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Gross anatomy and histology of the alimentary system

Gross anatomy and histology of the alimentary system. Lecture 21 Monday, February 26, 2007 Refs. Ross and Pawlina Chapter 17, Wheater’s Chapter 14 and Moore and Dalley Chapter 2. Alimentary system.

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Gross anatomy and histology of the alimentary system

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  1. Gross anatomy and histology of the alimentary system Lecture 21 Monday, February 26, 2007 Refs. Ross and Pawlina Chapter 17, Wheater’s Chapter 14 and Moore and Dalley Chapter 2

  2. Alimentary system • Definition: The organs associated with ingestion and digestion of food including the mouth, pharynx, digestive tube, and associated organs and glands. • Teeth, tongue, salivary glands, liver, pancreas, gall bladder • Esophagus, stomach, duodenum, jejunum, ileum, large intestine, rectum, and anus (hollow viscera or gut) • Other terms:Digestive system, gastrointestinal (GI) system

  3. Functions of the alimentary system • Ingestion of food and water • deglutition (swallowing), bolus, saliva • Fragmentation of food • Mastication, stomach, result is chyme • Digestion • Saliva, stomach (pepsin), small intestine (pancreatic enzymes and bile) • Absorption • Small intestine (nutrients), large intestine (mainly water) • Elimination of waste

  4. Generalized histology of alimentary tract WFH 14.1

  5. Layers of the digestive tract • Mucosa • Epithelium • Lamina propria-supporting connective tissue, MALT • Muscularis mucosae-thin layer of smooth muscle • Submucosa • Connective tissue, larger vessels, nerves • Tunica muscularis or muscularis propria • Usually 2 layers-circular inner, longitudinal outer layer • Adventitia or serosa • Connective tissue± mesothelium

  6. Wall of the GI tract (longitudinal section of esophagus) at low magnification WFH 14.3b

  7. Enteric nervous system • Modulates peristalsis and secretory activity • ± Autonomic nervous system • Independent local reflex activity • Diffuse • Components • Postganglionic sympathetic fibers • Ganglia of parasympathetic nervous system • Postganglionic parasympathetic fibers • Plexus = a network • Submucosal = Meissner’s • Myenteric = Auerbach’s

  8. Muscularis mucosae and submucosa with parasympathetic ganglia (large intestine) WFH 14.3a

  9. Parasympathetic ganglia (myenteric plexus) between circular and longitudinal layers of muscularis propria WFH 14.3c

  10. Transverse section of esophagus at low magnification shows folded mucosa, MALT, submucosal glands (connective tissue stained blue) WFH 14.4a

  11. Gross anatomy of the stomach WFH 14.6

  12. Abrupt change in epithelium from stratified squamous to glandular at gastro-esophageal junction WFH 14.5

  13. Schematic of glands of the body and fundus of the stomach WFH 14.8

  14. Gastric or oxyntic glands • Secrete gastric juice (pH 0.9-1.5) • Parietal cells secrete acid and intrinsic factor. • Chief cells secrete pepsinogen. • Surface and pits are lined by mucous cells. • Secrete mucus and bicarbonate ions. • Up to 7 glands open into pit at isthmus. • Stem cells are in the neck of gland- daughter cells migrate up or down the gland as they differentiate.

  15. Gastric mucosa of body. Gastric pits take up about one fourth the length of gland WFH 14.9

  16. Base of gastric gland: chief cells have basophilic basal cytoplasm; parietal cells have centrally located nucleus and eosinophilic cytoplasm WFH 14.10

  17. Chief cell:extensive RER and apical zymogen granules WFH 14.11

  18. Parietal cell: abundant mitochondria and canaliculiWFH 14.12

  19. Pyloric glands have deep pits and secrete mucus. Neuroendocrine cells secreting gastrin shown by immunostaining. WFH 14.13c

  20. Gastroduodenal junction WFH 14.14

  21. Small intestine • 3 parts • Duodenum- shortest, mostly secondarily retroperitoneal • Jejunum- mobile, about 2/5 of length of 6-7 meters • Ileum- about 3/5 of the 6-7 meters • Gradual transitions • Common features • Villi • Crypts of Lieberkühn • Segmental differences • Brunner’s glands in duodenum

  22. Small intestine M/D 2.38

  23. Duodenum with Brunner’s glands in submucosa and Peyer’s patch WFH 14.15a

  24. Schematic of ways that the surface area in the small intestine is increased: plicae circulares, villi, and microvilli WFH 14.16

  25. Villi and crypts of LieberkühnStem cells are in the crypts and migration is toward tip of villus.Muscularis mucosae extends into villi.WFH 14.18b

  26. Paneth cells secrete defensins. The lumen if the small intestine is virtually sterile.WFH 14.19a

  27. Transverse section of villus with lacteal in lamina propria WFH 14.20c

  28. Large intestine M/D 2.42

  29. Large Intestine • Cecum, appendix, colon, rectum, and anal canal • Haustrum (sacculation) haustra (plural) • Tenia coli is a band of longitudinal muscle • Cecum and colon only • 3 teniae (plural) • Mesocolic • Omental • free • Flexures of colon • Right colic, left colic, sigmoid

  30. Transverse section of colon at low magnification WFH 14.28

  31. Simple tubular glands of the colon secrete mucus. WFH 14.28b

  32. Ileocecal junction M/D 2.35c

  33. Transverse section of appendix showing extensive lymphoid tissueWFH 14.29a

  34. Lymphoid follicle in appendix WFH 14.29b

  35. Abrupt change in epithelium to stratified squamous at the recto-anal junction.Circumanal glands open into distal ends of columns of Morgagni WFH 14.30

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