--- UNIT CODE : MBMP 2300 UNIT TITLE : Medical Physiology DATE : Thursday, 13th July 2023 TIME : 8:00 AM – 10:00 AM DURATION : 2 Hours --- INSTRUCTIONS - This
--- UNIT CODE : MBMP 2300 UNIT TITLE : Medical Physiology DATE : Thursday, 13th July 2023 TIME : 8:00 AM – 10:00 AM DURATION : 2 Hours --- INSTRUCTIONS - This paper consists of two sections: A and B . - Attempt all questions in Section A and any two (2) questions from Section B. - The use of mobile phones or any form of exam irregularity is strictly prohibited . --- SECTION A – SHORT ANSWER QUESTIONS (60 Marks) PHYSIOLOGY EXAM ANSWERS - SECTION A Short Answer Questions (60 Marks) 1. Three types of nerve fibers with examples (5 marks) A Fibers (Myelinated, Large Diameter) - Aα fibers : Motor neurons to skeletal muscle, proprioceptive fibers from muscle spindles (12-20 μm diameter, 70-120 m/s conduction velocity) - Aβ fibers : Touch, pressure, vibration sensory fibers (5-12 μm diameter, 30-70 m/s conduction velocity) - Aγ fibers : Motor neurons to muscle spindle intrafusal fibers (3-6 μm diameter, 15-30 m/s conduction velocity) - Aδ fibers : Sharp pain, cold temperature, some touch sensory fibers (2-5 μm diameter, 12-30 m/s conduction velocity) B Fibers (Lightly Myelinated, Medium Diameter) - Preganglionic autonomic fibers (both sympathetic and parasympathetic) - 1-3 μm diameter, 3-15 m/s conduction velocity C Fibers (Unmyelinated, Small Diameter) - Postganglionic sympathetic fibers - Dull, aching pain sensory fibers - Warm temperature sensory fibers - Some visceral sensory fibers - 0.4-1.2 μm diameter, 0.5-2 m/s conduction velocity --- 2. Emmetropia and four types of refractive errors (5 marks) Emmetropia is the normal refractive state of the eye where parallel light rays from distant objects ( 6 meters) focus exactly on the retina without accommodation. The eye has perfect optical power matching its axial length. Four Types of Refractive Errors: A. Myopia (Nearsightedness) - Light rays focus in front of the retina - Caused by: Excessive axial length of eyeball or excessive refractive power - Symptoms: Distant objects appear blurred, near objects clear - Correction: Concave (diverging) lenses B. Hyperopia (Farsightedness) - Light rays focus behind the retina - Caused by: Insufficient axial length of eyeball or insufficient refractive power - Symptoms: Near objects appear blurred (accommodation strain), distant objects may be clear - Correction: Convex (converging) lenses C. Astigmatism - Irregular curvature of cornea or lens causing different refractive powers in different meridians - Light rays do not focus at a single point - Symptoms: Blurred vision at all distances, eye strain, headaches - Correction: Cylindrical lenses to correct the meridian with abnormal curvature D. Presbyopia - Age-related loss of lens elasticity and accommodation ability - Begins around age 40-45 years - Symptoms: Difficulty focusing on near objects, need to hold reading material farther away - Correction: Convex lenses for near vision, bifocals, or progressive lenses --- 3. Physiological events during REM sleep (5 marks) Neurological Events: - Rapid eye movements (horizontal, vertical, and oblique) - Vivid, complex dreaming with emotional content - Increased brain activity similar to waking state - Activation of visual, motor, and limbic areas - Suppression of norepinephrine, serotonin, and histamine release Motor System Changes: - Muscle atonia (paralysis of voluntary muscles except diaphragm and extraocular muscles) - Inhibition of spinal motor neurons via glycine and GABA - Occasional muscle twitches despite atonia - Preserved respiratory muscle function Autonomic Changes: - Fluctuations in heart rate and blood pressure - Irregular breathing patterns - Loss of thermoregulation (poikilothermic state) - Increased oxygen consumption and metabolic rate - Penile erections in males/clitoral engorgement in females Hormonal Changes: - Decreased growth hormone release - Reduced cortisol secretion - Suppressed antidiuretic hormone (ADH) release --- 4. Decussation and its significance