stomach physiology Flashcards
what are the 5 parts of the stomach?
cardia, fundus, body, antrum & pylorus
what are the functions of the stomach?
- store & mix food
- regulate emptying of chyme into the duodenum
- kill microbes
- secrete proteases
- secrete intrinsic factor
- activate proteases
- lubrication
- mucosal protection
- dissolve and continue digestion
what are the 4 cells in the stomach? & what do they secrete?
mucous cells - secrete mucous
parietal cells - secrete gastirc acid and intrinsic factor
cheif cells - secrete pepsinogen
enteroendocrine cells - secrete serotonin, gastrin, somatostatin and histamine
What cells are present in the gastric pit and what order are they in?
superficially to deep
- mucous secreting neck cells
- parietal cells
- cheif cells
what are the phases of gastric acid secretion regulation?
activation = cephalic and gastric inhibition = gastric and intestinal
What happens in the cephalic phase of gastric acid regulation?
- Parasympathetic nervous system is activated
- activated by the sight/smell/taste/chewing of food
- releases Ach which acts directly stimulating parietal cells
- Ach also stimulates the release of gastrin & histamine
what happens in the gastric activation phase of gastric acid regulation?
- gastric distension, presence of peptides and amino acids causes gastrin to be released by G cells
- gastrin acts directly on parietal cells increasing the number of proton pumps on it’s luminal membrane
- also triggers the release of histamine
- histamine acts directly on parietal cells and causes more HCl to be secreted
what happens in gastric inhibition phase of gastric acid regulation?
- Low pH in the stomach lumen inhibits gastrin sceretion
- indirectly inhibiting histamine production
- Low pH also stimulates delta cells to secrete somatostatin which inhibits parietal cell activity
What happens in the intestinal phase of gastric acid regulation?
In the duodenum:
- distension
- Low pH
- hypertonic contents
- presence of amino acids & fatty acids
all trigger the release of - secretin & CCK
Secretin - inhibits gastrin production & stimulates somatostatin production
CCK - inhibits gastric emptying, inhibits parietal cells & stimulates pancreatic enzyme production from the pancreas and gall bladder contraction.
How is gastric acid secreted?
- H2O is split into H+ & OH-
- H+ is pumped in to the lumen of the stomach through ATPase K+/H+ pump (energy dependent)
- Cl- follows through a Cl- channel
- carbonic anhydrase converts CO2 & H2O into bicarb which then dissociates to give a H+ to replace the one lost from H2O previously
- HCO3- is then pumped out of the cell into a capillary whilst a Cl- is pumped in via an antiporter
what activates pepsinogen?
- low pH cleaves pepsinogen to pepsin
- Pepsin then cleaves pepsinogen as well in a +ve feedback loop
what protects gastric mucosa from the gastric acid?
mucous produced by neck cells in the gastric pits and goblet cells in mucosa which is alkaline & contains bicard
- tight junctions between epithelia cells
- replacement of damage cells
what is the rate of peristaltic waves in the stomach?
3 per minute
what increases the strength of peristaltic waves?
- gastrin
- gastric distension mediated by mechanoreceptors
what are the pacemaker cells called in the stomach?
interstitial cells of cajal
