GI 2 - acid Flashcards
how much gastric juice does a human secrete per day
2.5 litres
what do peptic/ chief cells release
pro enzymes like prorennin and pepsinogen
what do parietal cells secrete
HCl
what are 3 reasons that gastric secretions are so acidic?
to promote proteolysis (convert pepsinogen to pepsin)
kill pathogens
aids in iron absorption
which form of iron is better to be absorbed, which is favoured in acidic?
Fe2+ is better absorbed than Fe3+
Fe2+ is made in acidic environment
what is the main protective mechanism of the stomach wall from acid
mucosal cells that secrete prostaglandins
what are the 2 main prostaglandins that mucosal cells secrete
PGE2 and PGI2
what do mucosal cells secrete
PGE2 and PGI2 (prostaglandins), also mucus and bicarbonate
what are the targets for PGE2 and PGI2
EP1, EP2, EP3, EP4
where do prostaglandins act to stimulate mucous secretion
EP4 receptors on mucosal cells
where do prostaglandins act to stimulate bicarbonate ion secretion
EP1/2 receptors on mucosal cells
what happens when EP4 receptors on mucosal cells are activated
release mucus
what happens when EP1/2 receptors on mucosal cells are activated
stimulate bicarbonate ion secretion
what is the pH of the stomach lumen
1-2
how is the stomach wall physically protected from mucous? What is the ph of this?
mucosal surface forms gel-like protective surface, pH 6-7
what kind of prostaglandins receptors are on enterochromaffin like cells
EP2/3
what happens when EP2/3 on enterochromaffin like cells are activated
inhibits release of histamine
what does histamine do and how
stimulates acid production via H2 receptors
what kind of prostaglandins receptors are on vascular cells
EP2/4
what happens when prostaglandins act on vascular EP2/4 receptors
vasodilation, improve blood flow to mucosal layer
what are the 3 cell targets of prostaglandins
mucosal cells, enterochromaffin like cells (ECL), vascular cells
what is the concentration of HCL secretion by parietal cells
150mM
how is Cl- secreted by parietal cells
actively (alongside K+) (on lumen side)
how is K+ secreted by parietal cells
actively (alongside Cl-) (on lumen side)
what kind of transporter is the Cl- K+ mechanism in parietal cells
it is co transport, 2ary active (on lumen side)
what provides the energy for the Cl- K+ co transport
K+ being exchanged in a H+/K+ ATPase (H+ into lumen, K+ back inside)
what is the pH inside the parietal cell
7.2
what is the pH inside the stomach lumen
1-2
what kind of gradient is the ATPase pumping against in the parietal cell
HUGE gradient, 10^5 fold gradient
what is the source of H+ in parietal cells
carbonic anhydrase generating H+ and HCO3- from H2O and CO2
what is the source of Cl- in parietal cells
HCO3- exchanges for Cl- (on blood side)
what is the pH of the HCl secreted by parietal cells
less than 1!
where is histamine released (and where in the cell specifically)
basally released from ECL cells
which cell releases histamine
ECL cells
where does histamine from ECL cells act
on parietal cell H2 receptors
what happens once histamine acts on parietal H2 receptors
activates Gs, cAMP –> proton pump
which cells release gastrin
G cells
what causes the release of gastrin by G cells
nerve stimulation and stomach contents
what are 2 example of stomch contents that stimulate HCl release
amino acids, Ca++
what does gastrin do? where does it act?
it acts on CCK2 receptors on ECL cells, elevates [Ca++]i to stimulate release of histamine
what do G cells release
gastrin
what do ECL cells release
histamine
where is ACh released
postganglionic cholinergic neurons
where does ACh act (2)
on parietal M3 receptors AND D cells
what happens when ACh acts on M3 receptors (where are they)
parietal cell, stimulates proton pump via elevation of [Ca++]i
what does ACh do to D cells
inhibits somatostatin release
what does ACh do to somatostatin release and how
inhibits its release from D cells
what do prostaglandins do in the HCl pathway (3)
inhibit histamine production, increase HCO3- and mucous secretion, vasodilation
where is somatostatin released (and what cell types)
from D cell in stomach
where does somatostatin act
SST2 receptors on G cells, ECL cells, parietal cells
what does somatostatin do to G cells
acts on SST2 receptors on G cells to inhibit gastrin release
what does somatostatin do to ECL cells
inhibit histamine release
what does somatostatin do to parietal cells cells
inhibit acid secretion
what are stomach ulcers and how can they be serious?
bleeding, perforation leading to stomach contents entering body cavity and causing peritonitis
what is GERD and how can it be serious?
damage to esophageal epithelium can lead to barretts esophagus (damaged, precancerous)
what are 3 examples of these GI diseases
ulcer, GERD, hiatal hernia
what is the problem with Hiatal hernia
similar with GERD and esophageal acid reflux, similar treatment
(dw too much bout this one)