L3- Stomach secretions Flashcards
functions of the stomach
- store food
- regulates the release the contents into the duodenum
- mix the food with the gastric secretions
what is the inner lining called in stomach and in other organs
mucosa
function of mucous neck cell
- mucous neck cell- produces mucous and bicarbonate fluid to protect from injury and acid erosion
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function of parietal cell
secretes acid and intrinsic factor ( for absorbing food)
-predominantly found in the corupus region
function of chief cell
secretes pepsinogen whhich is a precursor for pepsin
- predominantly found in the corupus region
function of ECL like cells
secretes histamine to trigger acid secretion
- in corpus region
function of d cells
secretes somatostatin for acid secretion
-found in corupus, antrum and pylorus region of the stomach
function of G cells
secretes gastrin for acid secretion
- found in antrum and pylorus region of the stomach
what happens when a parietal cell is stimulated
- CO2 diffuses into the cell
- joins with water to make carbonic acid caytalsed by carbonic anhydrase
- the acid dissociates into H+ ion and HCO3-
- HCO3 transported out into the blood in exchange of CL- ions, resulting in alkaline tide in the plasma
- H ions transported out into the lumen in exchange for K+ ions through ATPase.
- now the acid is produced in the lumen
how does gastrin regulates acid secretion
- gastrin - stored in vesicles along the basolateral membrane of the cell and gets released through vagal stimulation
- increases expression of protom pumps in the parietal cells in the antrum
- gastrin binds to ecl cell to stimulate histamine synthesis and the histaine act upon the H2 receptors on pareital cells to release acid
what part of the nervous systems control the functions of the stomach
- ENS through vagus and sympathetic nerves
how can ACH act upon acid secretion
- stimulates parietal cells to release acid and G cells to release gastrin
- stimulates ECL cells to release histamine
- stimulates D cells to inhibit somatostatin release
– ACH stimulates G cells which then stimulates parietal cell directly and indirectly via ECL cell
triggers for acid secretion
gastrin, histamine, ACH,
inhibitory factors for acid secretion
- somatostatin
- CCK
- secretin
- VIP and GIP
how does secretin act upon the acid secretion inhibition
- inhibits gastrin release and acid secretion
- stimulated by the acid in the duodenum
how does somatostatin act upon the acid secretion inhibition
- due to high levels of gastrin in the blood, the somatostatin is released from the d cells
- inhibits gastrin from G cells and histamine secretion from ECL cells
how does VIP and GIP act upon the acid secretion inhibition
acts on the same receptors for secretin on the parietal cells to stop acid release
how does CCK act upon the acid secretion inhibition
- produced by I cells in the duodenum and jejunum in response to fat.
- reduces acid release from parietal cells by acting as an antagonist for the acid secretion
pharmacoloigcal inhibitors for acid secretion
- proton pumps inhibitors
- H2 receptors anatagonists which are competitive against histamines at the parietal cells receptors
4 phases of gastric acid secretion
-basal, cephalic, gastric, intestinal
what is basal phase
where the acid secretion follows circadian rhythm
- so its low at a.m and high at p.m
- enchanced even higher by eating
what is cephalic phase
a response to an approach of food before it reaches the mouth like by smell, sight, taste, thought.
-gastric acid and pepsinogen activated
what is gastric phase
when the food enters the stomach
- more than 50% acid secretion
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what is intestinal phase
food mixed with secretions from pancreas and liver
- gastrin secretion and gut motility inhibited
- acidic fluid in the small intestine from the stomach cause a release of secretin and other factors inhibit acid secretion
