CO2 Transport

Question 1

Forms of CO2 in the blood

Answer 1

• Produced in the tissue and carried to the lungs in venous blood
• Dissolved CO2 free in solution
• Carbaminohemoglobin is bound to Hb
• Bicarbonate (HCO3-) from hydration of CO2 in RBCs
  
  • H2O+CO2H2CO3HCO3- + H+
  • Major Form

Question 2

Transport of CO2 as HCO3-

Answer 2

• CO2 generated in the tissues and diffuses into venous blood
• In RBC, CO2+H2O forms H2CO3
  
  • catalyzed by carbonic anhydrase
  • H2CO3 dissociates to HCO3- and H+
• HCO3- leaves RBC in exchange for Cl-
  
  • Chloride shift
  • HCO3- is major form of CO2 transported to lungs
• H+ buffered in RBC by deoxy-Hb
  
  • deoxy is better buffer than oxy-Hb
  • Mostly deoxy-Hb @ venous end where CO2 added
• In lungs, reaction reverses and HCO3- enters RBC for Cl-
  
  • HCO3- combo w/ H+ to form H2CO3
  • H2CO3 decomposes to H+ and CO2 and CO2 expired

Question 3

Significant differences between oxygen and carbon dioxide transport

Answer 3

• Diffusion rates, minimal pressure differences, lack of dedicated carrier for CO2
  1. solubility of the gas in fluid: CO2 much more soluble than O2
  2. difference in partial pressure between compartments: Much smaller difference than O2

Question 4

Dissolved CO2 transport

Answer 4

• solubility in plasma is 20x as compared to O2

- partial pressure difference is 5 mm Hg: 45 @ venous – 40 @ arterial

Question 5

Transport As Carbamino compounds

Answer 5

-CO2 may slowly react with proteins instead of water: no enzymatic activity
-Reaction occurs w/ amino group of plasma and RBC proteins to form carbamino compounds
-Due to the extremely high concentration of hemoglobin, most of this process occurs with this protein in RBCs.
RNH2+CO2 RNCOOH + H+

Question 6

CO2 dissociation Curve and Haldane Effect

Answer 6

-The sum of the CO2 forms in blood and the relationship to Pco2 can be depicted by a dissociation curve
-Normal range of CO2 curve function is narrow!
-Haldane Effect:
-O2 binding to Hb causes CO2 to be released from the blood more effectively.
-Oxy-Hb shifting the curve to the right doubles CO2 release from the blood at pulmonary capillaries.
-Mechanism:
1.O2 binds Hb- makes it become a stronger acid.
Released H+ binds bicarb and forms carbonic acid which dissociates into CO2 and water.
2.Oxygen binding to carbaminohemoglobin displaces the CO2 from it directly.
3.Both of these mechanisms increase CO2 release from blood to diffuse into alveolar space.