Also, I would just like to highlight that what Darkdzn is referring to here is merely the epinephrine pathway involving a GPCR (G-Protein Coupled Receptor), this does not always occur with G-proteins: they often activate various other enzymes (not only adenylate cyclase) etc.
This discussion has become completely irrelevant to VCE, but just to preempt that there might be some disagreement about this statement I’ll jump in here. Skip this post if you’re a VCE student.
This is not the “epinephrine pathway”. Many GPCRs act via adenylate cyclase, certainly not just some adrenoceptors (receptors that respond to adrenaline). There are actually different classes of adrenoceptors, which involve different types of G-proteins.
Other ligands that operate via adenylate cyclase include:
ADH
GHRH/GHIH
TSH
CRH
ACTH
LH
FSH
Glucagon
PTH
hCG
Calcitonin
And heaps heaps more.
Another minor point: the term epinephrine is an unusual term in Australia. We use adrenaline instead.
The reason epinephrine exists is because adrenaline is a copyright term in the US, so to avoid having to acknowledge the copyright in academic works, US academics called it epinephrine. They share the same etymology ad=on, renal=kidneys. Επι/epi=on, νεφρός/nephros=kidneys...the former being in Latin, the latter in Greek.