Lecture 29 - Regulation of Gastric Acid Secretion I Flashcards
What is gastric secretion during fasting?
Close to isosmotic, high in sodium and bicarbonate coming entirely from surface cells
What is gastric secretion during feeding?
First isosmotic, low in sodium, 150mM HCl, then
hypo-osmotic due to surface processes
Secretion of bicarbonate into the stomach lumen
A. depends on a basolateral K+ gradient in parietal cells.
B. requires a basolateral Cl- gradient in surface cells.
C. changes with apical K+ conductance in parietal cells.
D. protects the surface epithelium against bacteria such as Helicobacter pylori.
C. changes with apical K+ conductance in parietal cells
When revolving door occurs, insertion of apical K+ channels when active, not there when inactive
How are the parietal cells stimulated?
Peripheral regulation
What are the two aspects of regulation of acid secretion?
Turn on (activation) and turn off (feedback regulation)
Coordination with the arrival of food
What is parietal secretion stimulated by?
ACh (neurocrine)
- postganglionic fibres in ENS
Gastrin (endocrine)
- G cells located in the antral regions
Histamine (paracrine)
- ECL cells located in the vicinity of the parietal cells
What cell is critical in the regulation of acid secretion of the parietal cells in the body or corpus of stomach?
ECL cells
Where and when is ACh released in gastric acid secretion?
Released by postganglionic neurones of ENS in response to:
- vagal stimulation involving external reflex
- local enteric nervous system reflex
What is the effect of ACh on parietal cells?
Stimulation
Directly via M3 receptors
- increase in [Ca2+]i
Indirectly via ECL cells and histamine
- main effect
Where and when is gastrin released in Gastric acid secretion?
Produced by G cells in the antrum in response to products of protein digestion
Stimulated by enteric neurones
- GRP (gastrin releasing peptide)
As a true hormone is secreted into the blood
What is the effect of gastrin on parietal cells?
Stimulates acid secretion
Directly (CCKB receptor on parietal cells)
Indirectly via ECL cells and histamine
- main effect
Intracellular second messenger of gastrin in parietal cell
- increase in [Ca2+]i
What is the most potent stimulus for gastric acid secretion?
Histamine
What does histamine operate via?
H2 receptors
What is cimetidine?
H2 blocker drug
What is the intracellular second messenger of histamine?
cAMP - PKA
