[MS] Cellular mechanisms of gastric acid secretion

Morphologically speaking within parietal cells, upon stimulation, tubovesicles by the (apical/basolateral) cytoplasm, which contain (K+/H+ or K+/Na+ ATPase channels) will become incorporated into the (apical/basolateral) membrane
Click the card to flip 👆
1 / 10
Terms in this set (10)
Morphologically speaking within parietal cells, upon stimulation, tubovesicles by the (apical/basolateral) cytoplasm, which contain (K+/H+ or K+/Na+ ATPase channels) will become incorporated into the (apical/basolateral) membrane
1. apical
2. K+/H+ ATPase
3. apical (or canalicular) membrane
Which molecules stimulate the parietal cells?
- Ach
- gastrin
- histamine
When the K+/H+ ATPase is inserted into the cannalicular membrane of the parietal cells, what changes occur?
- microvilli are produced to increase surface area
- increases proton pump on the apical membrane
Why do parietal cells have a lot of mitochondria?
they need energy to power the secretion of H+ ions which is ATP-dependent
What receptor does ACh act on?
muscarinic (M3) receptors
What receptor does gastrin act on?
CCKb gastrin receptors
What happens, in terms of intracellular messaging, within the parietal cells once ACh and gastrin bind onto their respective receptors?
1. stimulation of phospholipase C

2. IP2 is converted to IP3 & DAG

3. IP3 stimulates Ca++ release from stores

4. Ca++ activates calmodulin-dependent protein kinase

5. DAG activates protein kinase C

6. histamine's action on H2 receptors activates adenylate cyclase which increases cAMP production from ATP

7. cAMP-stimulated protein kinase A, Ca++ and protein kinase C change parietal cell function

8. events occur within cell that lead to acid secretion
How does the alkaline tide phenomena come about?
- H+ ions derived from water

- open K+ channels allow K+ diffusion into the canaliculi, so the proton pump is stimulated to hydrolyse ATP to expel H+ to draw the K+ ion back into the cell

- Cl- ions can enter the canaliculi via Cl- channels

- the OH- left from the first step reacts with CO2 in the presence of carbonic anhydrase to produce bicarbonate

- the bicarbonate is exchanged for Cl- ions in the basal membrane, the movement of bicarbonate down the electrochemical gradient drives inward transport of the Cl- ions

- bicarbonate diffuses into the blood

- produces the alkaline tide phenomena
How does the Na+/K+ ATPase work?
Transports three Na+ out of the cell for every two K+ into the cell at the expense of one ATP.
How does the sodium pump help with the generation of gastric acid (secretions)?
- due to its actions, K+ ions accumulate inside the cell and can move down the electrochem gradient through channels in the basolateral and canalicular membranes

- the Na+/H+ exchanger in the basolateral membrane moves Na+ into the cell, down the elctrochem gradient and expels H+

- the exchanger provides Na+ ions for the pump, allowing the K+ content of the cell to be maintained

- the expulsion of H+ leaves more hydroxide ions to be converted to bicarbonate

- the increased bicarbonate means more Cl- will be drawn into the cell when it is brought in as bicarbonate is expelled

- more Cl- leaves through the canalicular channel into the canaliculi, to produce HCl, which also creates an osmotic flow of water to produce the secretion