Gastric Secretion Flashcards
What does the body of the stomach produce?
Mucus
HCL
Pepsinogen
Intrinsic factor
What is the antrum responsible for?
Mixing/grinding
Gastrin produciton
Describe the wall of the fundus
Thin and stretchy
What are the three main parts of the gastric glands?
Mucous neck cells
Parietal cells
Chief cells
What do mucous cells secrete?
Mucus
What do parietal cells produce?
HCL
Intrinsic factor
What do chief cells produce
Pepsinogens
How are hydrogen ions expelled from gastric cells?
CO2 enters the cell and combines with water to form carbonic acid - this dossocaites to form carbonate and Hydrogen ion.
Carbonate leaves the cell by chloride shift
Hydrogen leaves the cell by a potassium coupled carrier (1 hydrogen out, 1 potassium in)
H20 moves as a result of the high osmolarity in the stomach lumen
Where is gastrin secreted and where is the receptor?
Gastrin secreted from the antrum, receptor is on the basolateral membrane of the body of the stomach - results in increased activity of the hydrogen - potassium carrier
Gastrin increases intracellular calcium (activating protein kinase C)
Which other compunds result in an increased activity of the potassium hydrogen carrier?
Histamine and acetycholine
What is the effect of prostaglandins?
Activate the inhibatory G protein, which results in inhibition of the hydrogen - potassium carrier
What are the three mechanisms that control gastric secretion?
Neurocrine (Vagus/local reflexes)
Endocrine (gastrin)
Paracrine (histamine)
How are paracrine hormones spread?
Interstitial pathway
What is the result of the sight, smell and taste of food on vagal tone?
Vagal tone increases
What is the result of increased vagal tone on acetylcholine and gastrin?
Increases acetylcholine production and causes an increase in Gastrin produciton by G cells
How do ECL (enterochromaffin like cells) respond to the increase in Gastrin and Acetycholine?
Release histamine
Which cells do acetycholine, gastrin and histamine act on?
Parietal cells
How is the vagal/ enteric reflex activated in the gastric phase?
Distension of stomach and arrival of food
What activates the g cells and causes the resultant increase in gastrin in the gastric phase?
Peptides in lumen
In the gastric phase what causes the ECL cells to release histamine?
Gastrin/ACh
What inhibits gastric secretion in the cephalic phase?
Stopping eating - reduces vagal activity
How is gastric acid secretion reduced in the gastric phase?
A falling pH reduces Gastrin production
What is the effect of acid in the duodenum in the intestinal phase?
Activates the enterogastric reflex
Secretin is released - reduces the secretion of gastrin and reduces the effectiveness of gastrin on the parietal cells
(Secretin also makes the pancreas and liver produce bicarbonate)
What is the result of fat in the duodenum in the intestinal phase?
GIP release - reduces gastrin secretion - resultant decrease on HCL production by the parietal cells
Summary of inhibition of gastric acid secretion
What are enterogastrones?
Hormones released from gland cells in the duodenal mucosa
Give exmamples of enterogastrones
•secretin, cholecystokinin (CCK), GIP (gastro inhibitory peptide)
When are enterogastrones released?
In response to acid, hypertonic solutions, monoglycerides or fatty acids in the duodenum
What is the effect of enterogastrones?
- Act collectively to prevent further acid build up in duodenum
- Two strategies:
- inhibit gastric acid secretion
- reduce gastric emptying (inhibit motility/contract pyloric sphincter)
Define zymogen
Inactive precursor
•Zymogen storage prevents cellular digestion
What inactivates pepsins?
Neutral pH
Pepsin is liberated by low pH – acid hydrolysis
What is the control mechanism for pepsinogen release?
Mirrors the release mechanism of HCL
(released in response to ACh, Gastrin, Histamine)
What produces gastric mucus?
surface epithelial cells and mucus neck cells
What is the role of gastric mucus?
- Protects mucosal surface from mechanical injury
- Neutral pH (HCO3) - Protects against gastric acid corrosion and pepsin digestion
What produces intrinsic factor?
Parietal cells
What is intrinsic factor essential for?
Vitamin B12 absorption
Where is the intrinsic factor/vitamin B12 complex absorbed from?
The ileum
•Defect ® Pernicious Anaemia (failure of erythrocyte maturation)
