12 Esophagus & Stomach

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  1. What are some ways in which the alimentary canal protects the body from pathogens?
    • 1. Specialized epithelial cells (M-cells) for antigen sampling
    • 2. Large aggregations of diffuse and nodular lymphoid tissues (Peyer's patches in ileum)
    • 3. Mucus coating traps potential pathogens (eg. bacteria)
  2. GI Tract Organization
    • 1. Lumen →
    • 2. Mucosa (epithelium, lamina propria, muscularis mucosa)
    • 3. Submucosa (may have glands, nerves)
    • 4. Muscularis Externa
    • 5. will either have an Adventitia or Serosa, depending on where in GI tract you are
  3. Mucosa
    • lined by epithelium
    • covered by the Lamina Propria: loose CT
    • then covered by the Muscularis Mucosa: smooth muscle layer
    • all together = MUCOSA (epithelium, loose CT, SM muscle)
  4. Mucosa
    • another muscular layer comprised of three components
    • 1. muscularis mucosa: thin layer of smooth muscle that can assist in emptying glands
    • 2. lamina propria: loose CT that contains immune cells
    • 3. luminal epithelium: epithelial layer covering entire luminal surface of GI tract
    • contains many of the structural and functional specializations of the different regions of the GI tract
    • (eg. intestinal villi, crypts, gastric pits or glands)
  5. Submucosa
    • a connective tissue layer that lies between the muscularis externa and the muscularis mucosa
    • contains blood vessels, nerves, parasympathetic ganglia, & lymphatics
  6. Muscularis Externa
    • muscular layer deep to the serosa that consists of two layers of smooth muscle – an outer one that is longitudinal and inner one that is circular
    • wave-like contractions of these opposed muscle layers (peristalsis) results in the efficient propulsion of food
    • contractions are regulated by parasympathetic nerves & ganglia (myenteric plexus) that lie between the muscle layers
  7. Serosa
    • outermost layer along most of the GI tract
    • consists of two components: 1) simple squamous epithelium (mesothelium) that forms a slippery surface allowing intestines to slide over one another & 2) adventitia made of loose CT
    • the serosa contains blood vessel, nerves & lymphatics
  8. What is the sole conduit for blood vessels/nerves to enter AND exit the intestines, and for lymphatics to exit?
    the mesentery
  9. Adventitia
    • the outermost layer connecting the GI tract to the body wall in regions where there is NO serosa, due to the absence of an epithelium
    • most of the esophagus & part of the gall bladder
  10. Luminal Epithelium
    • In the esophagus it is a stratified squamous epithelium
    • throughout the remainder of the tract it is a simple columnar epithelium (gastric epithelium)
    • this epithelium is also continuous with the epithelial lining of the ducts and glands of the accessory digestive organs (the pancreas, liver & gall bladder)
  11. Where is the Serosa layer located in the esophagus?
    • the outer esophagus lining = Adventitia until it crosses the diaphragm
    • in the Thorax the outer layer = Adventitia
    • within the abdominal cavity it's outermost region consists of a Serosa
  12. Where might skeletal muscle be found in the esophagus?
    in the upper 1/3
  13. Where might both skeletal & smooth muscle be found in the esophagus?
    in the middle 1/3
  14. Where is only smooth muscle found in the esophagus?
    lower 1/3
  15. How does the muscularis mucosa run in the esophagus?
  16. Myenteric/Auerbach's
    located in between muscle layers of the gut & esophageal wall of the Muscularis Externa
  17. Meissner's Plexus
    • nerve plexus in the submucosa that innervates the muscularis mucosa to control it’s contraction
    • further down in the GI system it controls the emptying of glands
  18. Where are regions of the GI tract where the submucosa contains glands?
    1. esophagus: producing a lubricating/protective mucous

