Gastrointestinal Pathology Exam: H. pylori, OmpathStudy

MOUNT KENYA UNIVERSITY — MEDICAL SCHOOL Programme: Bachelor of Medicine and Bachelor of Surgery, Year 3 Assessment: Mid of Semester 2 — Continuous Assessment Test (CAT) Unit Code: MBPA 3515 — Gastrointestinal System Pathology Date: February 2026 Time: 30 minutes --- Question 1: "List the congenital anomalies found in the gastrointestinal tract." (10 marks) Answer: Atresia (e.g., esophageal atresia, duodenal atresia, anal atresia) — complete luminal obstruction Stenosis — partial luminal narrowing (e.g., pyloric stenosis) Tracheoesophageal fistula — abnormal connection between trachea and esophagus Meckel's diverticulum — persistent vitelline (omphalomesenteric) duct remnant Malrotation of the gut — abnormal intestinal rotation during development Omphalocele — herniation of abdominal contents into the umbilical cord, covered by peritoneum Gastroschisis — herniation of abdominal contents through an abdominal wall defect, without a covering sac Hirschsprung disease (congenital aganglionic megacolon) — absence of ganglion cells in the distal bowel Duplication cysts — congenital duplication of segments of the GI tract Diaphragmatic hernia — abnormal opening allowing abdominal organs into the thoracic cavity Imperforate anus --- Question 2: "List the unique macroscopic and microscopic morphological features of the following diagnoses:" a) Boerhaave syndrome (1 mark) Spontaneous transmural (full-thickness) rupture of the esophagus, classically at the distal left posterolateral wall, typically due to a sudden rise in intraesophageal pressure (e.g., forceful vomiting) b) Barrett oesophagus (3 marks) Macroscopic: Salmon-pink, velvety mucosa replacing the normal pale, glossy squamous esophageal mucosa, typically extending upward from the gastroesophageal junction Microscopic: Intestinal metaplasia — normal stratified squamous epithelium replaced by columnar epithelium containing goblet cells Clinical significance: Represents a precursor lesion with increased risk of progression to esophageal adenocarcinoma via a dysplasia-carcinoma sequence --- Question 3: "Give a brief outline of the virulence factors linked to the pathogenesis of chronic gastritis implicated in Helicobacter pylori." (8 marks) Answer: Urease: hydrolyses urea to ammonia, neutralising local gastric acid and creating a protective microenvironment around the bacterium, while also being directly toxic to epithelial cells Flagella: enable motility, allowing the bacterium to move through the mucus layer to reach the epithelial surface Adhesins (e.g., BabA): mediate adherence to gastric epithelial cells, preventing clearance and facilitating colonisation CagA (cytotoxin-associated gene A): injected into host cells via a type IV secretion system, disrupts cell signalling, promotes inflammation, and is strongly associated with increased virulence and cancer risk VacA (vacuolating cytotoxin A): induces epithelial cell vacuolation, apoptosis, and disrupts tight junctions, increasing mucosal permeability Proteases and phospholipases: break down the protective mucus layer, weakening the mucosal barrier LPS (lipopolysaccharide): triggers host innate immune/inflammatory response, contributing to chronic mucosal inflammation Immune evasion mechanisms: H. pylori alters its surface antigens and modulates host immune responses, allowing it to persist and cause chronic (rather than self-limiting) infection --- Question 4: "Briefly outline four (4) different mechanisms through which intestinal obstruction occurs." (8 marks) Answer: Volvulus/torsion: twisting of a loop of bowel around its mesenteric attachment, causing luminal occlusion and compromising blood supply Intussusception: telescoping of one segment of bowel into an adjacent distal segment, causing mechanical obstruction and risk of ischaemia Adhesions: fibrous bands (often post-surgical or post-inflammatory) that kink or compress the bowel externally, causing obstruction Functional obstruction (ileus): failure of normal peristalsis (e.g., paralytic ileus) without a true mechanical blockage, often due to disturbed neuromuscular coordination (Additional acceptable mechanisms from your notes): Hirschsprung disease: congenital absence of ganglion cells in the distal colon causes failure of relaxation and functional obstruction Luminal/faecal obstruction: blockage of the bowel lumen by a mass such as impacted faeces, gallstones, or foreign bodies