Gastrointestinal System II

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Gastrointestinal System I | Main Anatomy Index | Liver, Gallbladder and Pancreas

Last updated 30 March 2006

This page was contributed by David Boshell.

Gastrointestinal System II

Structural organisation of the alimentary canal

  1. Mucosa
  2. Submucosa
  3. Muscularis externa
  4. Serosa or adventitia

Mucosa

  1. Protective - stratified squamous epithelium found in the oral cavity, pharynx, oesophagus and anal canal.
  2. Secretory - found in the stomach, where the mucosa consists of long, closely packed tubular glands which may be simple, or branching, depending on the region of the stomach.
  3. Absorptive - found in the small intestine, where the mucosa has finger like projections called villi, with intervening short glands called crypts (of Lieberkuhn).
  4. Absorptive/Protective - in large intestine, where the mucosa is arranged as closely packed, straight tubular glands with cells specialised for water absorption and mucous-secreting goblet cells for lubrication of the intestine.

Submucosa

Muscularis externa

Serosa and Adventitia

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The oesophagus

Gastro-oesophageal junction

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The stomach

  1. The cardia, near the oesophageal orifice, with cardiac glands
  2. The fundus (including the fundus and body as defined in gross anatomy), containing fundic glands
  3. The pylorus, proximal to the pyloric sphincter, with pyloric glands.

Fundic glands (Gastric glands)

  1. Mucous neck cells, localised to the neck region, with less prominent mucous cups, that secrete a more soluble mucous compared to that of the surface mucous cells.
  2. Chief cells, located deep within the glands, with round, basophilic, basal nuclei and apical zymogen granules containing their secretory product, pepsinogen.
  3. Large parietal (oxyntic) cells, mostly in the middle and upper portions of the gland, with round nuclei and an eosinophilic cytoplasm with an intracellular canalicular system, secreting HCl and Intrinsic Factor.
  4. Small enteroendocrine (APUD) cells, mostly at the base, with a clearer staining cytoplasm, that secrete the hormone gastrin into the lamina propria.
  5. Undifferentiated stem cells.

Cardiac glands

Pyloric glands

 

Gastro-duodenal junction

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The Small Intestine

  1. Tall columnar enterocytes, with basal nuclei and a striated border on the apical surface, reflecting their primary function of absorption.
  2. Mucous secreting goblet cells, most numerous in the terminal ileum, with basal nuclei and mucinogen granules in the apical cytoplasm.
  3. Paneth cells, found in the bases of the intestinal glands, characterised by strongly eosinophilic secretory granules containing the antibacterial enzyme lysozyme.
  4. Enteroendocrine cells, mainly in the lower parts of the crypts, with their main secretions being cholecystokinin (CCK), secretin and gastric inhibitory peptide (GIP), that increase pancreatic and gallbladder activity and decrease gastric secretion and motility.
  5. M (Microfold) cells, modified enterocytes covering the lymphatic nodules, characterised by microfolds instead of microvilli, that discharge their absorptions basolaterally, presenting their contents to intraepithelial lymphocytes to aid stimulation of GALT.
  6. Intermediate cells, the majority of cells in the lower half of the crypts, that are still undifferentiated, with characteristics of absorptive and goblet cells.

Gut Associated Lymphatic Tissue (GALT)

Ileo-caecal junction

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The large intestine

  1. Columnar absorptive cells, identical to the enterocytes of the small intestine, are the predominating cell type.
  2. Goblet cells, more numerous than in the small intestine, and are most prominent in the distal part of the large intestine, as they lubricate the increasingly solid faeces.

Caecum and Appendix

Recto-anal junction

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Michael Tam (c) 1998