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Figurę 9.32 The isohydric transport of C0₂ as bicarbonate. (a) Reactions in thc red blood ccii at thc tissues. C0₂ diffuses into red blood ccii front tissues and is convcrtcd into carbonic acid by carbon anhydrasc (Eg. 9.1 l). The carbonic acid spontancously dissociates into H ’ and HC0₃' (Eg. 9.12). The proton that dissociates from carbonic acid (boldfacc II') binds to dcoxy-Hb forcing thc Oj—I Ib cqui!ibrium front oxy-hcmoglobin to dcoxy-hcmoglobin (Fq. 9.10) with thc dissociation of 0₂, which diffuses out of thc red blood celi to thc tissues. The HCOj* diffuses out of the red blood celi and is transported in plasnta to the lung (outside of celi), (b) Rcactions in the red blood at thc lcvcl of thc lung. In thc lung. the high 0₂ pressure forccs thc rcactions in thc oppositc dircction. Rcactions arc thc reverse of thosc in thc capillarics.

Figurę 9.33 Transport of C0₂ as carbamino-hemoglobin. (a) Rcactions in the red blood celi at the tissues. C0₂ diffuses into red blood celi and rcacts with thc NH₂-terminal amino group of hemoglobin chains to form carbamino-hcmoglobin (Eq. 9.13). The rcaction releases a proton (boldfacc H *), which promotes thc dissociation of 0₂ from hemoglobin. The 0₂ diffuses out of the red blood celi to the tissues. (b) Reactions in thc red blood celi at thc lcvd of thc lung. In the lung, the high 0₂ pressure forces the reactions in thc oppositc dircction leading to thc expiration of C0₂ from thc lung. Reactions arc thc revcrsc of thosc in the capillarics.

co₂

from cells of tissues

C0₂ ♦ H20

carbonic anhydrase

HCO3

pfasma

H2CO3 +    Hb(0₂)₄

HCO3 * H⁺Hb ♦    40₂ —

to cells of tissues

(b) Red Blood Celi in Capillaries of Lung

C0₂

expired Into air

HCO3

plasma

co₂ + h₂o

carbonic anhydrase

H2CO3 +    Hb(02)₄

t

- HCO3 + H*Hb +    402

o₂

from air

from cells of tissues

(a) Red Blood Celi in Capillanes of Tissues

-► CO2 ♦ HbNH₂

r

HbNH-C02^- ♦ H* + Hb(C>2)4

\

H'Hb + 402

0₂

to cells of tissues

(b) Red Blood Celi in Capillaries of Lung

C0₂ to air

C0₂ + HbNH₂

t

HbNH-C02^_ + H* + Hb(0₂)4

t

-0₂ from air

H Hb + 402