Gastric Secretion Flashcards
role of chief cell
secrete pepsinogens
what is a zymogen
an inactive precursor to an active enzyme or substance e.g. pepsinogen –> pepsin
cells that secret HCl
parietal cells
secretions of parietal cells
HCl and intrinsic factor
what is intrinsic factor important for
transport of vit B12
mucus is secreted by what cells type in the gastric gland
surface and neck mucous cells
production of stomach acid requires entry of what two substances into the cell
Cl and CO2
in stomach acid production what is released back into the blood
bicarbonate (HCO3)
pH of stomach acid
<2
what moves across the leaky tight junctions of stomach epithelium as stomach acid is made
water
3 substances that stimulate gastric acid secretion
gastrin, histamine and acetylcholine
where does gastric acid production occur
in parietal cells
how do gastrin, histamine and ACh stimulate gastric acid production
by stimulating the K/H primary active pump
mechanism of histamine on acid secretion
- unique receptor when in gut stimulates a G protein coupled to AC
- AC makes ATP to cyclic AMP
- cAMP acts on proteins kinases to stimulate K/H pump
how do prostaglandins inhibit secretion
turns off AC thus stopping cAMP being made
neurocrine control gastric secretion
ACh
endocrine control of gastric secretion
gastrin
paracrine control of gastric secretion
histamine
what cells secrete histamine
ECL cells
what substances stimulate ECL cells to release histamine
gastrin and ACh
what stimulates G cells to release gastrin
- peptides in stomach lumen
2. vagus nerve
what initial input triggers the vagal and enteric reflexes for gastric secretion
food in stomach causing distension
presence of acid and fat has what effect on gastrin and HCl secretion
inhibition
reflex that communicates acid in duodenum to stop gastrin and hence gastric secretion
enterogastric (splanchnic reflex)
what is an enterogastrone
a hormone released from gland cells in the duodenum
what are the 3 main enterogastrones
secretin, cholecystokinin (CCK) and GIP
enterogastrones are released in response to
acid, fatty acids, monoglyceridres and hypertonic solutions
enterogastrones effect on acid secretion and gastric emptying
inhibit acid secretion
reduce gastric emptying
inactive precursor of pepsin
pepsinogen
what pH changes pepsinogen to pepsin
pH <3
what pH inactivates pepsins
neutral (i.e. pH 7)
how does mucus protect against damage by acid and pepsin
pepsin will be inactivated by neutral pH (high bicarbonate)
physical barrier to acid
which cells produce intrinsic factor
parietal cells
lack of intrinsic factor and hence B12 absorption cause what condition
pernicious anaemia
