exhaust sections

ok im not 100% sure on the sections of an exhaust

heres how i thought it worked

extractors(manifold) -> uppipe -> downpipe -> cat -> midpipes -> muffler

a catback is the midpipes (or the pipes that run along the bottom of the car) and a muffler, and a turboback includes the downpipe

but now im not so sure coz it kinda sounds a little illogical, are extractors uppipes? or downpipes? i dont know lol
coz ive seen rx7 downpipes and they were really small things like 10cm long, but since its a rotary i dunno if that may even be the 'manifold'

and how come noone ever mentions replacing the extractors? every other pipe gets replaced but ive never heard of someone replacing the extractors, r they just high flowed so theres no need until ur making huge hp?

and wots the standard process of changing over pipes if ur modifying ur wrx? i would think itd b a catback/turbo back first
then the uppipe/downpipe
but is it worthwhile changing the uppipe/downpipe if all uve got is a turboback and an ecu (boosting saying 15psi)?