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Flashcards in Histology - GI Tract Deck (20):

GI Tract Structure

Mucosa (mucus membrane)
 All luminal regions lined by epithelium
 Lamina propria – connective tissue
 Muscularis mucosa
Submucosa – connective tissue
Meissner’s (Submucosal) Plexus
Muscularis Externa – responsible for peristalsis
 Inner circular layer
• Auerbach’s (Myenteric) plexus
 Outer longitudinal layer
Adventitia or Serosa
 Adventitia – connective tissue that is continuous with surrounding organ
 Serosa – this slippery membrane


Function of Lumenal Epithelium lining

esophagus - protective
stomach - secretory
small intestine - absorptive


Generaly 2 Types of Glands

 Found in lamina propria or submucosa
 Found outside of GI tract but send ducts through walls of GI tract and into the lumen
• Bile duct & pancreatic duct


Esophagus Structure

-mucosa - Non-keratinized stratified squamous epithelium – cells are living (protection)


Esophagus Glands

 Submucosal glands – found in submucosa throughout esophagus
• Secrete mucin that lubricates the esophagus
 Cardiac glands – secrete mucin; found in lamina propria of mucosa lining at 2 sites
• Junction of esophagus and stomach
• Between cricoid cartilage and 5th tracheal ring


Stomach Structure

4 regions (cardiac, fundus, body, pyloric)
o Rugae - very large folds along surface that run in longitudinal direction that involve the mucosa lining and submucosa
o Simple columnar epithelium
o Gastric Pits – where digestive juices (HCl, pepsinogen) are dumped into lumen
 Each pit is continuous with glands that lie deep in lamina propria (NOT submucosa)


Stomach Regions and Glands

vary by region of stomach
 Cardiac region – cardiac glands
 Fundus & body regions – gastric glands
 Pyloric region – pyloric glands


Gastric Gland cells

Chief cells (major type)
parietal cells
mucus neck cells
surface mucous cells
enteroendocrine cells


Chief Cells

-pepsinogen and Gastric Lipase
• Pyramid shaped found mainly in base of gland
• Filled with RER and golgi


Parietal Cells

– HCl and Intrinsic Factor
• Round and filled with mitochondria and tubular vesicular elements
• Contains deep invaginations called canaliculi which are lined with microvilli


Mucus Neck Cells

• Confined to neck region of gastric gland and squeezed between parietal cells
• Secretes acetic mucin (compared to neutral mucin of other cells)


Surface Mucus cells

– secretes neutral mucin


Enteroendocrine Cells

a.k.a. (argentaffin) Cells because of affinity for silver salts
• Various endocrine products secreted into blood vessels of lamina propria
• Found throughout small intestine also


Cardiac and Pyloric Glands

 Lined mostly by mucus neck cell; some enteroendocrine cells
 Rarely find parietal or chief cells
 Cardiac glands – gastric pits are shallow and glands are relatively straight
 Pyloric glands – very deep gastric pits and glands themselves are very coiled


Small Intestine General Structure

o Duodenum (first 10 inches), jejunum (next 2/5ths), ileum (last 3/5ths)
o Plicae circularis – large folds that increase surface area; Begin towards end of duodenum and disappear half way through ileum
o Intestinal villi – line the mucosa on top of plicae; move up and down (NOT stationary)
 Central lacteal – lymphatic vessel runs through center of each villi
o Intestinal glands (Crypts of Lieberkuhn) appear as invaginations into lamina propria; high turnover rate 2-3 days


Intestinal Gland Contents

aka Crypts of Lieberkuhn
 Goblet cells– filled with mucin granules and secretes mucous; appear white/milky
 Intestinal absorptive cells – tall and columnar dense microvilli along lumen side; pentagonal/hexagonal shaped; brush border containing glycocalyx (sugar rich coat)
 Enteroendocrine cells – line the lateral borders
 Zymogenic (Paneth) cells – bottom of gland; contains granules with zinc and lyxozyme


Distinguishing Characteristics in Small Intestine

 Intestinal villi get less prominent and fewer throughout the small intestine
 Increase in relative number of goblet cells to intestinal absorptive cells throughout length
 Duodenum – numerous branched mucus glands (Brunner’s glands) in submucosa; secrete alkali mucin that neutralizes acidic chyme; villi in duodenum are V shaped and tightly packed together
 Ileum – numerous lymphatic nodules (Peyer’s Patches); villi are less numerous and slim


Large Intestine Structure (Differences from Small Intestine)

 NO villi
 Crypts of Lieberkuhn are DEEPER (0.5-0.75mm vs. 0.3-0.5)
 Increase in number of goblet cells relative to number of intestinal absorptive cells
 Few if any Paneth or enteroendocrine cells
 Modified Muscularis externa (EXCEPT IN APPENDIX) – 3 discrete bands (teniae coli)
Appendix typically full of debris and possesses large amount of lymphatic tissue


Anus/Rectum Structure

• Anal/rectal columns – longitudinal folds in upper portion of anal canal
o Lower portion of anal canal is lined by non-kertinized stratified squamous epithelium that is continuous with keratinized squamous epithelium of skin


Folds in various areas of GI tracts

stomach - rugae
small intestine - plicae circularis
anal canal - rectal columns