, 24TH MARCH 2025 SECTION B: ASSAY (ANSWER ALL) --- SECTION B: ESSAY QUESTIONS 1. i. Describe the different sensations from the urinary bladder at different urine volumes. (5 MARKS) The urinary bladder exhibits distinct sensations as it fills, mediated by stretch receptors and neural pathways: 0–150 mL: No noticeable sensation – the bladder is in the filling phase , and stretch receptors are inactive. 150–300 mL: First awareness of bladder filling – slight stretch activates low-threshold mechanoreceptors , but no urgency to void. 300–400 mL: Moderate urge to urinate – afferent signals via pelvic nerves (S2–S4) trigger the micturition reflex , but voluntary control can suppress it. 400–600 mL: Strong urge to void – high-threshold stretch receptors fire, causing discomfort. The detrusor muscle contracts involuntarily if the reflex is not inhibited. 600 mL: Pain and risk of overdistension – excessive stretching can impair bladder function, leading to urinary retention or detrusor muscle damage . --- 1. ii. Describe the countercurrent multiplier by the nephron. (5 MARKS) The countercurrent multiplier establishes a medullary osmotic gradient, crucial for water reabsorption: Descending Limb (Permeable to Water, Impermeable to Solutes): Water exits passively into the hypertonic medulla → tubular fluid becomes more concentrated . Ascending Limb (Impermeable to Water, Actively Transports Solutes): Na+, Cl−, K+ actively pumped out via NKCC2 transporters → interstitial osmolarity increases. Tubular fluid becomes hypotonic as solutes are removed. Vasa Recta (Countercurrent Exchanger): Maintains the gradient by removing reabsorbed water and solutes without disrupting the gradient. Result: A hypertonic medulla (1200 mOsm/L) allows the collecting duct to reabsorb water under ADH control , concentrating urine. --- 2. Describe the micturition reflex. (10 MARKS) The micturition reflex is a spinal cord-mediated process controlled by autonomic and somatic nerves: 1. Filling Phase (Sympathetic Dominance, T11–L2): Detrusor muscle relaxation via β₃-adrenergic receptors . Internal urethral sphincter contraction (α₁-receptors). 2. Reflex Activation (300–400 mL, Parasympathetic, S2–S4): Stretch receptors in the bladder wall send afferent signals via pelvic nerves . Spinal reflex activates parasympathetic efferents → detrusor contraction and internal sphincter relaxation . 3. Voluntary Control (Pudendal Nerve, S2–S4): External urethral sphincter (skeletal muscle) remains contracted until voluntary relaxation. Pontine micturition center integrates signals, allowing conscious voiding. 4. Voiding Phase: Detrusor contracts , sphincters relax → urine expulsion. In infants , the reflex is purely spinal; adults have cortical inhibition. --- 3. i. Describe the hormonal regulation of the menstrual cycle and the associated changes in the ovary and uterus. (10 MARKS) 1. Follicular Phase (Days 1–14): FSH stimulates follicle growth → granulosa cells secrete estrogen . Estrogen thickens the endometrium (proliferative phase) . Negative feedback on FSH → dominant follicle selected. 2. Ovulation (Day 14): LH surge (triggered by high estrogen ) → follicle rupture (ovulation). 3. Luteal Phase (Days 15–28): Corpus luteum forms → secretes progesterone and estrogen . Progesterone induces secretory endometrium (glandular development). If no fertilization : Corpus luteum degenerates → progesterone drops → menstruation . --- 3. ii. Explain the process of sexual differentiation in humans. (5 MARKS) Genetic Sex (XX or XY): SRY gene on Y chromosome → testis development (Leydig & Sertoli cells). No SRY → ovary development . Hormonal Control: Testes secrete: Testosterone → Wolffian ducts → male structures (epididymis, vas deferens). AMH (Anti-Müllerian Hormone) → regresses Müllerian ducts . Ovaries (No testosterone/AMH) → Müllerian ducts form fallopian tubes, uterus. External Genitalia: DHT (from testosterone) → penis & scrotum . Absence of androgens → clitoris, labia, vagina . --- SECTION B: ESSAY QUESTIONS 1. Role of Intestinal Disaccharidases in Carbohydrate Digestion (10 MARKS) Key Points: Disaccharidases are brush-border enzymes that break down disaccharides into monosaccharides for absorption. Pancreatic amylase initiates starch digestion but cannot break α(1→6) bonds (handled by isomaltase ). Lactase deficiency causes lactose intolerance (undigested lactose → osmotic diarrhea). --- 2. Zymogens in Protein Digestion (10 MARKS) Key Points: Enteropeptidase (duodenal brush border) is the master activator (converts trypsinogen → trypsin). Trypsin then activates other pancreatic zymogens. Pepsin works optimally at low pH (stomach), while pancreatic enzymes require alkaline pH (HCO₃⁻ from pancreas). --- 3. i. Absorption of Lipid Digestion Products (5 MARKS) Micelle Formation: Bile salts emulsify fats → form mixed micelles with fatty acids (FA), monoglycerides, cholesterol. Micelles deliver lipids to enterocyte brush border.