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Digestive System

Digestive System. Ch 23. What is the function of the digestive system?. Provide the body w/nutrients, water and electrolytes. The organs of this system are responsible for: Food ingestion Digestion Absorption Elimination

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Digestive System

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  1. Digestive System Ch 23

  2. What is the function of the digestive system? • Provide the body w/nutrients, water and electrolytes. • The organs of this system are responsible for: • Food ingestion • Digestion • Absorption • Elimination • The digestive system consists of a hollow tube extending from the mouth to the anus (GI tract or alimentary canal). • Various accessory organs empty secretions into them.

  3. Digestive Process • Ingestion • Propulsion • Mechanical Digestion • Mastication • Churning food in stomach • Chemical digestion • Absorption • Defecation

  4. GI Tract- 4 basic tunics: • Mucosa • Submucosa • Muscularis externa • Serosa (adventia)

  5. GI Tract (alimentary canal) • 1. Mucosa- wet epithelial membrane • Major function: • secretion • absorption • protection • reduce friction • protect cells from being digested • 2. Submucosa- moderately dense connective tissue • Contains: • blood • lymphatic vessels • scattered lymph nodules and nerve fibers • Major function: • nutrition • protection

  6. 3. Muscularis externa- bilayer of smooth muscle and superficial longitudinal muscle • Major function: • regulate GI motility (churning) • 4.Serosa- serous membrane • Major function: • reduce friction • anchor and protect the surrounding GI tract organ

  7. Enteric Nervous System (Autonomic & Somatic Connections) Parasympathetic Nerve Innervation of the GI Tract Enteric Nervous System To ANS & CNS neurons Myenteric Plexus Submucosal Plexus motor motor sensory Mucosal Muscularis

  8. Teeth Incisors Incisors Central (7 yr) Central (6–8 mo) Lateral (8 yr) Lateral (8–10 mo) Canine (eyetooth) (11 yr) Canine (eyetooth) (16–20 mo) Premolars (bicuspids) Molars First molar (10–15 mo) First premolar (11 yr) Deciduous (milk) teeth Second molar (about 2 yr) Second premolar (12–13 yr) Molars First molar (6–7 yr) Second molar (12–13 yr) Third molar (wisdom tooth) (17–25 yr) Permanent teeth (a) Figure 23.10a

  9. Teeth (b) Deciduous teeth Permanent teeth Figure 23.10b

  10. incisors Teeth cuspid premolars molars

  11. Salivary Glands Extrinsic salivary glands • Parotid • Submandibular • Sublingual

  12. Salivary Glands Parotid gland • Anterior to the ear external to the masseter muscle • Parotid duct opens into the vestibule next to second upper molar Submandibular gland • Medial to the body of the mandible • Duct opens at the base of the lingual frenulum

  13. Salivary Glands Sublingual gland • Anterior to the submandibular gland under the tongue • Opens via 10–12 ducts into the floor of the mouth

  14. Salivary Glands Secretion (saliva) • Cleanses the mouth • Moistens and dissolves food chemicals • Aids in bolus formation • Contains enzymes that begin the breakdown of starch

  15. Saliva • Water (99.5%) • mucin • Amylase and lingual lipase • Electrolytes- Na+, K+, Cl–, PO4 2–, HCO3 • Glycoproteins • antibacterial compounds such as secretory IgA and lysozyme

  16. Salivary Glands

  17. Tongue Functions include • Repositioning and mixing food during chewing • Formation of the bolus • Initiation of swallowing, speech, and taste • Intrinsic muscles change the shape of the tongue • Extrinsic muscles alter the tongue’s position • Lingual frenulum: attachment to the floor of the mouth

  18. Tongue Surface bears papillae • Filiform—whitish, give the tongue roughness and provide friction • Fungiform—reddish, scattered over the tongue • Circumvallate (vallate)—V-shaped row in back of tongue • These three house taste buds • Foliate—on the lateral aspects of the posterior tongue

  19. Epiglottis Palatine tonsil Lingual tonsil Foliate papillae Circumvallate papilla Fungiform papilla Filiform papilla Figure 23.8

  20. Peristalsis

  21. Peristalsis

  22. Deglutition (swallowing)

  23. Peristalsis Waves

  24. Stomach Lining Gastric pits Surface epithelium (mucous cells) Gastric pit Mucous neck cells Parietal cell Gastric gland Chief cell Enteroendocrine cell (b) Enlarged view of gastric pits and gastric glands

  25. Stomach Secretions • Gastric Pit: • hydrochloric acid • pepsinogen • Mucus • Hormones that regulate GI motility

  26. Mucous neck cells- found in upper region of gastric glands • produce • mucous • Parietal cells- in gastric gland of mucosa • produce • HCl – kills most bacteria • Intrinsic factor (required for absorption of vit. B12 in sm intestine, which is needed for producing mature erythrocytes) • Zymogenic (chief) cells- • produce • pepsinogen • (inactive form of pepsin, which becomes active in presence of HCl) • rennin • (milk digestion in children)  protein digestion

  27. Enteroendocrine cells in stomach mucosa • produces: • Gastrin- regulates stomach secretions and mobility • Histamine- activates parietal cells to release HCl • Endorphins- natural opiates • Serotonin- causes contraction of stomach muscle • Cholecystokinin (CCK)- (in duodenal mucosa) many functions and affects many organs • Somatostatin- (stomach and duodenal mucosa) - inhibits gastrin, pancreatic secretions, inhibits GI blood flow in sm intestine…

  28. Gastric ulcers • erosion of stomach wall; pain occurs 1-3 hrs after eating • 90% of recurrent ulcers due to bacterial infection, which destroys mucous protective barrier; • Treatment- use antibiotic therapy to kill bacteria Helicobacter pylori Barry Marshal

  29. Bile • Bile salts • Bile pigments • Cholesterol • Neutral fats • Phospholipids • Other electrolytes

  30. Bile secretion

  31. Small Intestine, Gallbladder, & Pancreas

  32. Pancreas Endocrine function • Pancreatic islets secrete insulin and glucagon Exocrine function • Acini (clusters of secretory cells) secrete pancreatic juice • Zymogen granules of secretory cells contain digestive enzymes

  33. Small duct Acinar cells Basement membrane Zymogen granules Rough endoplasmic reticulum (a) Figure 23.26a

  34. Pancreatic Juice • Watery alkaline solution (pH 8) neutralizes chyme • Electrolytes (primarily HCO3–) • Enzymes • Amylase, lipases, nucleases are secreted in active form but require ions or bile for optimal activity • Proteases secreted in inactive form

  35. Pancreatic Juice Protease activation in duodenum • Trypsinogen is activated to trypsin by brush border enzyme enteropeptidase • Procarboxypeptidase and chymotrypsinogen are activated by trypsin

  36. Pancreatic Enzymes • trypsin • chemotrypsin • carboxypeptidase • amylase • phospholipase • lipase • nucleases

  37. Small Intestine: Gross Anatomy • Major organ of digestion and absorption • 2–4 m long; from pyloric sphincter to ileocecal valve • Subdivisions • Duodenum (retroperitoneal) • Jejunum (attached posteriorly by mesentery) • Ileum (attached posteriorly by mesentery)

  38. Intestinal Structure muscle layers lumen folds villi

  39. Small Intestine

  40. Intestinal Villus epithelial cells capillaries lacteal

  41. Intestinal Epithelial Cell

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