Digestive Infections


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•  Helicobacter pylori infection as a cause of stomach ulcers

Stomach ulcers are inflammed and damaged areas in the stomach wall, typically caused by exposure to gastric acids

  • There is a strong positive correlation between Helicobacter pylori infection and the development of stomach ulcers

Helicobacter pylori is a bacterium that can survive the acid conditions of the stomach by penetrating the mucus lining

  • H. pylori anchors to the epithelial lining of the stomach, underneath the mucus lining
  • An inflammatory immune response damages the epithelial cells of the stomach – including the mucus-secreting goblet cells
  • This results in the degradation of the protective mucus lining, exposing the stomach wall to gastric acids and causing ulcers
  • The prolonged presence of stomach ulcers may lead to the development of stomach cancer over many years (20 – 30 years)
  •  H. pylori infections can be treated by antibiotics (previously, stomach ulcers were considered stress related and not treatable)

Stomach Ulcer Formation

stomach ulcers

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•  Dehydration due to cholera toxin

Vibrio cholerae is a bacterial pathogen that infects the intestines and causes acute diarrhoea and dehydration

  • The associated disease – cholera – can kill within hours unless treated with oral rehydration therapies

V. cholerae releases a toxin that binds to ganglioside receptors on the surface of intestinal epithelium cells

  • This toxin is internalised by endocytosis and triggers the production of cyclic AMP (a second messenger) within the cell
  • Cyclic AMP (cAMP) activates specific ion channels within the cell membrane, causing an efflux of ions from the cell
  • The build up of ions in the intestinal lumen draws water from cells and tissues via osmosis – causing acute diarrhoea
  • As water is being removed from body tissues, dehydration will result if left untreated

Mechanism of Action of Cholera Toxin