    visually the only place there's a submucosal gland deep to a SSNKE = esophagus

    2. duodenum (small intestine): neutralizes partially digested acidic chyme (food from the stomach)
  19. What happens to the luminal epithelium at the esophageal-stomach junction (squamo-columnar)?
    • it undergoes an abrupt change from the stratified squamous epithelium (of the esophagus) to the simple columnar epithelium (the gastric epithelium) of the stomach (and subsequently the intestines)
  20. Barrett’s Esophagus
    • when acidic contents of the stomach chronically bypass the lower esophageal sphincter (one-way valve), the esophageal SSNKE epithelial cells can undergo a transition to simple columnar epithelium
    • associated with the subsequent development of esophageal adenocarcinoma (lethal)
  21. Regions of the Stomach
    • Cardiac region: short pits & glands; mucous & enteroendocrine cells
    • Fundus/Body region: short pits, long glands; thick surface mucous, mucous neck (clear), parietal, chief, & enteroendocrine cells
    • fundus also has SM muscle cells running through mucosa to contract it, forcing gland contents into lumen 
    • Pyloric region: long pits, short glands; mucous & enteroendocrine cell
  22. Where is intrinsic factor synthesized?
    • in the stomach by parietal (fried egg) cells
    • made in the stomach but used in the gut for the absorption of vitamin B12
    • issues with stomach lining or parietal cells can cause Vitamin B12 deficiency & eventually pernicious anemia
  23. Where is there a third, oblique muscle layer present in the Muscularis Externa of the GI tract?
    • in the stomach where food is also subjected to a grinding action
    • outer (longitudinal), middle (circular) & inner (oblique)
  24. What are the 5 types of cells in the glands of the stomach (including the pits)?
    1. surface mucous: simple columnar; protective against acid made in stomach

    2. mucous neck

    3. enteroendocrine

    4. parietal: make HCl & intrinsic factor

    5. gastric chief: make pepsinogen --> pepsin in acid

    the cardiac & pyloric glands contain ONLY the first 3 cell types

    the fundic/gastric glands contain all five
  25. What are the general turnover rates for gastric cells as a result of stem cell proliferation (derived from base of gastric glands)?
    • mucous: 3-5 days
    • endocrine: weeks
    • chief & parietal: 90-200 days (months)
    • PAS stained surface mucus & mucous neck cells
    • mucus cells making thick bicarbonate mucus that serves to protect the stomach lining
    • Parietal cells
    • make HCl & Intrinsic Factor
    • look like red (eosinophilic) fried eggs
    • packed with mitochondria (red dots)
    • clear areas in cell represent Intracellular Canaliculus - implies cells were active (secreting HCl)
    • purple cells = chief cells
    • basophilic because of abundant RER making pepsinogen
    • typical protein secreting cells
    • have a ton of zymogen granules that contain inactive enzymes: pepsinogen, lipase, chymosin
  26. Pepsinogen
    • when released into acid environment of gut from chief cells, the low pH (<5) causes autocatalytic activity, turning pepsinogen into pepsin
    • when pepsin gets to neutral pH of duodenum, it's inactivated
  27. Atrophic Gastritis
    • chronic inflammation of the stomach mucosa leading to loss of gastric glandular cells & their eventual replacement by intestinal & connective tissue
    • ability for stomach to secrete substances is impaired (deficiency in intrinsic factor leads to vitamin B12 deficiency, pernicious anemia)
    • can be caused by autoimmunity or by Helicobacter pylori infection
    • will see lymphocyte infiltration
  28. H. Pylori Infection
    • bacteria convert urea to ammonia via urease
    • this neutralizes acid of the stomach, & allows bacteria to penetrate into mucosal lining
    • bacteria have proteins that look similar to stomach lining itself, so when the stomach makes antibodies against the bacteria, it damages self (autoimmune attack to the stomach lining)
    • if chronic this can lead to Gastritis
  29. Enteroendocrine Cells
    • an cell abundant in the GI tract that requires special staining
    • make numerous products including Gastrin, Somatostatin, Ghrelin, Enterochromaffin
    • here they're visualized in the pyloric region (end) of the stomach (can see long pits, short glands)
  30. Gastrin
    a peptide hormone secreted by Eneteroendocrine (G) cells that stimulates secretion of HCl by parietal cells
  31. Somatostatin
    • inhibits Gastrin release
    • also inhibits release of CCK & Secretin, inhibiting pancreatic & gall
    • bladder secretions
  32. Pyloric Sphincter
    • the last part of the stomach overlies the pyloric sphincter, a thickened part of the Muscularis Externa that closes the stomach & only opens when digestion within the stomach is sufficient (material is liquid)
    • as the sphincter opens it squirts that fluid into the duodenum (1st part of the SI)

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12 Esophagus & Stomach
2016-10-17 15:22:55
MedFoundationsI Histology Exam3
Histology Exam 3
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