Ch 24 Digestive System - Lecture notes 14 PDF

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w/ Dr. Edith Ofuoku...

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Ch 24: Digestive System Monday, April 26, 2021

4:42 PM

I. Identify the Organs of the Digestive System, List Their Major Functions Describe the Histology of the Digestive Tract, and Outline the Mechanis Regulate Digestion A. General Digestive Functions 1. Ingestion: materials enter digestive tract via the mouth 2. Mechanical Processing: crushing & sheering makes materials ea propel along digestive tract 3. Digestion: the chemical breakdown of food into small organic fr for absorption by digestive epithelium 4. Secretion: release of water, acids, enzymes, buffers, and salts by glandular organs & epithelium of digestive tract 5. Absorption: movement of organic substrates, electrolytes, vitam water across digestive epithelium & into interstitial fluid of dige tract 6. Excretion: removal of waste products from body fluids B. Organs of the Digestive Systems 1. Oral Cavity, Teeth, Tongue - mechanical processing, moistenin with salivary secretions 2. Liver - secretion of bile (important for lipid digestion), storage o nutrients, and other vital functions 3. Gallbladder - storage and concentration of bile 4. Pancreas - exocrine cells secrete buffers and digestive enzymes, endocrine cells secrete hormones 5. Large Intestine - dehydration and compaction of indigestible m in preparation for elimination 6. Salivary Glands - secretion of lubricating fluid containing enzy break down carbohydrates 7. Pharynx - muscular propulsion of materials into the esophagus 8. Esophagus - transport of materials to the stomach 9 Stomach chemical breakdown of materials via acid and enzym

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9. Stomach - chemical breakdown of materials via acid and enzym mechanical processing though muscular contractions 10. Small Intestine - enzymatic digestion and absorption of water, substrates, vitamins, and ions II. Discuss the Anatomy of the Oral Cavity & List the Functions of its Majo Structures & Regions A. Major Anatomy of the Oral Cavity 1. Oral Mucosa a. Lining of cavity b. Extra thin and vascular under the tongue to rapidly absorb soluble drugs c. Cheeks supported by pads of fat and the buccinator muscle 2. Labia: lips 3. Vestibule: space between the cheeks/lips & teeth 4. Gingivae: gums a. Ridges of oral mucosa that surround base of each tooth 5. Tongue 6. Teeth B. Major Functions of Oral Cavity 1. Sensory analysis of materials before swallowing 2. Mechanical processing through teeth, tongue, and palatal surfac 3. Lubrication: mixing of substances with mucus and salivary glan secretions 4. Limited digestion of carbohydrates and lipids 5. Tongue a. Mechanical processing by compression, abrasion, and disto b. Manipulation to assist in chewing and prep for swallowing c. Sensory analysis by touch, temp, and taste receptors d. Secretion of mucins and the enzyme lingual lipase C. Accessory Anatomy and Functions 1. Salivary Glands: 3 pairs w/ distinct organization that produce different properties a. Submandibular produce 70% of saliva b. Parotids produce 25% c. Sublingual produce 5%

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2. Saliva a. 99.4% H2O b. 0.6% includes 1) Electrolytes (Na+ & Cl-) 2) Buffers 3) Glycoproteins (mucins) 4) Antibodies 5) Enzymes 6) Waste products c. Functions 1) Lubricate mouth & materials that enter 2) Dissolve chemicals that stimulate tastebuds & provid info 3) Salivary amylase: initiates digestion of complex carbs 3. Teeth a. masticate (chew) food b. Comprised of… 1) Dentin: mineral matrix that does not contain cells 2) Pulp cavity: receives blood vessels and nerves thru ro 3) Root: includes inferior pulp, surrounded by cementum 4) Crown: exposed portion that includes dentin and sup pulp covered by enamel c. Types of Teeth 1) Incisors: blade sharp in front of mouth for cutting 2) Cuspids (Canines): pointy on either side of mouth for 3) Bicuspids (Premolars): flat w/ prominent ridges that grind 4) Molars: same as premolars but w/ 3 roots III. Describe the Structure & Functions of the Pharynx IV. Describe the Structure & Functions of the Esophagus A. Esophagus Structure 1. Hollow and muscular 2. Begins posterior to cricoid cartilage 3. Wall of esophagus has 2 layers a. Mucosal

