Transport of Carbon Dioxide

Why must Co2 be removed from the blood

• forms an acid which changes the blood pH - fatal

3 ways in which Co2 is carried in the blood

• dissolved in plasma

• bound to amino groups on the polypeptides of Hb

• chemically modified in the erythrocyte

Describe how Co2 is chemically modified in the erythrocyte

• Co2 diffuses into rbc

• carbonic anhydrase catalyzes the reaction with water

• forms Carbonic acid H2CO3

• dissociates into HCO3- and H+

• H+ displaces o2 and binds to hb forming hemoglobinic acid

Chloride Shift

• Hco3- moves out of rbc by a transporter

• exchanges 1 cl- for hco3-

Summary Description of Carbon Dioxide Removal from Tissues

• co2 diffuses in plasma

• co2 diffuses in rbc and reacts with water and through enzyme carbonic anhydrase forms H2CO3

• H2co3 dissasociates into Hco3- and h+

• higher affinity for H+ due to low o2 conc so more unloading of o2 and h+ is taken up

• this avoids ph from changing

Brief description of carbon dioxide release in the lungs

• CO2 diffuses out of the plasma and into the alveoli

• Higher PO2 means that Hb’s affinity for oxygen increases displacing the H+

• HCo3- comes back into the cell through a reverse chloride shift and reacts with the H+ to form H2co3

• h2co3, through carbonic anhydrase the reaction is reversed into co2 and h2o

Effects of CO

• oxidizes Fe2+ → fe3+

• binds to Hb than o2, and forms a stable compound carboxyhemoglobin

• no o2 released to cells - DEADLY

Effects of Nitric Oxide

• vessel dilation

• smooth vessel relaxation