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The Digestive System
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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