Overview of GIT Flashcards
describe anatomy of stomach?
pylorus - sphincter that prevents food leaving stomach
parietal cells - for acid secretion
chief cell - release inactive pepsinogen which is converted to pepsin (active form) in acidic environment - proteolytic
how can filling the stomach lead to acid secretion?
filling the stomach bag leads to distension of the stomach walls which can activate G cells to release gastrin - GASTRIC PHASE of acid secretion
what is the difference b/w a resting and activated parietal cell?
resting parietal cells - tubulovesicles are purple, isolated, contain lots of mitochondria and a nucleus
activated cell - tubulovesicles form intracellular canaliculi - H+/K+ ATPase pump gets localised on the luminal surface of the cell
what hormones regulate parietal cell acid secretion
Acetylcholine, gastrin, histamine
what are the neurocrine, endocrine and paracrine mechanisms?
acetylcholine is released onto basolateral surface by postganglionic neurones - neurocrine
gastrin released by antral G cells into bloodstream, which then binds to parietal cells - endocrine
histamine released by mast cells in lamina propria of parietal cells - paracrine
describe the gastric phase of acid secretion
distension of stomach or digestion of proteins causes G cells to release gastrin - which released into bloodstream
gastrin will bind to ecl cell receptors which stimulate mast cells to release histamine - histamine stimulates H+/k+ ATPase pump and acid secretion occurs - protons released into lumen of stomach
H+ will bind to D cells which secrete somatostatin and this acts on G cells to inhibit further gastrin release - NEG FEEDBACK MECHANISM
components of pancreatic juice?
bicarbonate to neutralise duodenum contents
proteases - trypsinogen
amylase
lipases
how is bile secretion regulated?
bile salts produced by liver
when chyme from stomach enters small intestine - 2 hormones are released:
- cholecystokinin (CCK)
- secretin
CCK contracts gall bladder
secretin increases bile flow rich in HCO3-
