gastric secretion - the cephalic and gastric phase Flashcards
what stimulates the cephalic phase?
sight of food
thought of food
smell of food
taste of food
how do stimulators of the cephalic phase cause gastric secretions?
cause stimulation of cerebral cortex
send information to the hypothalamus
send descending axons to the dorsal nucleus of vagus in the medulla
vagus nerve goes to all parts of the stomach - to parietal and chief cells to make HCl and pepsinogen, which forms pepsin in certain pH
what inhibits cephalic gastric secretions?
anything that activates the sympathetic nervous system
e.g. stress, emotional upset
how do factors that inhibit the sympathetic nervous system inhibit cephalic gastric secretions?
pre-ganglionic fibres form the splanchic nerve, which comes to inhibit secretions from the stomach to decrease HCl and pepsinogen production
what happens to chief cells when gastrin is secreted?
has CCK-1 receptors on chief cells, stimulate an increase in Ca, stimulates vesicles to fuse with membrane to release pepsinogen, high proton concentration converts it to pepsin, its active form
what happens to parietal cells upon the release of gastrin?
proteins in the mucosa can stimulate G-cells so secrete gastrin, which acts on CCK-2 receptors on parietal cells to release Ca into the cell, which stimulates proton pumps to pump out protons
what stimulates gastric secretions?
distension (stretch)
partially digested proteins (pH)
inhibitors of gastric secretions
SNS
somatostatin (stimulis is very low pH)
when is somatostatin secreted
in response to low pH by antral D-cells
how does somatostatin inhibit gastrin
somatostatin leaves the blood and acts on paracrine somatostatin receptors, inhibiting G-cells from releasing gastrin
how can the vagus nerve act on antral D- cells and G-cells
releases acetylcholine, inhibiting D-cells from releasing somatostatin
gastrin can also inhibit D-cells from releasing somatostatin
acetylcholine can stimulate gastrin secretion from G-cells
somatostatins effect on parietal cells
acts on SST receptors
activates Gi pathway to directly inhibit proton pumps
acetylcholines effect on parietal cells
binds to M3 receptors
stimulate an increase in Ca levels
stimulates the proton pump
histamines effect on parietal cells
binds to H2 receptors
acts through Gs pathway
stimulates proton secretion
prostaglandins (PGE2) effect on parietal cells
binds to EP3 receptors
acts through Gi pathway
inhibit hydrochloride acid secretion
