Inflammatory reaction in the stomach. Typically involves the mucosa; seldom the full thickness of the stomach wall:

• Patchy erythema of gastric mucosa: A common endoscopic finding; usually insignificant
• Erosive gastritis: A reaction to mucosal injury by a noxious chemical agent (e.g., drugs [especially NSAIDs] or alcohol)
• Reflux gastritis:
  • A reaction to protracted reflux exposure to bile and pancreatic juice, usually associated with a defective pylorus
  • Typically limited to the prepyloric antrum
• Hemorrhagic gastritis (stress ulceration):
  • A reaction to hemodynamic disorder (e.g., hypovolemia or hypoxia [as in shock])
  • Also common in ICUs
• Infectious gastritis:
  • Commonly associated with Helicobacter pylori (possibly causative, maybe opportunistic)
  • Viral infection, usually as a component of systemic infection, is common.
  • Significant infection by other specific microbes is rare.
• Gastric mucosal atrophy, sometimes called atrophic gastritis:
  • Frequent, in varying degrees, in the elderly
  • Invariable in primary (pernicious) anemia
• Synonym(s): Erosive gastritis; Reflux gastritis; Hemorrhagic gastritis; Acute gastritis
• Neutrophil cellular infiltration in acute gastritis
• Patches of lymphoid follicles noted in chronic gastritis, along with plasma cells and macrophages
• More than 50% of humans are colonized with H. pylori

• Persons >60 often harbor H. pylori infection

• Gastritis rarely occurs in infants or children.