Questions bout the Chloride Shift in R.B.cell

[crays]

Hi, i have a question bout the chloride shift that occurs in the red blood cell. After the carbon dioxide has dissociated into the Red Blood Cell's plasma and became H⁺ and HCO₃^- i would like to know why must the HCO₃^- must go out and combine with the Sodium ions and since the H⁺ ions have combined with Hemoglobin, Hb. Why is Cl^- still needed and shifted into the Red Blood Cell? Doesn't H.Hb is already neutralized?

Sorry if you think this is a very easy question, but my book just told me there is a chloride shift, there is no explanation given on the mechanism. Thanks.

 

[chound]

A wild guess:
Maybe there's not much space for all that HCO3- in the RBC, its m.wt. being 61 and for Cl- it is 35 ?

A better guess I think would be the altered pH of the RBC cytosol due to HCO3- accumulating in it causes it to become more basic?
Maybe the HCO3- may try to displace the H+ from H.Hb hence it has to be transported out?

Cl- is anyway needed for the maintenance of the osmolarity