Editing Helicobacter pylori (section)

== '''Pathophysiology''' ==

* Spiral-shaped, flagellate,     gram-negative bacteria
* Resides in gastric-type     epithelium within or beneath the mucus layer
** Heterotopic gastric mucosa      in proximal oesophagus
** Barrett oesophagus
** Gastric metaplasia in the      duodenum
** Within a Meckel diverticulum
** Heterotopic gastric mucosa      in the rectum
* Adaptations:
** Mucolytic enzymes including      protease - protect from mucus
** Urease - creates an alkaline      microenvironment
** Propulsion by flagella
** Attachment to epithelium -      receptor-mediated adhesion
** Catalase - allows the      organism to survive host defence inflammation
* Proposed mechanisms of     injury:
** Production of toxic products      that cause local tissue injury
*** Not present in all strains,       but when they are present, more likely to cause injury:
**** CagA -        cytotoxin-associated gene A - necessary for VacA expression - disrupts        cell integrity
**** VacA - vacuolating        cytotoxin - stimulates apoptosis of cells
*** Several others
** Induction of a local mucosal      immune response - which is the mechanism by which most damage is caused
*** Produces antigenic       substances such as lipopolysaccharides
*** Lead to increased local       IL-1, IL-6 and TNF-alpha
** Alterations to gastrin      levels and changes in acid secretion
*** See below
*** Acid can be increased or       decreased during the acute phase (depending on whether there is       antral-predominant disease or pan-gastritis respectively) and decreased       during the chronic phase
** Gastric metaplasia in the      duodenum
*** Likely occurs as a       protective response to decreased duodenal pH
*** Allows H. pylori to       colonise the duodenum
* Pattern of injury
** Almost all infected patients      have antral gastritis, as opposed to NSAID ulcers, of which only 25% have      antral gastritis
** Infection tends to be      confined initially to the antrum
** Ulcers frequently found in      the duodenum/antrum
** >90% of duodenal ulcers      are associated with H pylori; 60% of gastric ulcers