L11 Flashcards
what do GI tract hormones and nerves signals promote
secretion of fluids and enzymes from epithelia and other associated organs
parietal epithelial secrete what
acidic fluid into the stomach
what does the pancreas secrete
digestive enzymes from the acinar cells
bicarbonate rich fluid from the duct cells
what cells would you find in the stomach
mucus cells
parietal cells
enterochromaffin like cells
G cells
D cells
what is the role of the different cells in the stomach
mucus cells - protection
parietal cells - secrete acid
enterochromaffin like cells - activate the parietal cells
don’t need to know what the G cells and D cells do
what are the advantages of multiple signals, using different pathways, stimulating the same physiological outcome
We have 2 (there’s more than 2 but we only learn 2) different pathways so that we get more acid secreted. and if one isn’t working then we still get acid secreted
how is histamine released
the vagal nerve (in the brain stem) stimulates the enteric nerve which stimulates endochromiffin like cells (ECL cells)
where is histamine released from
ECL cells
what is the histamine signal transduction pathway
not the pathway of histamine release but the pathway that histamine causes
vagal nerve stimulates enteric nerve which stimulates ECL cells
ECL cells release histamine
it binds to the H2 receptor (which is GPCR)
adenylyl cyclase catalyzes ATP –> cAMP which activates PKA
PKA phosphorylates the H/K pump which causes it to be endocytosed into the apical membrane
H+ is pumped out of the cell as well as Cl through CFTR to create HCL in the stomach
describe the ACh signal transduction pathway
the vagal nerve stimulates the enteric nerve which releases ACh
ACh binds to the M3 receptor (muscarinic receptor) which is a GPCR. this convertes GTP –> GDP
this activates phospholipase C which breaks down PIP2 into IP3 and DAG
DAG activates PKC
IP3 binds to its receptor on the ER. increased cytoplasmic Ca levels
together this leads to the phosphorylation and activation of the H/K pump causing to it be exocytosed to the apical membrane causing HCL to be secreted into the lumen of the stomach
what happens when something in the acid production pathway don’t go right
acid reflux, gastric ulcers and gastric cancer
what is used to treat acid reflux
proton pump inhibitors
these bind to the H/K ATPase
what is helicobacter pylori
it is a bacteria which inhibits acid secretion and promotes gastric ulcer formation eventually leading to gastric cancer
how does helicobacter pylori cause ulcers and cancer
damages the epithelial meaning that the acid is able to leak through the epithelium leading to gastric ulcers and stomach cancer
For successful stimulation of hydrochloric acid secretion from stomach parietal epithelial cells:
A. Histamine is released from enterochromaffin-like (ECL) cells.
B. Histamine stimulates conversion of phosphatidyl inositol bisphosphate (PIP2) to diacylglycerol (DAG) and inositol triphosphate (IP3).
C. Histamine activates a GPCR, while acetylcholine does not
D. Vesicular H+/K+ATPase is endocytosed from the apical
membrane
A. Histamine is released from enterochromaffin-like (ECL) cells.
B is right but for ACH not histamine
D should say exo
what do acinar cells secrete
digestive enzymes
what are acinar cells stimulated by
CCK
what do ductal cells secrete
bicarbonate rich fluid in response to secretin
what stimulates ductal cells
secreatin
what is pancreatic secretion important for
Important for regulating sugar levels but it is also important for digestion
what stimulates the release of CCK
fatty acids in digested food when it is passes into the intestine
where is CCk released from
I cells in the small intestine
how does CCK stimulate exocytosis of digestive enzymes
signal transduction pathway
CCK binds to its CCK1 receptor on the basolateral membrane of the pancreatic acinar cells
this is a GPCR which activates PLC
PLC breaks down PIP2 into IP3 and DAG
IP3 and DAG do their thang which leads to the exocytosis of zymogen granules
what are zymogen granules
These are vesicles that digestive enzymes are in.
They are in special things so they don’t start digesting the inside of the cell
what causes secreatin to be released from intestinal cells
a decrease in pH in the duodenum
what cells release secretin
intestinal S cells
what is the signal transduction pathway for secreatin
it binds to it S1 receptor on the pancreatic membrane of the ductal cells
this is a GPCR therefore it activates adenylyl cyclase which breaks down ATP –> cAMP
cAMP activates PKA which phosphorylates CFTR
CFTR is then exocytose into the apical membrane of the pancreatic ductal cells
what does CFTR do in the ductal cell
it pumps out bicarbonate to neutralize the acid as it comes passed. it also acts as a carrier for the digestive enzymes to help them get the the small intestine
when does cystic fibrosis happen (in terms of its effect on the digestive system)
when the bicarbonate rich fluid is absent or reduced
this happens when CFTR is absent or dysfunctional
what happens when you get reduced bicarbonate rich fluid
reduced fluid in the duct means that you are unable to move those digestive enzymes down the pancreatic duct (no digestion = malnourished)
it also means that there will be no neutralisation of the small intestine (stomach ulcers which then could progress into stomach cancer)
