L7 - Carriage of Carbon Dioxide

How much % is transported in each part of the blood?

• 5% dissolved Plasma

• 10-20% bound to haemoglobin

• 75-85% converted to hydrogen carbonate ions in Cytoplasm

Where is Carbaminohaemoglobin formed/broken down?

Tissues:

Hb + CO₂ → HbCO₂

Lungs:

Hb + CO₂ ← HbCO₂

How does CO₂ bind?

It binds to a different site in Hb than O₂ but changes shape of protein so less O₂ can bind to Hb.

• If HIGH CO₂ and low pH —> CO₂ binds + CO₂ released

• If LOW CO₂ and high pH —> CO₂ binds + CO₂ binds

What is the effect of CO₂ on dissociation?

In presence of MORE CO_2<

More H₂CO₂ produced

More H⁺ produced

• binds to Hb

• affects quaternary structure, lowers affinity for O₂

increases competition for Hb

Less O₂ binds, more released

What is the Bohr effect?

In ACTIVE tissues pCO₂ is high

Causes right shift in oxygen diss. curve

Means HB releases O₂ more easily

What is the cycle of Hydrogen Carbonate ions and Hydrogencarbonate ions?

• CO₂ and H₂O forms carbonic acid (H₂CO₃)

  • Via Carbonic Anhydrase catalyst

• Once Carbonic acid formed, dissociates releasing H⁺ ions and Hydrogencarbonate ions - decreases pH of blood

• Chloride shift occurs to balance electrical balance of cell

• H⁺ ions accepted by Hb to form Haemoglobinic acid

  • Acts as a buffer to prevent pH from decreasing

• Hydrogen carbonate ions and hydrogen ions then combine to reform carbonic acid

• Carbonic acid forms back into CO₂ to be diffused to alveoli out of lungs to be exhaled.

What is the chloride shift?

• Negative charged Hydrogen Carbonate ions (HCO₃^-) diffuse out down conc. gradient leaving a + chage

• To balance electrical balance of cell, Chloride ions move into erythrocyte (RBC)