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The Digestive System

The Digestive System. Functions to break down food substances into forms that can be absorbed. Types of Digestion. Mechanical Chemical. Digestive Processes. Ingestion Digestion Absorption Elimination. Divisions of the Digestive System. Gastrointestinal tract

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The Digestive System

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  1. The Digestive System Functions to break down food substances into forms that can be absorbed

  2. Types of Digestion • Mechanical • Chemical

  3. Digestive Processes • Ingestion • Digestion • Absorption • Elimination

  4. Divisions of the Digestive System • Gastrointestinal tract • Oral cavity, pharynx, esophagus, stomach, large and small intestines • Accessory structures • Teeth, tongue, salivary glands, liver, pancreas, and gallbladder

  5. Layers of the GI Tract • Mucosa - innermost layer • Epithelium - stratified squamous (pharynx and esophagus) and simple columnar • Lamina propria - areolar connective tissue • Muscularis - smooth muscle layer causing small folds

  6. Layers of GI Tract • Submucosa - loose connective tissue containing blood vessels, nerves, glands, and lymphatics • Muscularis - two layers of smooth muscle • inner circular layer and outer longitudinal one • some skeletal muscle

  7. Serosa - outer mesothelium • Peritoneum (parietal and visceral) • Extensions: mesentery, mesocolon, greater and lesser omentum, falciform ligament

  8. Organs and Structures

  9. Mouth • Vestibule • Tongue • Teeth • Salivary glands

  10. Mouth or Buccal Cavity • Vestibule- area bounded by the lips and cheeks externally/internally by the gums and teeth • Tongue - striated skeletal muscle that manipulates food, help form words, and serves as a sense organ • Teeth - breaks food into smaller pieces increasing surface area for digestion

  11. Teeth • Found in alveolar sockets • Primary (deciduous or baby) teeth • Usually consists of 20 teeth) • Permanent teeth (32 teeth) • Incisors - chisel-shaped • Canines (Cuspids) - fang-like • Premolars (bicuspids) - grinding and crushing • Molars - grinding and crushing

  12. Tooth Structure • Crown - exposed portion above gum • Covered in enamel • Dentin - fills interior of tooth • Neck - hidden by gumline • Root - embedded in jawbone, number of roots varies • Cementum - attaches tooth to periodontal ligament

  13. Salivary Glands • Parotid glands • Submandibular glands • Sublingual glands • Functions: • cleanses, dissolves, moistens, digests • 97% water • Slightly acidic • Contains electrolytes, salivary amylase, mucin, lysozymes, and immunoglobulins

  14. Esophagus • Hollow muscular tube that functions to carry food to the stomach through an opening in the diaphragm called the esophageal hiatus • Upper third composed of skeletal musle; lower regions made of smooth muscle • Hiatal hernia

  15. Digestive Processes of the mouth, pharynx, & esophagus • Mastication - chewing • Deglutition - swallowing • chewed food formed into bolus • tongue blocks mouth, soft palate blocks nasopharynx, epiglottis blocks trachea • Peristalsis - rhythmic contractions of circular muscles causing food to move down GI tract

  16. Stomach • Serves as a reservoir for food and to mix food with gastric juice • Regions: cardia, fundus, body, and pylorus • Greater and lesser curvatures • Pyloric sphincter • Rugae • Additional oblique smooth muscle layer

  17. Gastric gland cells • Mucous goblet cells - secrete mucosal layer • Parietal cells (oxyntic) - secrete HCl and intrinsic factor • Chief cells (zymogenic) - secrete pepsinogen • Pepsinogen converted to pepsin which breaks proteins into peptides • Enteroendocrine cells (G-cells)- secrete hormones: • gastrin, histamine, endorphins, serotonin, cholecystokinin, somatostatin • Stomach ulcers - caused by Heliobacter pylori

  18. Digestive Processes in the Stomach • Mechanical & chemical digestion turns food into chyme • Pepsin breaks down proteins into peptides • Rennin (in children) breaks down milk • Intrinsic factor - required for absorption of vitamin B12 in the intestines

  19. Gastric motility & emptying • Stomach contractions produce chyme, increase mixing of food • Entire stomach can hold up to 4L • Approx. 3 ml squirts through pylorus with each contraction • Stomach contracts 3X/min • Usually empties within 4 hours but may be delayed depending on contents

  20. Pancreas • Secretes pancreatic juice formed by acini • Pancreatic juice • sodium bicarbonate that serves to buffer HCl • proteases such as trypsin, chymotrypsin, and carboxypeptidase • pancreatic amylase • pancreatic lipases • pancreatic nucleases

  21. Liver and Gallbladder • Largest internal organ in the body • Consists of right and left lobe separated by the falciform ligament; caudate and quadrate lobes on the posterior surface • Digestive function includes the production of bile; protein, carbohydrate & lipid metabolism; removal of drugs & hormones • Gallbladder - stores and concentrates bile

  22. Small Intestines Duodenum, Jejunum, and Ileum

  23. Small Intestine • Duodenum - (10 inches) receives chyme from the stomach and digestive secretions from the pancreas and liver ; major digestion occurring here • Secretin • Cholecystokinin (CCK) • Gastric inhibitory peptide (GIP)

  24. Jejunum and Ileum • 8 + 12 = 20 feet long • Region where most absorption occurs • Plica circulares = folds • Villi lined with simple columnar epithelium • Each villus contains an arteriole, venule, capillary bed and a lacteal • Microvilli form brush border • Peristalsis and segmentation occurs

  25. Enzymes of the small intestine • Dextrinase break down • Glucoamylase oligosaccharides • Maltase break • Sucrase down • Lactase disaccharides • Carboxypeptidase breaks • Aminopeptidase down • Dipeptidase proteins

  26. Large Intestine • 5.5 feet long • Functions: • reabsorption of remaining water and electrolytes • absorption of vitamins B and K (produced by the bacterial flora) • elimination of feces (may take 12-24 hours)

  27. Large Intestine • Cecum • Ileocecal valve • Appendix • Ascending, transverse, and descending colon • Sigmoid colon • Taeniae coli / Haustra • Rectum / Anus • Hemorrhoids/Diverticulitis

  28. Products of Digestion • Carbohydrates • Lipids • Proteins

  29. Carbohydrates • Monosaccharides - single sugars • Glucose • Fructose • Galactose • Deoxyribose • Ribose

  30. Carbohydrates • Disaccharides - double sugars • Sucrose • Lactose • Maltose • Polysaccharides - starches (many sugars) • Amylose • Cellulose • Glycogen

  31. Formation of a disaccharide +

  32. Formation of a fat

  33. Carbohydrate Digestion • Carbohydrates are broken down into disaccharides and then into monosaccharides • Starch (Amylose)+ amylase --> Maltose • Maltose + Maltase --> 2 Glucose molecules • Lactose + Lactase --> Galactose & Glucose • Sucrose + Sucrase --> Glucose & Fructose

  34. Lipid Digestion • Lipids (fats) + Lipase ---> Glycerol & Fatty Acids • This process is made more efficient by the emulsifying action of bile.

  35. Protein Digestion • Protein + Pepsin --> large polypeptides • Protein + Rennin --> large polypeptides • Protein + Trypsin --> small polypeptides • Protein + Chymotrypsin --> small polypeptides • Protein + Carboxypeptidase --> sm. Plypeptds • Aminopeptidases - to single amino acids • Carboxypeptidase - to single amino acids • Dipeptidase - to single amino acids

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