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b. Submucosal c. Muscularis B. Esophagus Function: conveys solid food and liquids to the stomach V. Describe the Anatomy of the Stomach, including its Histological Feature Discuss its Roles in Digestion & Absorption A. Anatomy of the Stomach 1. Shaped like thick J 2. Short lesser curvature - medial surface 3. Long greater curvature - lateral surface 4. Shape and size vary between individuals and daily meals 5. Regions - cardia, fundus, body, pylorus 6. Histology a. Simple columnar epithelium lines all portions 1) Produces mucus that covers interior surface of stomac 2) Gastric pits: shallow depressions that open onto gastr b. Gastric Glands 1) Fundus and body of stomach extend deep into underl lamina propria 2) Each gastric pit communicates w/ several gastric glan including parietal cells: secrete intrinsic factor and hydrochloric acid (HCl) & chief cells: secrete HCl and pepsinogen c. Pyloric glands in the pylorus that secrete mucous 7. Smooth muscle 8. Mucularis mucosae and mucularis externa contain extra layers smooth muscle cells in addition to circular and longitudinal lay B. Major Functions of the Stomach 1. Storage of ingested food 2. Mechanical breakdown pf ingested food 3. Disruption of chemical bonds in food material by acid and enzy 4. Production of intrinsic factor: glycoprotein required for absorpti vitamin B12 in small intestine

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C. Regulation of Gastric Activity 1. 3 phases a. Cephalic phase, gastric phase, and intestinal phase 2. Digestion and Absorption a. Preliminary digestion of proteins by pepsin b. Some digestion of carbs by salivary amylase c. Lipids by lingual lipase d. When digestion occurs stomach contents… 1) Become more fluid 2) pH approaches 2.0 3) Pepsin activity increases 4) Protein disassembly begins e. Digestion occurs in the stomach but nutrients are not abs here!! VI. Describe the Anatomical & Histological Characteristics of the Small Inte

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Explain the Functions & Regulation of Intestinal Secretions A. 90% of nutrients absorbed in small intestine!! B. Duodenum 1. Segment closest to stomach 2. "mixing bowl", receives chyme from stomach & secretions from and liver 3. Neutralizes acids before they can damage the absorptive surface small intestine C. Jejunum 1. Middle segment 2. Location of most chemical digestion & nutrient absorption 3. Few plicae circulares and small villi D. Ileum 1. Final segment 2. Ends at ileocecal valve: a sphincter that controls flow of materia the ileum into the large intestine E. Histology 1. Mucosa a. Inner lining b. Epithelium moistened by glandular secretions c. Lamina propria of areolar tissues 2. Submucosa a. Dense irregular CT b. Surrounds muscularis mucosae c. Blood and lymphatic vessels d. Exocrine glands that secrete buffers and enzyme into diges 3. Muscularis Mucosae a. Narrow band of smooth muscle and elastic fibers in lamina b. 2 layers 1) Circular muscle: inner layer that encircles lumen 2) Longitudinal layer: outer layer that contains muscle c parallel to tract 4. Serosa a. Serous membrane that covers muscularis externa b Not in the oral cavity pharynx esophagus and rectum

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b. Not in the oral cavity, pharynx, esophagus, and rectum VII. Describe the Structure, Functions, & Regulation of the Accessory Digest Organs A. Pancreas 1. Wrapped in thin CT capsule 2. Head - broad, by the loop of duodenum 3. Body - slender, extends toward spleen 4. Tail - short and rounded 5. Each lobule has ducts that branch repeatedly and end in blind p called pancreatic acini 6. Pancreatic islets - endocrine tissues of pancreas 7. Functions a. Endocrine cells secrete insulin and glucagon into bloodstre b. Exocrine cells = acinar cells and epithelial cells - secrete p juice that are controlled by hormones of duodenum and co pancreatic enzymes 8. Pancreatic Enzymes a. Pancreatic alpha-amylase breaks down starches b. Pancreatic lipase breaks down lipids c. Nucleases breaks down nucleic acids d. Proteolytic enzymes break down proteins B. Liver 1. Largest visceral organ 2. Anatomy a. Wrapped in fibrous capsule b. Divided into lobes 3. Hepatic blood supply a. 1/3 of blood supple from hepatic artery b. 2/3 from hepatic portal vein 4. Histology a. Lobules are basic functional units b. Six portal areas at each corner of lobule 1) Contain hepatic portal vein, branch of hepatic artery, small branch of bile duct 5. Functions Metab lic latio f

