END YEAR PP1 & PP2 2025 Physiology: MCQs for OmpathStudy

PAPER 2 --- MOUNT KENYA UNIVERSITY UNIVERSITY EXAMINATION 2024/2025 Medical School — Department of Physiology MBChB End of Year Examination — Year Two Unit: MBMP 1300 — Medical Physiology, Paper Two Date: Thursday 17th July, 2025 2:00 PM 2 Hours Instructions: Paper contains 2 sections: A and B Section A: Answer ALL questions Section B: Answer ANY 2 questions --- SECTION A — ANSWER ALL QUESTIONS--- 1. With examples, describe Phasic and Tonic gastrointestinal smooth muscle contractions. (5 Marks) Answer: Phasic contractions are rhythmic, intermittent contractions that occur and then relax in cycles. They are driven by slow waves and spike potentials. They are responsible for mixing and propelling food along the GI tract. Examples: peristalsis in the small intestine, segmentation contractions in the colon. Tonic contractions are sustained, continuous contractions that do not fully relax between contractions. They maintain constant muscle tone. Examples: the lower oesophageal sphincter (prevents reflux), the ileocaecal sphincter, and the internal anal sphincter — all of which must stay contracted at rest to control passage of contents. --- 2. Differentiate between ghrelin and leptin in the control of food intake. (5 Marks) Answer: Feature Ghrelin Leptin --- --- --- Source Stomach (fundus) Adipose tissue Effect on appetite Stimulates hunger (orexigenic) Suppresses hunger (anorexigenic) Timing Rises before meals; falls after eating Levels reflect long-term fat stores Target Hypothalamus (arcuate nucleus — stimulates NPY/AgRP) Hypothalamus (arcuate nucleus — stimulates POMC/CART) Response to fasting Increases Decreases Response to obesity Often low or normal High, but receptor resistance develops In summary: ghrelin tells the brain to eat; leptin tells the brain to stop eating and that energy stores are sufficient. --- 3. Explain how carbohydrates are absorbed in the small intestine. (5 Marks) Answer: Dietary carbohydrates are first broken down by salivary and pancreatic amylase into oligosaccharides and disaccharides (maltose, sucrose, lactose). Brush border enzymes (maltase, sucrase, lactase) on the luminal surface of enterocytes then hydrolyse these into monosaccharides (glucose, galactose, fructose). Absorption occurs as follows: Glucose and galactose are absorbed via SGLT1 (sodium-glucose cotransporter) — secondary active transport, coupled to sodium entry down its gradient Fructose is absorbed via GLUT5 — facilitated diffusion (passive, no energy required) All three monosaccharides exit the enterocyte on the basolateral side via GLUT2 into the portal circulation, travelling to the liver --- 4. Discuss the effect of stress on the endocrine system via the hypothalamus-pituitary-adrenal (HPA) axis. (5 Marks) Answer: When a stressor is perceived, the hypothalamus releases Corticotropin-Releasing Hormone (CRH) . CRH travels via the hypothalamo-hypophyseal portal system to the anterior pituitary, stimulating release of ACTH (adrenocorticotropic hormone) . ACTH enters the systemic circulation and acts on the zona fasciculata of the adrenal cortex, stimulating synthesis and release of cortisol . Cortisol's effects during stress: Raises blood glucose (gluconeogenesis, glycogenolysis) Mobilises fatty acids from adipose tissue Suppresses immune and inflammatory responses Maintains vascular tone and cardiac output Negative feedback: Cortisol feeds back to both the hypothalamus and anterior pituitary to suppress further CRH and ACTH release, preventing excessive cortisol production. Chronic stress overwhelms this feedback, leading to prolonged elevated cortisol with harmful effects (immunosuppression, hypertension, muscle wasting, impaired wound healing). --- 5. Explain why someone with a parathyroid gland tumour might develop kidney stones. (5 Marks) Answer: A parathyroid tumour (adenoma) causes primary hyperparathyroidism — autonomous, unregulated excess secretion of PTH . PTH normally: Increases bone resorption (osteoclast activity) → releases Ca²+ and PO₄³⁻ into blood Increases renal calcium reabsorption in the distal tubule Increases renal phosphate excretion Stimulates vitamin D activation → increases intestinal calcium absorption With a tumour, PTH is produced in excess regardless of calcium levels, causing hypercalcaemia . When plasma calcium exceeds the renal threshold, excess calcium is filtered and excreted in urine ( hypercalciuria ). In the renal tubules and collecting system, calcium combines with oxalate, phosphate, or other anions to precipitate as calcium-containing kidney stones (nephrolithiasis). --- 6. Describe the ovarian and endometrial changes during the luteal phase of the menstrual cycle. (5 Marks) Answer: Ovarian changes: After ovulation (around day 14), the ruptured follicle is transformed under the influence of LH into the corpus luteum . The granulosa and theca cells luteinise, becoming large, lipid-filled luteal cells. The corpus luteum secretes large amounts of progesterone and moderate amo