Gastric Secretion Prunuske Flashcards
How long does food usually hang out in stomach?
~4 hours
Main enzyme in stomach?
Pepsin
What part of the stomach is important as a secretion reservoir and is important for acid secretion?
Fundus and body
What happens in the antrum?
Mixing and grinding
*Technical word is…Truition
Where are the oxyntic/parietal glandular mucosa?
Body
What cells secrete pepsinogen?
Chief cells
What do parietal (oxyntic) cells secrete?
HCl
Intrinsic factor
Gastroferrin
Do parietal cells and chief cells get turned over regularly?
Nope, they are pretty stable!
What cells secrete gastrin?
Where are they?
G cells in the Antrum
What does gastrin do?
Activates parietal cells in the fundus/body to secrete acid!
What are the 2 triggers for gastrin release from G cells?
- Seeing food or stomach distension causes vagal stimulation causing release of Gastrin-releasing peptide (GRP)
- Aromatic amino acids in the lumen
What 3 things come in to bind to parietal cells to activate acid secretion?
Gastrin
Histamine
Ach
What does Atropine do to gastric acid secretion?
Inhibit!
*Its a muscarinic antagonist
Where does Histamine get released?
ECL cells
*Another target of gastrin…it binds to them and triggers histamine release!
Where are H+/K+ ATPases found in pareital cells?
Tubulo-vesicles
What happens to tubulovesicular cells when the parietal cells are stimulated?
They fuse with the canalicular membranes to increase their density at the apical membrane!
What is the consequence of your Na+/K+ ATPase being active on basolateral membrane?
Alters electrical membrane potential b/c pumping out 3 Na for every 2 K coming in…going to have low sodium inside these cells.
There are potassium channels on the apical surface
What special enzyme is active in parietal cells to generate H+ and Bicarbonate?
Carbonic anhydrase!
“Alkaline tide”
Blood in that immediate region is at a higher pH because bicarbonate is being excreted by parietal cells into the bloodstream
What organelle is abundant in parietal cells?
Mitochondria!
*Lots of ATP generation needed
What do proton pump inhibitors bind?
H+ K+ ATPase
So they directly interfere with H+ ions being pumped into lumen!
Where are D cells?
Adjacent to our G cells in the antrum
What do D cells release to inhibit G cells?
When are they going to release it?
Somatostatin!
If pH is really low and you don’t need active parietal cells! pH
Is there more or less somatostatin released when you eat food?
Less!
Because as food enters the stomach, the pH rises…therefore more gastrin is needed so less somatostatin is released!
What do prostaglandins do in parietal cells?
Inhibit cAMP formation
**Fill in why this is important
Which hormone is secreted due to increase in H+ in duodenum?
What does this block the secretion of?
Secretin
Histamine by ECL cells
What is required for B12 absorption?
Intrinsic factor
In what form is pepsinogen secreted?
As a proenzyme
*Doesn’t become active until it gets to gastric lumen
What cells start the process of enzymatic digestion of protein and fat?
Chief cells
What two things are positive regulators of chief cell secretion?
ACh
Gastrin
What inhibits chief cell secretion?
Secretin
What is Zollinger-Ellison Syndrome?
Gastrinoma!
GASTRIN-secreting tumor in PANCREAS or SMALL INTESTINE
Excess H+ secretion and hyperplasia/hypertrophy of parietal cells
*Most patients develop gastric ulcers
What is peptic ulcer disease?
Hyperacidity…Deterioration of gastro-mucosal barrier
Infection from what organism can cause gastric and duodenal ulcers?
Helicobactor pylori
What 2 broad things contribute to ulcers?
Increase in acidity
Decrease in protective factors
How does H Pylori contribute to ulcers?
Inhibits somatostain so Gastrin is highly active.
Gastrin binds to parietal and ECL cells to increase acidity!
What does Achlorhydria mean?
Reduced acid secretion
What secretes trefoil factors that can lead to regeneration of epithelial layer?
Surface mucous cells!
What does Gastroferrin do?
Aids in Ferrous (Fe++) iron absorption
Where are chief cells?
In the body by the parietal cells
What is secreted when there is increased H+ ions, fats, and peptides in the duodenum?
What does this do to parietal HCl secretion?
Enterogastrones are secreted (CCK, secretin etc.)
They inhibit ECL cell release of Histamine so the Histamine can’t bind parietal cells…therefore there is a decrease in acid secretion
When is pepsinogen secreted?
In response to ACh and gastrin
What inhibits pepsinogen release?
Secretin
What is meant by the term “autoactivation” in terms of pepsinogen?
Once pepsinogen hits the acidic environment of the stomach…it is cleaved into pepsin which is a POTENT PROTEOLYTIC ENZYME!
Besides pepsinogen, what else do chief cells secrete?
Lipase!
Surface epithelial cells secrete mucus and bicarbonate in response to what?
PGE2
How do NSAIDs lead to gastric irritation?
They block the production of PGE2…therefore there is reduced mucus secretion…this contributes to gastric irritation
How do catecholamines contribute to stress ulcers?
Catecholamines suppress mucosal BICARBONATE secretion…this contributes to gastric irritation and the formation of stress ulcers
What are the 4 phases of digestion?
Interdigestive
Cephalic
Gastric
Intestinal
If peptic ulcer disease is caused by H pylori, what two things are you going to use to tx?
Antibiotic
PPI
How may H pylori contribute to an increase in acid production?
Urease may inhibit somatostatin…this lets Gastrin go wild to act on parietal and ECL cells
What 2 ways do NSAIDs contribute to ulcer formation?
No prostaglandins!
Normally PGE2 contributes to mucus formation…without it we have less mucus.
Without prostaglandins we have tons of histamine release so there is a ton of acid production.
What are foveolar cells?
Epithelial cells that secrete mucin.
How may H pylori contribute to ulcers?
H pylori has urease which makes the environment more basic. This inhibits somatostatin. We, therefore, have no inhibition of gastrin so a crap ton of gastrin is secreted and we get lots of acid production!
