Pharmacology of gastric secretion Flashcards
What do mucus cells secrete?
Mucous and bicarbonate
What do parietal cells secret?
HCL
What do enterochramaffin-like cells secrete?
Histamine
What do G cells secret?
Gastrin
What do D cells secret?
Somatostatin
Action of histamine?
- Secreted by enterochromaffin-like cells in gastric glands in response to stimulation by Ach
- Histamine binds to H2 receptors with subsequent activation of adenylyl cyclase
- Increase in cAMP increases number of proton pumps increasing gastric acid secretion from parietal cells
What is histamine secreted by? And why?
Enterochromaffin-like cells in gastric glands in response to stimulation by ACh
What does histamine bind to?
H2 receptors with subsequent activation of adenylyl cyclase- this increases no. of proton pumps, increasing gastric acid secretion from parietal cells
What is ACh released by?
Parasympathetic cholinergic neurons
What does ACh bind to?
Muscarinic M3 ACh receptors on parietal cells with subsequent activation of PLC (phopsholipase?)- The increase in extracellular Ca2+ evokes cell signalling pathways that increase the no. of proton pumps, increasing gastric acid secretion from parietal cells
What is gastrin released by?
G cells
What does gastrin bind to?
CCK2 receptors on parietal cells with subsequent activation if PLC
-Increase in extracellular Ca+ increases the no. of proton pumps, increasing gastric acid secretion from parietal cells
What secretes somatostatin?
Secreted by D cells in gastric glands
What does somatostatin bind to?
SST2 receptors inhibiting adenylyl cyclase, decrease in cAMP results in decreased gastric acid secretion from parietal cells
What is the result of somatostatin binding to SST2R receptors or enterochromaffin-like cells?
Reduced histamine release and decreased gastric acid secretion from parietal cells
What is the action of NSAIDs?
Disrupts the production of prostaglandins by inhibiting COX-1
What effect does NSAIDS action have?
Reduced availability of prostaglandins results in histamine secretion from enter-chromaffin like cells= promoting HCL secretion from parietal cells
Example of an NSAIDs?
Aspirin
Diverse affects of NSAIDs and what can help them?
Peptic ulcers
Misoprostol (analogue of prostaglandin E1)
Side effects= abdominal pain and diarrhoea, also induces labour
Side effects of misoprostol?
Abdominal pain and diarrhoea
Induces labour
-Helps peptic ulcers
Examples of Proton pump inhibitors?(PPIs)
Lanzoprazole
Omeprazole
Pantoprazole
What do PPIs do?
Irreversibly inhibit H+/K+ ATPase- reduces HCL secretion
What are PPIs indicated for?
Benign gastric peptic ulceration and NSAID- associated gastric ulceration
Gastro-oesphageal reflux
Zollinger-Ellison syndrome
Side effects of PPI?
Inreased stomach pH reduces defences against GI tract infections
Examples of Histamine H2 receptors agonists?
Ranitidine
Cimetidine
Famotidine
Nizatidine
Action of Histamine H2 receptors agonists?
Blocking H2 receptor eventually reduces HCL secretion, complete block of it produces rapid effect
What are histamine H2 receptors indicated for?
Benign gastric acid ulceration
NSAIDs associated gastric ulceration
What can cause peptic ulcers (bacteria)?
H. Pylori
Causes persistent inflammation that weakens mucosal barrier, eventually exposing sub-mucosa to attack from HCL and pepsin
How to get rid of H. Pylori?
PPIs & antibiotics (clarithromycin & amoxicillan or metronidazole)
