General & Systemic Pathology SAQ Paper II — OmpathStudy

General & Systemic Pathology SAQ Paper II — 15 July 2025 (MBPA 3500, MKU Year 3) Mount Kenya University, School of Medicine, Department of Pathology. Bachelor of Medicine and Bachelor of Surgery — Year 3. Unit Code: MBPA 3500 — Unit Title: General & Systemic Pathology SAQ, Paper II. Main Exam, 15th July 2025, 2:30 PM. Time: 3 Hours. This exam consists of two sections: Section A — 10 short answer questions (10 marks each, attempt all); Section B — three long essay questions (20 marks each, attempt all). Model answers below are written for revision; they are not an official marking scheme. SECTION A — SHORT ANSWER QUESTIONS Attempt all. Each question carries 10 marks. --- Question 1 Give an outline of the various congenital neural tube defects, mentioning their distinguishing features. (10 Marks) Answer: Anencephaly — failure of closure of the rostral (cranial) neuropore; absence of the cranial vault, scalp and most of the brain (only a rudimentary brainstem/area cerebrovasculosa remains); incompatible with life, frequently associated with polyhydramnios (absent fetal swallowing reflex). Spina bifida occulta — failure of fusion of the vertebral arches only, with an intact overlying skin and no herniation of neural tissue; often an incidental finding, sometimes marked by a skin dimple, hairy patch or lipoma over the lumbosacral spine. Meningocele — herniation of the meninges (dura and arachnoid) through a vertebral defect, forming a fluid-filled sac covered by skin; the spinal cord itself remains in its normal position, so neurological deficit is uncommon. Myelomeningocele — herniation of both meninges and neural tissue (spinal cord/nerve roots) through the vertebral defect; the most common and most severe open form, usually associated with significant motor/sensory deficit below the lesion and with hydrocephalus (Arnold-Chiari II malformation). Encephalocele — herniation of meninges (± brain tissue) through a cranial defect, most often occipital. All are caused by failure of neural tube closure between the 3rd and 4th week of gestation; folate deficiency is a major modifiable risk factor, hence periconceptional folic acid supplementation for prevention. --- Question 2 Classify chemical carcinogenic agents giving examples of each class and the cancers they are associated with. (10 Marks) Answer: Chemical carcinogens are classified as direct-acting (require no metabolic conversion) and indirect-acting/procarcinogens (require metabolic activation, usually hepatic cytochrome P450, to become the active "ultimate carcinogen"). Direct-acting agents: alkylating agents (e.g. cyclophosphamide, busulfan) — associated with treatment-related acute myeloid leukaemia. Polycyclic aromatic hydrocarbons (indirect-acting): benzo[a]pyrene and other products of tobacco smoke, smoked/charred food, and fossil fuel combustion — associated with lung, laryngeal and bladder cancer. Aromatic amines/azo dyes (indirect-acting): e.g. beta-naphthylamine, benzidine (rubber/dye industry exposure) — associated with transitional cell (urothelial) carcinoma of the bladder. Nitrosamines: formed endogenously from nitrites/nitrates in preserved and smoked foods — associated with gastric and oesophageal carcinoma. Aflatoxin B1 (from Aspergillus flavus on stored grains/groundnuts): associated with hepatocellular carcinoma, especially synergistic with chronic Hepatitis B infection. Asbestos: associated with malignant mesothelioma and bronchogenic carcinoma. Vinyl chloride: associated with hepatic angiosarcoma. Arsenic: associated with skin and lung cancer. Benzene: associated with acute myeloid leukaemia. --- Question 3 Compare and contrast autosomal dominant and autosomal recessive disorders focusing on their mode of transmission and the manifestation of their clinical features. (10 Marks) Answer: Feature Autosomal Dominant Autosomal Recessive --- --- --- Gene dose required One mutant allele (heterozygous) is sufficient Two mutant alleles (homozygous, or compound heterozygous) required Transmission pattern Vertical — affects successive generations; affected individual has ~50% risk of transmitting to each child Horizontal — typically skips generations; both parents are usually unaffected carriers; ~25% of offspring of two carriers affected Sex ratio Equal in males and females Equal in males and females Parental consanguinity Not typically relevant Increases risk, since it raises the chance both parents share the same rare recessive allele Onset/severity Often later onset; clinical expression can be milder because one normal allele is still present Usually earlier and more uniform/severe onset, since no normal gene product is produced Variability of expression Marked — shows variable expressivity (severity differs between affected individuals) and incomplete penetrance (some gene carriers show no phenotype at all) Expression tends to be more uniform/complete penetrance within a family, since the biochemical defect is total loss of function Typical mec