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The Digestive System

The Digestive System. Organ groups of digestion. Alimentary organs Mouth Pharynx Esophagus Stomach Small and large intestine Accessory digestive organs Teeth and tongue Liver Pancreas Salivary glands gallbladder. The processes of digestion. Ingestion Secretion

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The Digestive System

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  1. The Digestive System

  2. Organ groups of digestion • Alimentary organs • Mouth • Pharynx • Esophagus • Stomach • Small and large intestine • Accessory digestive organs • Teeth and tongue • Liver • Pancreas • Salivary glands • gallbladder

  3. The processes of digestion • Ingestion • Secretion • Mixing and propulsion • Mechanical and chemical digestion • Absorption • Defecation

  4. Peristalsis and segmentation • Peristalsis

  5. Layers of the GI tract • Mucosa • Layer of epithelium • Lamina propria (connective tissue) • Thin layer of smooth muscle (muscularis mucosae) • Submucosa • Muscularis • Serosa

  6. ANS input • Vagus nerve supplies parasympathetic input to most parts of the GI tract. • Preganglionic parasympathetic neurons synapse on postsynaptic neurons in the submucosal and myenteric plexuses. • Parasympathetic stimulation increases motility and GI secretion. • Sympathetic postsynaptic neurons in the plexuses decrease GI section and decrease motility by inhibiting neurons of ENS

  7. Mouth • Buccal cavity • Oral mucosa • Vestibule • Gingivae • Hardpalate • Soft palate • Uvula

  8. Salivary glands • Cleanse mouth • Dissolve food chemicals • Moisten food • Enzymes break down carbs

  9. Teeth • Crown, neck and root • Peridontal ligament • Enamel • Dentin • Root canal

  10. Tooth varieties • Incisors • Cuspids • Bicuspids • Molars • Mastication • Bolus

  11. Tongue

  12. Swallowing • Deglutition • 3 phases • Buccal • Pharyngeal • Esophogeal • Peristalsis • Secondary peristaltic waves

  13. Deglutition

  14. Stomach • Fundus • Body • Pylorus • Pyloric sphincter • Rugae

  15. Stomach histology

  16. Gastric Glands • Mucous cells • Surface & neck • G cells • Parietal cells • Chief cells • Enteroendocrine cells

  17. Stomach and chemical digestion Cephalic (Reflex) phase • Triggered by sensory signals surrounding food. • Activates vagal nerve and ANS to enhance secretions • Hydrochloric Acid Production in Parietal Cells

  18. Stomach and chemical digestion Gastric Phase • Activation of local myeteric reflexes and vagovagal reflexes • Gastrin • Release of HCl from parietal cells

  19. Stomach and chemical digestion • Intestinal Phase • Excitatory component • Inhibitory component

  20. Gastric Secretion: 3 Phases

  21. Stomach and mechanical digestion • Stomach filling • Contractile activity • Peristalsis • Gastric emptying

  22. Small intestine and associated organs

  23. Small intestine histology

  24. Small intestine histology

  25. Liver • Digestive function is to produce bile. • Metabolic function is to process venous blood from digestive tract • Functional unit is a lobule

  26. Liver

  27. Liver Functions • Carbohydrate metabolism • Lipid metabolism • Protein metabolism • Processing of drugs and hormones • Excretion of bilirubin • Synthesis of bile salts • Storage • Phagocytosis • Activation of vitamin D

  28. Cholesterol

  29. Accessory organs

  30. Bile • Alkaline solution that includes bile salts, phospholipids and electrolytes. • Bile salts derived from cholesterol • Bile salts emulsify fats and solubilize cholesterol, increasing absorption. • Bile is recycled • Fatty chyme and bile returning to liver stimulates more production of bile.

  31. Gallbladder • The gallbladder stores and concentrates bile. • Bile release into duodenum • Fatty chyme stimulates release of CKK and secretin. • CKK enters bloodstream • Bile salts and secretin in the blood stimulate liver to rapidly produce bile. • Vagal stimulation leads to weak contractions. • CKK causes gallbladder to contract and the hepatopancreatic sphincter to relax; bile enters duodenum

  32. Pancreatic juice • Insulin & Glucose Regulation

  33. Digestion in Small intestine: chemical • Digestion of carbohydrates • Pancreatic amylase • Brush-border enzymes • Digestion of proteins • Enzymes from pancreatic juice • Brush-border peptidases releases single AAs • Digestion of lipids • Digestion & Absorption of Fats • Digestion of nucleic acids

  34. Digestion in Small intestine: mechanical • Segmentation leads to chyme being moved backwards and forwards. • Parasympathetic input increases intensity of contractions; sympathetic input decreases intensity. • Peristalsis occurs after nutrients are absorbed; regulated by motilin. • Migrating motility complex • Movement through ileocecal sphincter is enhanced by gastrin. • Once meal has passed through sphincter back pressure keeps the valve closed

  35. Water • Water moves in both directions and follows flow of electrolyhtes

  36. Large intestine (5 ft) • Mechanical digestion—haustral churning, peristalsis, mass peristalsis • Chemical digestion • Absorption • Feces formation • Reflexes in the Colon

  37. Ulcerative Colitis

  38. Defecation reflex • Mass peristaltic movements • Voluntary contractions of diaphragm and abdominals • Parasympathetic input • Voluntary input

  39. Resources • Human Digestion • Heart Burn Video • Peristalsis Animation • Digestive System

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