STOMACH

• Stomach - an enlarged segment of the digestive tract that primarily functions as a storage and mixing chamber; lined with simple columnar epithelium
• Regions of the Stomach:

  • Esophagus
  • Lower Esophageal Sphincter (LES)
  • Fundus
  • Longitudinal muscle layer
  • Circular muscle layer
  • Oblique muscle layer
  • Body
  • Mucosa
  • Submucosa
  • Antrum
  • Pyloric Sphincter
  • Duodenum
• The stomach's epithelium forms numerous tubelike gastric pits, which are openings for the gastric glands
• 5 Types of Epithelial Cells of the Stomach:

  • Surface mucous cells - protects stomach wall from acid and digestive enzymes
  • Mucous neck cells - produce mucus
  • Parietal cells - produce HCl and intrinsic factor
  • Chief cells - produce pepsinogen
  • Endocrine cells - produce regulatory hormones
• Types of Endocrine Cells:

  • Enterochromaffin-like cells - produce histamine
  • Gastrin-containing cells - secrete gastrin
  • Somatostatin-containing cells - secrete somatostatin
• Chyme - food mixed with stomach secretions; primary function of the stomach is to mix and store this material
• Stomach secretions:

  • Mucus
  • Hydrochloric acid
  • Gastrin
  • Histamine
  • Intrinsic factor
  • Pepsinogen
• Intrinsic factor - a glycoprotein that binds with vitamin B12, an important vitamin for DNA synthesis and RBC production, making the vitamin more readily absorbed in the ileum
• Pernicious anemia - a type of anemia resulting from a lack of vitamin B12 absorption
• Hydrochloric acid - has a pH between 1 and 3; provides the proper pH for the activation of pepsin; stops carbohydrate digestion by inactivating salivary amylase
• Pepsinogen - packed in zymogen granules which are released by exocytosis when secretion is stimulated; the inactive form of the protein-digesting enzyme pepsin
• Approximately 2-3 L of gastric secretions are produced each day, with up to 700 mL being secreted as a result of a typical meal.
• Chemical messengers/hormones that regulate stomach secretions:

  • Gastrin - increase gastric secretion
  • Secretin - decreases gastric secretion
  • Cholecystokinin - slightly decreases gastrin secretion
• 3 Phases of Regulation of Stomach Secretion:

  • Cephalic - "get started"
  • Gastric - "go for it"
  • Intestinal - "slow down"
• Peptic ulcer - caused when gastric juices digest the mucosal lining of the digestive tract; due to infection by Helicobacter pylori
• Gastroesophageal reflux - reflux of acidic chyme from the stomach into the esophagus; chronic reflux occurring more than twice a week is called gastroesophageal reflux disease (GERD)