Lecture 11 Flashcards
In the GI tract, ______ and ________ signals promote the secretion of _______ and ______ from epithelia and associated organs
hormones
nerve
fluids
enzymes
Parietal epithelia secrete what into the stomach?
acid
What does the pancreas secrete?
digestive enzymes (from acinar cells) and bicarbonate rich fluid (from duct cells)
What are 5 cells inside the stomach?
Mucus cells Parietal cells enterochromaffin-like cell G-cell D cell
What is the purpose of the mucus cell?
to protect the other cells from the acid
What is the purpose of the parietal cell?
it secretes acid into the stomach
What is the purpose of the enterochromaffin-like cell?
these stimulate Parietal cells
What are two different ligands that are important for HCl secretion?
- ACh
- histamine
What is the advantage of having two ligands that can release HCl from the parietal cell?
- to get more acid secretion
- if one is not working, the other can take over
There are 4 steps to the histamine signal transduction pathway. What is the first one?
histamine binds to the H2 receptor in parietal cells
What happens after histamine binds to the H2 receptor in parietal cells?
This receptor is a GPCR and it dissociates and activates adenylyl cyclase to catalyse the conversion of ATP to cAMP which activates PKA. PKA phosphorylates the H+/K+ pump, promoting its exocytosis to the apical membrane. H+ is pumped out of the cell, as well as Cl- through the CFTR which causes an increase in HCl
What stimulates the release of histamine? Where is it released from?
The vagal nerve sitting in the brainstem stimulates the enteric nerve which activates ECL cells and then histamine is released from the enterochromaffin-like cells
What stimulates the release of ACh and where is it released from?
The vagal nerve sitting in the brainstem stimulates the enteric nerve which releases ACh.
What does ACh do? Where does it bind? What does this cause?
ACh binds to the M3 receptor which is a GPCR, there is the conversion of GDP to GTP and the activation of PLC. PLC breaks down PIP2 to IP3 and DAG. DAG activates PKC and IP3 binds to its receptor in the ER which leads to Ca2+ being pumped out of the ER. The combined effect of these two things leads to the activation of the H+/K+ pump which is exocytosed to the apical membrane. This allows HCL to be secreted into the lumen of the stomach
What is one way to treat acid reflux?
- through proton pump inhibitors (tablets) which bind to the H+/K+ATPase and is used to treat acid reflux