Editing Stomach (section)

=== Gastric acid secretion ===

** Secreted by parietal cells      via the hydrogen-potassium-ATPase pump
** Three regulators stimulate      release:
*** Acetylcholine - from vagal       nerve
*** Gastrin - hormonal
*** Histamine - paracrine       effects
** Inhibition by somatostatin
** There is always a basal      level of secretion, approximately 10% of total output, which is reduced      by vagotomy and anti-histamine drugs
** Normal total 24 hour output      of gastric fluid is ~1.5L
**

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* Three phases of gastric acid     secretion
** Cephalic
*** Sight, smell, thought or       taste of food
*** Probably mediated by vagal       nerve
** Gastric
*** Begins when food enters the       gastric lumen
*** Mediated via protein       interactions with antral G cells, and mechanical distension of the       stomach
*** Accounts for most (70%) of       acid secretion
** Intestinal
*** Initiated by entry of chyme       into the duodenum, which stimulates gastric release and suppresses       gastric motility
*** Lasts as long as chyme       remains in the proximal small bowel
* Pharmacological regulation of     acid secretion
** See 'GORD' under medical      management