Human Physiology IV: Main Exam, 14 November 2022
Mount Kenya University · Department of Dental Sciences · Diploma in Community Oral Health · DMP2104
Human Physiology IV past paper from Mount Kenya University 2022-2023 with model answers for salivary glands, pancreatic juice, bile, taste, HCl and more.
Instructions: ATTEMPT ALL QUESTIONS IN SECTIONS A AND B.
Section A (30 marks)
1.
- a)
- i) Write short notes on major salivary glands in the oral cavity. (5 marks)
- ii) State the functions of saliva in the oral cavity. (5 marks)
Model answer- Parotid gland: largest, located near ear; serous secretion rich in amylase; drains via Stensen’s duct.
- Submandibular gland: beneath mandible; mixed serous‑mucous secretion; drains via Wharton’s duct.
- Sublingual gland: under the tongue; predominantly mucous secretion; drains via multiple ducts (Rivinus).
- Serous acini: produce watery enzyme‑rich fluid.
- Mucous acini: produce viscous mucus for lubrication.
- Functions of saliva:
- Lubrication of oral tissues and bolus formation.
- Digestion: amylase initiates starch breakdown; lipase begins fat digestion.
- Protection: antimicrobial enzymes (lysozyme, peroxidase) and IgA.
- Buffering: bicarbonate neutralises acids, protecting teeth.
- Taste: dissolves substances, enabling taste receptor activation.
- b) Explain the functions pancreatic juice. (6 marks)Model answer
- Digestive enzyme delivery: pancreatic amylase, lipase and proteases (trypsin, chymotrypsin) break down carbohydrates, fats and proteins in the duodenum.
- Neutralisation of gastric acid: bicarbonate raises pH, protecting intestinal mucosa and optimising enzyme activity.
- Activation of enzymes: enteropeptidase converts trypsinogen to trypsin, initiating the proteolytic cascade.
- Facilitation of nutrient absorption: breakdown products (maltose, fatty acids, amino acids) become ready for transport across the intestinal wall.
- Lubrication: fluid component eases chyme movement through the small intestine.
- Regulation: hormones (secretin, CCK) modulate pancreatic secretion according to luminal contents.
- c) Highlight two (2) fundamentally important functions of bile. (4 marks)Model answer
- Emulsification of fats: bile salts break large fat globules into smaller droplets, increasing surface area for lipase.
- Facilitation of fat absorption: bile salts form micelles that solubilise fatty acids and monoglycerides for transport to the intestinal mucosa.
- d) What can affect the sense of taste? (6 marks)Model answer
- Age: reduced taste bud density and nerve function in the elderly.
- Medications: antihypertensives, antibiotics, chemotherapeutic agents can alter taste perception.
- Oral health: infections, dental disease, xerostomia diminish taste.
- Nutritional deficiencies: zinc, vitamin B12 deficits impair taste buds.
- Neurological disorders: stroke, Parkinson’s disease affect gustatory pathways.
- Smoking and alcohol: chronic exposure desensitises taste receptors.
- e) State the composition of saliva (4 marks)Model answer
- Water (≈99% of saliva).
- Electrolytes: sodium, potassium, calcium, magnesium, chloride, bicarbonate.
- Proteins/enzymes: amylase, lipase, lysozyme, peroxidase, lactoferrin.
- Mucins: high‑molecular‑weight glycoproteins providing viscosity.
Section B (40 marks)
2. Discuss salivary components and their functions (20 marks)
Model answer
- Amylase: initiates starch digestion into maltose and dextrins.
- Lipase (lingual): begins triglyceride hydrolysis, especially in infants.
- Lysozyme: antibacterial enzyme that cleaves bacterial cell walls.
- Lactoferrin: binds iron, inhibiting bacterial growth.
- Immunoglobulin A (IgA): provides immune defence on mucosal surfaces.
- Mucins: glycoproteins that lubricate, protect epithelium and form the mucous pellicle.
- Growth factors (EGF, NGF): promote oral mucosal healing and cell turnover.
- Buffering agents (bicarbonate, phosphate): maintain pH, protect teeth from acid attack.
- Antioxidants (uric acid, glutathione): neutralise free radicals in the oral cavity.
- Electrolytes: regulate osmotic balance and facilitate nerve impulse transmission.
- Proline‑rich proteins: bind tannins, reducing astringency of foods.
- Histatins: antimicrobial peptides with antifungal activity against Candida.
- Statherin: inhibits calcium phosphate precipitation, maintaining tooth enamel integrity.
- Cystatins: protease inhibitors that protect oral tissues.
- Enzymes for tissue remodeling (matrix metalloproteinases): aid in wound healing.
- Nitric oxide synthase substrates: contribute to local vasodilation and defence.
- pH regulators: maintain optimal environment for enzyme activity.
- Taste‑modulating proteins: influence perception of bitter and sweet compounds.
- Antimicrobial peptides (defensins): broad‑spectrum defence against oral pathogens.
- Salivary flow regulators (e.g., vasoactive intestinal peptide): control secretion rate.
3. Explain the roles of Hydrochloric Acid (HCl) in the stomach (20 marks)
Model answer
- Activates pepsinogen: Converts pepsinogen to active pepsin, the primary proteolytic enzyme.
- Denatures dietary proteins: Unfolds protein structures, exposing peptide bonds to enzymatic cleavage.
- Provides optimal pH for pepsin: Maintains gastric lumen at pH 1‑3, the range where pepsin activity is maximal.
- Kills ingested microorganisms: Creates an acidic environment that destroys many bacteria, viruses and parasites.
- Facilitates mineral absorption: Solubilises calcium, iron and magnesium salts, enhancing their later absorption in the intestine.
- Stimulates gastric mucosal growth: Low pH triggers release of gastrin, which promotes mucosal cell proliferation.
- Regulates gastric emptying: Acidic chyme slows gastric emptying, allowing adequate time for digestion.
- Activates intrinsic factor: Acidic conditions are required for proper folding of intrinsic factor, essential for vitamin B12 absorption.
- Inhibits gastric pathogens: Suppresses overgrowth of Helicobacter pylori and other acid‑sensitive microbes.
- Promotes secretion of bicarbonate: Triggers duodenal Brunner’s gland bicarbonate release to neutralise acid entering the small intestine.
- Aids in lipid emulsification: Acidic pH assists bile salt micelle formation when chyme mixes with bile in the duodenum.
- Enhances drug dissolution: Improves solubility of certain oral medications (e.g., aspirin) for better absorption.
- Provides feedback for acid secretion: Low pH stimulates somatostatin release, which negatively regulates further HCl production.
- Protects oral cavity: Acidic gastric contents reduce oral bacterial load when reflux occurs (though chronic reflux is harmful).
- Supports gastric mucosal barrier: Acid stimulates mucus and bicarbonate secretion that coat the epithelium.
- Facilitates gastric hormone release: Low pH triggers gastrin release from G‑cells, reinforcing acid secretion.
- Assists in protein coagulation: Causes denaturation and coagulation of proteins, forming a protective curd that slows nutrient absorption.
- Prepares chyme for pancreatic enzymes: Acidic environment ensures optimal pH shift when neutralised, allowing pancreatic enzymes to function efficiently.
- Contributes to taste perception: Acidic environment stimulates taste buds for sour taste, influencing appetite and food intake.
- More answers: modulation of gut microbiota composition, activation of certain zymogens besides pepsin, and involvement in signaling pathways that regulate appetite.