Physiology and Pharmacology - Gastric Gland Secretions Flashcards
What type of cells are present in the pyloric gland area (antrum)? (2)
D cellsG cells
What type of cells are present in the oxyntic mucosa in fundus and body of the stomach? (3)
Chief cellEnterochromaffin-like cellParietal cells
What do D cells secrete?
Somatostatin
What do G cells secrete?
Gastrin
What do chief cells secrete?
Pepsinogen
What do enterochromaffin-like cells secrete?
Histamine
What do parietal cells secrete?
Hydrocholric acidIntrinsic factor
What does pepsinogen released from chief cells do?
Precursor of pepsin which when activated by HCl becomes pepsin
What does histamine released from enterochromaffin-like cells do?
Stimulates HCl secretion
What does hydrochloric acid secreted from parietal cells do?
Activates pepsinogen to pepsinDenatures proteinKills most micro-organisms ingested
What does intrinsic factor released from parietal cells do?
Binds vitamin B12 allowing adsorption in the terminal ileum
What does somatostatin released from D cells do?
Inhibits HCl secretion
What does gastrin released from G cells do?
Stimulates secretion of HCl acid
What is the full name of the proton pump?
H+/K+ATPase (pumps H+ out and K+ in)
Where does the Cl- come from that makes HCl?
It is pumped into the cell via the Cl-/HCO3- antiporter and is then pumped into the caniliculis via a Cl- channel
What 3 regulatory molecules stimulate HCl secretion?
AChHistamine Gastrin
What receptor does ACh stimulate acid secretion via?
M3
How does ACh stimulate secretion of HCl?
When M3 is activated, it stimulates the proton pump and hence secretion of H+It also acts on M1 receptors on Enterochromafin like cells causing the release of histamine
How does histamine stimulate secretion of HCl?
It acts on an H2 receptor on the membrane of parietal cells increasing the activation of the proton pump
How does gastrin increase secretion of HCl?
It stimulates gastrin receptors which increase activation of the proton pumpGastrin also stimulates ECL cells increasing histamine release
What inhibits HCl release? How?
Somatostain inhibits the release of gastrin and histamineProstoglandin E2 stimulates prostoglandin receptors on parietal cells inhibiting the action of ACh, gastrin and histamine
What is a secretagogue?
A substance that causes another substance to be secreted
How are proton pumps activated? e.g. by histamine, ACh and gastrin
Causes the insertion of the proton pump into the apical membrane - through protein kinases
What are the 3 phases of gastric secretion?
Cephalic (before food reaches the stomach)Gastric (when food is in the stomach)Intestinal (after food has left the stomach)
What happens during the intestinal stage of gastric secretion?
Factors originating from the small intestine switch off acid secretion
What effects do prostaglandins have locally in the stomach?
Reduce acid secretionIncrease mucus and bicarbonate secretionIncrease mucosal blood flow
What is a peptic ulcer?
An area where the mucosa is exposed to HCl and pepsin
What is Zollinger-Ellison syndrome?
Rare, gastrin producing tumour