in the pyramidal motor system (5 marks) Definition of Decussation: Decussation refers to the crossing over of nerve fibers from one side of the nervous system to the other, forming an X-shaped intersection. Pyramidal System Decussation: - Occurs at the pyramidal decussation (decussation of pyramids) in the medulla oblongata - 85-90% of pyramidal tract fibers cross to the opposite side - Forms the lateral corticospinal tract - 10-15% remain uncrossed, forming the anterior corticospinal tract Significance: A. Contralateral Motor Control - Left cerebral hemisphere controls right side of body and vice versa - Explains why unilateral brain lesions cause motor deficits on the opposite side B. Clinical Implications - Stroke in left motor cortex causes right-sided hemiplegia - Upper motor neuron lesions above decussation cause contralateral symptoms - Lower motor neuron lesions below decussation cause ipsilateral symptoms C. Evolutionary Advantage - Allows for better integration of sensory input and motor output - Facilitates coordinated bilateral movements - Enables specialization of cerebral hemispheres --- 5. Functions of Cholecystokinin (CCK) (5 marks) Digestive Functions: - Gallbladder contraction : Stimulates powerful contraction and bile release - Pancreatic enzyme secretion : Stimulates release of digestive enzymes (lipase, amylase, proteases) - Sphincter of Oddi relaxation : Allows bile and pancreatic juice to enter duodenum - Gastric emptying inhibition : Slows gastric motility to allow proper digestion Appetite and Satiety: - Satiety hormone : Reduces food intake by signaling fullness to the brain - Vagal stimulation : Activates vagal afferents that communicate with hypothalamus - Meal termination : Helps end eating behavior through central nervous system effects Neural Functions: - Neurotransmitter in CNS : Functions as neuropeptide in brain and spinal cord - Anxiolytic effects : May have anti-anxiety properties - Memory and learning : Involved in hippocampal function Regulatory Functions: - Insulin release : Stimulates insulin secretion from pancreatic beta cells - Growth regulation : Promotes pancreatic growth and enzyme synthesis - Motility coordination : Coordinates digestive tract motility patterns --- 6. Paracrine and neurocrine secretions of the GI system (5 marks) Paracrine Secretions (Local cell-to-cell communication): A. Somatostatin - Source: D cells in stomach, duodenum, and pancreatic islets - Functions: Inhibits gastric acid secretion, gastrin release, insulin and glucagon secretion B. Histamine - Source: Enterochromaffin-like (ECL) cells in gastric mucosa - Functions: Stimulates gastric acid secretion from parietal cells C. Prostaglandins (PGE2, PGI2) - Source: Various GI mucosal cells - Functions: Inhibit gastric acid secretion, stimulate mucus and bicarbonate production, protect gastric mucosa D. Nitric Oxide (NO) - Source: Enteric neurons and endothelial cells - Functions: Smooth muscle relaxation, vasodilation, inhibits gastric acid secretion Neurocrine Secretions (Neural communication): A. Acetylcholine (ACh) - Source: Parasympathetic (vagal) nerve terminals and enteric neurons - Functions: Stimulates gastric acid secretion, increases GI motility, stimulates enzyme secretion B. Norepinephrine - Source: Sympathetic nerve terminals - Functions: Inhibits GI motility, reduces blood flow to GI tract, inhibits secretions C. Vasoactive Intestinal Peptide (VIP) - Source: Enteric neurons - Functions: Smooth muscle relaxation, stimulates intestinal secretion, inhibits gastric acid secretion D. Gastrin-Releasing Peptide (GRP/Bombesin) - Source: Enteric neurons - Functions: Stimulates gastrin release from G cells --- 7. Process of saliva formation (5 marks) Primary Secretion (Acinar Cells): - Isotonic plasma-like fluid : Initial secretion similar to plasma in electrolyte composition - Protein secretion : α-amylase, mucins, lysozyme, lactoferrin, and other proteins - Cholinergic stimulation : Parasympathetic stimulation increases protein-rich secretion - Adrenergic stimulation : Sympathet