-a wild hormone appears!-
for fun’s sake, let’s call this one histamine. this is histamine’s mechanism of action at stomach parietal cells.
– – – – – – – – – – – – – – – -[membrane receptor]- – – – – – – – – – – – – – –
* adenylate cyclase:
(an enzyme) associated with the receptor;
when a ligand (histamine) binds to the receptor on the surface of the cell membrane,
adenylate cyclase (on the inside of the membrane) is activated.
:ATP is converted to cAMP.:
– ATP is the cellular energy unit; the reason we eat food is so that cells can turn it into ATP. it has a variety of uses. this is one of them.
– cyclic AMP is what we can a secondary messenger, the extracellular hormone being the primary. as its #s increase within the cytoplasm, stuff happens…
cAMP has different effects at different cells! it can promote protein activation; [it turns on “cAMP-activated ports”: luminal membrane anion channels that allow ions to leave the cell], as well as protein synthesis [such as that of the H+/K+ ATPase used by parietal cells to spit acid into the tummy lumen]. In order to move synthesized proteins to the cell membrane, which is where they usually need to go to do useful protein stuff, we need to raise intracellular [Ca++].
-a wild hormone appears!-
at parietal cells, this one could be Ach (not a hormone but a neurotransmitter) or gastrin.
– – – – – – – – – – – – – – – -[a different membrane receptor]- – – – – – – – – – – – – – –
* Phospholipase C
:PIP is converted to IP3:
IP3 is a secondary messenger that stimulates the endoplasmic reticulum to release its calcium!
Intracellular [Ca++] increases
Ca++ is necessary for exocyosis of vesicles, lil bubbles within the cell bubble; made of the same bilipid membrane and usually holding some treasure inside.
In this case a vesicle containing H+/K+ ATPase (a membrane transport protein) is formed at the Golgi and moved to the membrane.
It fuses with the luminal bilipid membrane and thusly adds a shiny new H+/K+ ATPase, which spits H+ out into the stomach lumen in exchange for K+.
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i used to hate this stuff but now that i know where it fits in the big machine i think it’s pretty great. great job darwin!
doctorbotson 