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GI Histology (Esophagus (Muscularis Externa (Proximal 1/3 skeletal muscle,…

- - - - Stem Cells - undifferentiated cells that give rise to other cell types in the glands and gastric pits
      - Mucous Cells - line lumen of gastric pits, secrete protective mucous layer rich in bicarbonate ions
      - Parietal Cells - predominate in the upper segment of the gastric gland, produce HCl and intrinsic factor (vitamin B12 absorption), important for conversion of pepsinogen to pepsin (proteolytic enzyme that digests most proteins)
      - Chief Cells - secrete inactive proenzyme pepsinogen into the lumen of the gland
      - Enteroendocrine Cells - secrete hormones that have effects on gut motility (serotonin) and HCl secretion (gastrin)
- - - - Enterocytes (absorptive cells) - covered in microvilli to increase surface area, absorb carbohydrates, proteins, lipids, vitamins, Ca and Fe and transport to blood or lymph
      - Goblet Cells (mucus-secreting) - interspersed among enterocytes covering the villi, provide lubrication throughout (greater numbers further down), stain clear
      - Paneth Cells (lysozyme-secreting) - at the base of the crypt, stain orange-red from cytoplasmic granules filled with lysosome (antibacterial), TNF-alpha (pro inflammatory factor), defenses (antibacterial, anti-parasitic), synthesize and secrete antimicrobials and factors to sustain/modulate stem and progenitor cells to rejuvenate epithelium
      - Enteroendocrine Cells (hormone-secreting) - release factors in response to lumenal contents, such as cholecystokinin (small peptides, amino acids, fatty acids), secretin (H+, fatty acids), gastric inhibitory peptide (glucose, amino acids, fatty acids), glucagon like peptide (glucose, amino acids, fatty acids)
      - Stem Cells (replace enterocytes and goblet cells)