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The Digestive System

Honors Anatomy & Physiology. The Digestive System. Gastrointestinal (GI) tract . AKA alimentary canal or gut Continuous muscular digestive tube Mouth Pharynx Esophagus Stomach Small intestine Large intestine A nus. Digestive Processes. Ingestion Taking food in Propulsion

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The Digestive System

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  1. Honors Anatomy & Physiology The Digestive System

  2. Gastrointestinal (GI) tract • AKA alimentary canal or gut • Continuous muscular digestive tube • Mouth • Pharynx • Esophagus • Stomach • Small intestine • Large intestine • Anus

  3. Digestive Processes • Ingestion • Taking food in • Propulsion • Swallowing -voluntary • Peristalsis – waves of involuntary contractions (see fig a) • Mechanical Digestion • Chewing, mixing w/saliva by tongue, churning food in stomach • Segmentation – constriction of intestines mixes food w/juices (see fig b) • Chemical Digestion • Catabolic break down by enzymes • Absorption • Chemical building blocks, vitamins, minerals, and water from lumen of GI into blood & lymph • Defecation • Eliminates indigestibles

  4. The Mouth AKA Buccal or Oral cavity • Lines w/stratified squamous epithelium • Labia (lips) – orbicularisoris (poorly keratinized) • Cheeks – buccinators for chewing • Hard Palate – rigid surface for tongue to mash food • Soft palate – skeletal muscle w/ uvula • Tongue- skeletal muscle fibers in various directions, repositions food and mixes w/saliva to form bolus lingual frenulum attaches to floor

  5. Salivary Glands • 1,000 – 1,500 mL per day! • Regulated by parasympathetic division of ANS • Functions: • Cleanses mouth • Dissolves food chemicals for taste • Moistens food to compact into bolus • Amylase breaks down starch • Composition • 97% water, electrolytes • pH 6.75 • Amylase, mucin (forms mucus), lingual lipase • Antimicrobials: lysozyme, IgA, defensins • Multiple Locations: • Extrinsic salivary glands • Intrinsic salivary glands – continuous secretion • Buccalgalnds • Paratid gland • Submandibular gland • Sublingual gland

  6. Teeth • Function: Masticate (Chew) voluntary & reflexive • 20 Primary (deciduous) or milk teeth by 24 months • Roots reabsorbed as adult teeth develop causing them to fall out between 6-12 yrs • 32 Permanent teeth (including wisdom teeth) • Types: • Incisors - cutting • Canines – tear/pierce • Premolars (bicuspids) – grinding & crushing • Molars (4-5 cusps) • Structure: • Enamel – acellular hardest substance in body (Ca and hydroxyapatite), cannot be replaced • Gingiva recedes w/age • Dentin – bonelike but avascular • Cementum – Ca connective tissue covers root • Peridontalliagment anchors to alveolus

  7. Pharynx • Oropharynx & laryngopharynx • Stratified squamous epithelium w/mucus producing glands • 2 skeletal muscle layers: • inner layer longitudinal • Constrictor muscles encircle • Peristalsis propels food into esophagus

  8. Esophagus • Collapsed 10” muscular tube • Pierces diaphragm to join to cardiac sphincter of stomach • Takes 2 (liquids) -8 (solids) seconds • 4 layers: • Nonkeratinized stratified squamous epithelium • Longitudinal folds when empty, flatten when food is in transit • Esophageal glands – secrete mucus as bolus moves thru • Skeletal & smooth muscle

  9. Stomach • Storage tank where bolus + enzymes = chyme • 6-10” long, ‘J’ shaped • Mechanical digestion • Vigorous peristalsis • Chemical digestion • HCl denatures proteins • Chief cells secrete pepsin & lipase • rennin (milk proteins) • Absorption • Alcohol & aspirin (lipid soluble) pass through stomach mucosa into blood (can cause gastric bleeding) • Secretes intrinsic factor to absorb vitamin B12 in small intestine • Mucus barrier Rugae – fold when empty Omentum –mesenteries that tether digestive organs to body wall (fat & lymph)

