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The Digestive System Chapter 23 – Lecture Notes

The Digestive System Chapter 23 – Lecture Notes. to accompany Anatomy and Physiology: From Science to Life textbook by Gail Jenkins, Christopher Kemnitz, Gerard Tortora. Chapter Overview. 23.1 Gastrointestinal (GI) Tract 23.2 Accessory Organs of the Head 23.3 Swallowing 23.4 Stomach

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The Digestive System Chapter 23 – Lecture Notes

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  1. The Digestive SystemChapter 23 – Lecture Notes to accompany Anatomy and Physiology: From Science to Life textbook by Gail Jenkins, Christopher Kemnitz, Gerard Tortora

  2. Chapter Overview 23.1 Gastrointestinal (GI) Tract 23.2 Accessory Organs of the Head 23.3 Swallowing 23.4 Stomach 23.5 Accessory Organs of the Abdomen 23.6 Small Intestine 23.7 Large Intestine 23.8 Phases of Digestion 23.9 Food Molecules 23.10 Metabolism

  3. Essential Terms digestion • process of mechanically or chemically breaking down food absorption • passage of small molecules into blood and lymph digestive system • organs which carry out process of digestion and absorption metabolism • all the chemical reactions of the body

  4. Introduction Digestive System • Composed of GI tract and accessory organs • Breaks down ingested food for use by the body • Digestion occurs by mechanical and chemical mechanisms • Excretes waste products or feces through process of defecation

  5. Concept 23.1Gastrointestinal (GI) Tract

  6. GI Tract / Alimentary Canal • Continuous tube from mouth to anus • Mouth • Pharynx • Esophagus • Stomach • Small intestine • Large intestine

  7. Accessory Digestive Organs • Provide mechanical and chemical mechanisms to aid digestion • Teeth • Tongue • Salivary glands • Liver • Gallbladder • Pancreas

  8. Figure 23.1

  9. Functions of Digestive System • Ingestion • Secretion • Mixing and propulsion • Motility • Digestion • Mechanical and chemical • Absorption • Defecation

  10. Layers of GI Tract • Same in all areas of GI tract • From deep to superficial: • Mucosa • Submucosa • Muscularis • Serosa

  11. Figure 23.2

  12. Layers of GI Tract • Mucosa • Epithelium • Type varies • Lamina propria – areolar connective tissue • MALT – mucus-associated lymphatic tissue • Muscularis mucosae – smooth muscle • Submucosa • Areolar connective tissue • Blood and lymphatic vessels • Neurons – submucosal plexus

  13. Layers of GI Tract • Muscularis • Skeletal and smooth muscle • Neurons – myenteric plexus • Serosa • Areolar and simple squamous epithelium • Visceral peritoneum

  14. Peritoneum • Mesothelium • Parietal peritoneum • Visceral peritoneum • Peritoneal cavity • Retroperitoneal

  15. Figure 23.3a

  16. Figure 23.3b

  17. Figure 23.3c

  18. Figure 23.3d

  19. Folds of Peritoneum • Greater omentum • Adipose tissue • Falciform ligament • Liver to anterior abdominal wall • Lesser omentum • Mesentery • Small intestine to posterior abdominal wall • Mesocolon

  20. Neural Innervation of GI Tract • Regulated by autonomic nervous system • Enteric division • Myenteric plexus / plexus of Auerbach • Submucosal plexus / plexus of Meissner • Able to function independently from rest of nervous system • Linked to CNS by extrinsic sympathetic and parasympathetic nerves • Sympathetic nerves decrease GI secretions & motility • Parasympathetic nerves increase GI secretion and motility

  21. Concept 23.2Accessory Organs of the Head

  22. Mouth Parts of Digestive System • Mouth formed by several parts: • Cheeks • Lips / labia • Labial frenulum • Orbicularis • Vestibule • Oral cavity proper • Fauces • Hard and soft palate • Uvula • Palatoglossal and palatopharyngeal arch

  23. Figure 23.4

  24. Tongue • Skeletal muscle and mucous membrane • Helps form floor of oral cavity • Extrinsic muscles • Intrinsic muscles • Lingual frenulum • Papillae • Fungiform • Filiform • Circumvallate • Foliate • Lingual glands • Lingual lipase

  25. Salivary Glands • Release saliva to oral cavity • 3 pairs of salivary glands • Parotid • Submandibular • Sublingual

  26. Composition of Saliva • 99.5 % water • 0.5% other solutes • Ions • Mucus • Immunoglobulin A • Enzymes • Salivation controlled by autonomic nervous system • Stimulated by various mechanisms

  27. Figure 23.5

  28. Teeth • External regions • Crown • Root • Neck • Internal components • Enamel • Dentin • Cementum • Pulp cavity • PulpRoot canals • Apical foramen

  29. Figure 23.6

  30. Teeth • Dentitions • Deciduous teeth – first set • Permanent teeth – secondary • Carry out mechanical digestion by mastication • Creates bolus • Salivary amylase • Breakdown starch • Lingual lipase • Breakdown triglycerides

  31. Figure 23.7

  32. Table 23.1

  33. Concept 23.3Swallowing

  34. Pharynx • Composed of skeletal muscle • Lined by mucous membrane • Nasopharynx • Oropharynx • Laryngopharynx

  35. Esophagus • Collapsible muscular tube through esophageal hiatus of diaphragm • Mucosa • Submucosa contains areolar connective tissue • Muscularis • Skeletal muscle • Upper and lower esophageal sphincter • Adventitia • Attaches esophagus to nearby structures • Secrets mucus and transports food

  36. Figure 23.8

  37. Deglutition • Stages of swallowing • Voluntary • Mouth to oropharynx • Pharyngeal • Deglutition center in medulla oblongata and pons • Closing of epiglottis • Involuntary • Esophageal • Involuntary • Peristaltic contractions

  38. Figure 23.9a,b

  39. Figure 23.9c

  40. Table 23.2

  41. Concept 23.4Stomach

  42. Stomach • Serves as mixing chamber and storage area for ingested food • Rugae allow for increased volume • 4 main regions • Cardia • Fundus • Body • Pylorus • Pyloric antrum and canal • Pyloric sphincter • Lesser and greater curvatures

  43. Figure 23.10a

  44. Stomach Histology • Mucosa • Surface mucous cells • Lamina propria • Muscularis mucosae • Gastric glands and pits • Parietal cells • Chief cells • G cells • Submucosa – areolar connective tissue • Muscularis • 3 layers of smooth muscle • Serosa

  45. Figure 23.11a

  46. Figure 23.11b

  47. Figure 23.11c

  48. Mechanical and Chemical Digestion • Mixing waves caused by peristaltic movement • Chyme released in process of gastric emptying • Proton pumps bring H+ into the lumen • Carbonic anhydrase forms carbonic acid to provide H+ and bicarbonate ions (HCO3-)

  49. Figure 23.12

  50. Mechanical and Chemical Digestion • Chemical digestion stimulated by nervous system • Parasympathetic neurons release acetylcholine • Works with gastrin • HCl released in presence of histamine • Pepsin begins digestion of proteins • Stomach protected by alkaline mucus secretion • Gastric lipase digests triglycerides • Few molecules absorbed by stomach • Water, ions, short-chain fatty acids, alcohol

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