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a. Metabolic regulation of… 1) Composition of circulating blood 2) Nutrient metabolism 3) Waste product removal 4) Nutrient storage 5) Drug inactivation b. Metabolic activities 1) Carbohydrate metabolism 2) Lipid metabolism 3) Amino acid metabolism 4) Waste product removal 5) Vitamin storage 6) Drug inactivation c. Hematological Regulation 1) Largest blood reservoir in the body that receives 25% cardiac output 2) Functions of hematological regulation include… i. Phagocytosis and antigen presentation ii. Removal of circulating hormones, antibodies, an of toxins d. Synthesis and secretion of bile C. Bile Duct System 1. Liver secretes bile fluid into narrow channels called bile canalicu 2. Right and left hepatic ducts a. Collect bile from all bile ducts and form common hepatic d leaves liver 3. Bile flows from common hepatic duct to either common bile duc cystic duct 4. Common bile duct is form by joining of cystic duct and common duct 5. Functions of bile a. Mechanical processing of stomach creates large drops cont lipids b. Emulsification: Bile salts break droplets apart D. Gallbladder

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1. Stores and concentrates bile prior to excretion into small intestin 2. Regions a. Fundus - inferior b. Body - middle c. Neck - superior 3. Functions a. Stores bile b. Releases bile into duodenum under stimulation of hormon cholecystokinin (CCK) E. Intestinal Hormones 1. Secretin - increases secretion of bile 2. CCK - accelerates pancreatic production and secretion of digesti enzymes 3. GIP - secreted when fats and carbs enter small intestine 4. VIP - stimulates secretion of intestinal glands, inhibits acid prod 5. Gastrin - promotes increased stomach motility 6. Enterocrinin - stimulates mucin production in duodenum VIII. Describe the Gross Anatomy & Histological Structure of the Large Intes including its Regional Specializations & Role in the Nutrient Absorptio A. Anatomy 1. Cecum - pouchlike first portion a. Receives material arriving from ileum 2. Colon - the largest portion 3. Rectum - last part of digestive tract B. Appendix 1. Aka vermiform appendix 2. Lymphoid organ C. Colon 1. Ascending --> transverse --> descending --> sigmoid D. Functions 1. Less than 10% of nutrient absorption 2. Prepares fecal material for ejection from the body 3. Reabsorption of water and bile salts 4. Absorption of vitamins produced by bacteria and organic waste 5. Produces vitamin K, Biotin, and Pathogenic acid B5

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E. Elimination of Feces 1. Requires relaxation of internal and external anal sphincters 2. Reflexes open internal sphincter and close external sphincter 3. Opening external sphincter requires CNS IX. List the Nutrients Required by the Body, Describe the Chemical Events Responsible for the Digestion of Organic Nutrients, and Describe the Mechanisms Involved in the Absorption of Organic ad Inorganic Nutrie A. Essential Nutrients 1. Carbohydrates 2. Proteins 3. Lipids 4. Water 5. Electrolytes 6. Vitamins B. Digestion 1. Large organic molecules must be digested before absorption can 2. Water, electrolytes, and vitamins can be absorbed without proce may require special transport C. Processing & absorption of nutrients 1. Breaks down physical structure of food 2. Disassembles component molecules 3. Molecules released into bloodstream are absorbed by cells 4. Broken down to provide energy for ATP synthesis or used to sy carbs, proteins, and lipids X. Give Examples of Interactions Between the Digestive System & Other O Systems A. Integumentary System - provides vitamin D3 necessary for absorptio calcium and phosphorus B. Skeletal - teeth are used in mechanical processing of food C. Cardiovascular system - distributes hormones; carries nutrients, wat ions from sites of absorption; delivers nutrients and toxins to liver D. Respiratory System - respiratory muscles produce increased thoracic abdominal pressures that assist in defecation E. Muscular - controls entrances and exits of digestive tract F Nervous - hypothalamic centers control hunger satiation and feedin

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F. Nervous - hypothalamic centers control hunger, satiation, and feedin G. Endocrine - E & NE stimulate constriction of sphincters and depress cavity H. Lymphatic - lymphatic vessels carry absorbed lipids to general circul

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