  10. Small Intestine • 20 ft long, 1.5” diameter, complete trip about 2 hours • Simple columnar epithelium w/goblet cells and T cells • Intestinal crypts w/defensins & lysozyme & stem cells • 2 layers of muscle for segmentation • Peyer’s patches • Huge SA for absorption • Villi – 1mm fingerlike projections w/capillary bed & lacteal (lymph) • Microvilli – brush border projections of plasma membrane w/ bound enzymes to complete carb & protein digestion • 3 subdivisions: • Duodenum - 10” curves around pancreas • Bile duct • Pancreatic duct • Duodenal glands produce bicarbonate mucus to neutralize acidic chyme • Jejunum – 8’ long • Ileum – 12’ long

  11. Liver & Gallbladder • Liver • Largest gland in body (3lbs), 4 primary lobes • Produces 500-1,000 mL bile/day – fat emulsifier • Gallbladder • 4” long, inferior surface of right lobe • Store bile (yellow-green alkaline solution) • Salts, pigments (bilirubin), cholesterol, triglycerides, phospholipids & electrolytes

  12. Pancreas • Pancreatic juice (1200-1500mL/day) released via pancreatic duct which fuses w/bile duct as enters duodenum • Acini – clusters of secretory cells • Pancreatic proteases: trypsin, carboxypeptidase, chymotrypsin • Amylase, lipases, nucleases • Islets of Langerhans • βcells secrete – insulin (↓ blood glucose) • αcells secrete – glucagon ( blood glucose) • Bicarbonate ions – pH 8

  13. Large Intestine • 7cm diameter, 1.5 meters • Function: reabsorb remaining water from indigestible food residue & eliminate as feces • 12-24 hours to reclaim water & electrolytes • Simple columnar epithelium • Deep crypts w/goblet cells to ease passage of feces • Mass movements: slow powerful contractive waves, fiber increases strength contractions • Subdivisions: • Cecum - pouch • Appendix – lymph tissue • Colon – ascending, transverse, descending and sigmoid • Rectum – has valves to separate feces from flatus! • Anal Canal – 2 sphincters (1 involuntary & 1 voluntary), stratified squamous epithelium

  14. Bacteria Flora • Over 700 species! • Survivors from small intestine or enter via anus • Ferment indigestible carbs (cellulose, xylan) • Metabolize proteins (mucin, heparin, hyaluronic acid) • Release 500mL gasses/day (H2, N2, CH4, CO2, and smelly dimethyl sulfide) • Synthesize vitamin B & K • Lymph cells moniter to ensure they do not stray

  15. Physiology of Chemical Digestion • Catabolic process: polymers hydrolyzed monomers • Complete Enzyme Chart: • Carbs: Amylase, dextrinase, glucoamylase, maltase, sucrase, lactase • Proteins:Pepsin, trypsin, chymotrypsin, carboxypeptidase, aminopeptidase, dipeptidase • Lipids: bile, lipase • Nucleic Acids: ribonuclease, deoxyribonuclease, phosphatases

  16. Development of Digestive System • Endoderm forms lining GI tract • Rest develops from mesoderm

  17. Nutrition • Nutrients – promote growth, maintenance & repair • Carbohydrates • Glucose oxidized to ATP (mitochondria) • Energy measured in kilocalories or Calories (heat energy required to raise 1kg of water 1OC) • RDA: 130g digestible, 25-30g of fiber • Lipids • Utilized for phospholipids, myelin, insulation, cushion, stored energy, steroid hormones, absorb fat-soluble vitamins • RDA: 80-100g plant/animal fats; <250mg cholesterol • Proteins • Structural uses: keratin, collagen, elastin, muscle proteins, etc • Functional uses: enzymes, hormones, pigments, and transport • Can be oxidized for energy in liver • RDA: 0.8%g/kg of body weight • Vitamins • Organic compounds function as coenzymes • Classified as fat or water soluble • Minerals • Inorganic • Ionized or bound to organic compounds • Water

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