Davie RS 1- Gastric Secretions Flashcards
What is the difference in the appearance of vesicles in parietal cells before and after stimulation?
In the resting state, tubulovesicles are present: the K/H+ATPase is embedded in the membrane and not on the exterior of the cell
When stimulated, canaliculus are present: There is an enormous expansion of the membrane of the cell and the pump is now on the exterior
What molecules do parietal cells have receptors for? What protein kinases do they work through?
Parietal cells have receptors for histamine, acetylcholine and gastrin. Histamine works through PKA, while ACh and gastrin activate PKC
What is the difference between the direct and indirect pathway of parietal cell activation?
In the direct pathway, acetylcholine, histamine and gastrin directly bind to parietal cells.
In the indirect pathway, acetylcholine (released by the vagus nerve via ENS stimulation) and gastrin (binding to CCK-B receptors) cause histamine to be released from enterochromaffin like cells (ECL cells). Histamine can then bind to parietal cells
What signaling molecules are agonists of chief cells? What pathways do they work through?
Secretin, VIP, Beta-2 adrenergic agonists, and PGE-2 via EP2 receptors, all activate chief cells via adenylyl cyclase
Gastrin and acetylcholine both increase intracellular calcium levels
Where are D cells located? What do they synthesize and secrete?
D cells are found in the pancreas, small intestine, and the antrum and corpus of the stomach
They synthesize and secrete somatostatin
What are the direct and indirect pathways of somatostatin’s actions regarding acid release?
In the direct pathway, somatostatin can bind to Ga-i receptors on parietal cells and inhibit adenylyl cyclase
In the indirect pathway somatostatin inhibits histamine release from ECL cells, as well as inhibit gastrin release from G cells in the antrum
How do gastric and cholinergic agonists affect somatostatin?
Gastrin stimulates somatostatin release, while cholinergic agonists are able to overcome negative feedback and inhibit somatostatin
Where are G cells located?
Antrum and duodenum (Lower stomach)
How much of lipid digestion occurs in the stomach? How does this occur?
At most, 30% of lipid digestion occurs in the stomach.
Gastric and lingual lipases are at an optimal pH in the stomach and are responsible for gastric lipid digestion
Are prostaglandins good or bad for the mucosa? What are their negative/positive effects?
Prostaglandins are good for the mucosa. They reverse injury to it by inhibiting acid secretion, increasing mucosal blood flow and modifying the local inflammatory response induced by acid
