Hemoglobin buffer system?

i'm a confused about this hemoglobin buffer system.. sorry if this is going to be a little long! i think i'm mainly confused about the basics.. i know that this system uses chloride shifts to maintain acid-base balance. but when they say "the chloride shifts in and out of cells in response to the... show more i'm a confused about this hemoglobin buffer system.. sorry if this is going to be a little long! i think i'm mainly confused about the basics..

i know that this system uses chloride shifts to maintain acid-base balance.
but when they say "the chloride shifts in and out of cells in response to the O2 level in the blood," do they mean in and out of the red blood cells? is chloride mainly found in the extracellular fluid and by extracellular fluid, are they referring to blood? and while we're at it, is intravascular fluid considered an extracellular fluid? and is RBC considered extracellular since it is present in the blood?

i know that each chloride that leaves is replaced by a bicarbonate and for each chloride that enters, a bicarbonate leaves. but i guess my question is where and how is that related to the big picture?

here's how i currently see it or maybe how i'm trying to make sense of it but i'm not sure:
the bicarbonate (HCO3-) leaves the RBC and goes to the extracellular fluid (???).
it attracts a hydrogen ion and so it becomes a carbonic acid (H2CO3). and then it enters the RBC (???) and is released as CO2 (+H20).
i don't get where the chloride part is.. sorry if my question is confusing. as you can tell, i'm really confused.. pls help

-kristina
Update: NOBLE: i'm not really sure how to comment on my question so i'm just going to "add details." first off, thaaaaank you!!! i think i finally get it. but here's my answer to your follow up question just to make sure. "Based on chloride levels, how can I know if I got a plasma from... show more NOBLE: i'm not really sure how to comment on my question so i'm just going to "add details."
first off, thaaaaank you!!! i think i finally get it. but here's my answer to your follow up question just to make sure.

"Based on chloride levels, how can I know if I got a plasma from venous blood or arterial blood."

i don't really know the normals or the values for chloride levels but there would be a higher level of chloride in the plasma from arterial blood because the RBC is still carrying O2 (versus CO2). meaning there would be no dumping of CO2 in the blood which would've combined with H2O in the RBC to become H2CO3 which would have become a bicarb that would normally (or at least prefer to) stay in the plasma.
since the RBC doesn't lose a -charge, there is no need for the Cl- to go in which means that it would still be in the plasma. thus, a higher level of Cl- in the arterial plasma versus the venous.

did i make sense? and did i get your point??
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