CO2 transport Flashcards
How is CO2 transported + %?
carbaminohaemoglobin 70%
dissolved within the plasma 7%
converted to HCO3⁻ 23%
Why’s more CO2 carried in plasma than O2?
CO2 is more soluble than O2
5.3 vs. 0.2 mL/L/kPa
Why’s less CO2 transported w Hb?
CO2 binds to Hb at diff sites, R-NH2 residues form carbaminohaemoglobin R-NHCOOH w decreased affinity
Why’s CO2 converted to HCO3⁻?
CO2 dissolves in H2O to form carbonic acid
CO2 + H2O -> H2CO3
H2CO3 -> H⁺ + HCO3⁻
What’s carbonic anhydrase?
enzyme expressed in high conc w 🔴, catalyses CO2 + H2O reaction
How levels of CO2 affect amount of O2 carried by Hb?
Increased CO2 decrease affinity + decrease amount of O2 bound to Hb at given PO2
How does CO2 reduces O2 affinity to Hb?
CO2 + H⁺ bind to Hb inducing conformation change, which changes O2 binding site
Define Haldane effect
oxygenated blood has reduced affinity for CO2 so venous blood carries more CO2
Why the CO2 carried by venous blood increases?
- H⁺-Hb binding acts as buffer by removing H+ from surrounding environment
- eq shift to right
- dissolved CO2 pulled out of plasma into storage as HCO3⁻
- lost CO2 replaces by fresh CO2
Summary of what happens at tissues
- CO2 produced by tissues, dissolves in plasma
- enters 🔴
- CO2 + H2O -> H2CO3
- removal of CO2 enables more CO2 to diffuse into 🔴 (then more can enter plasma)
- H2CO3 ionises -> HCO3-+H⁺
- 🔴 membrane impermeable to H⁺ so can’t leave
- H+ accumulates
- H⁺ -Hb acts as buffer
- movement of O2 into tissues ∴ ↑[deoxy-Hb]
- more CO2 transport
- increased [HCO3-] creates diffusion gradient for HCO3- to leave cell
- exchanged for Cl- to maintain electrical neutrality
Summary of what happens at lungs
- Low PACO2, creates a diffusion gradient for CO2 to diffuse out blood
- Increased PAO2 –> O2-Hb binding
- O2-Hb binds less H⁺
- increasing free [H+] –>increased H2CO3 + CO2
- CO2 moves into plasma
- changing eq –> decreased [HCO3-] (as it binds free H⁺) -diffusion gradient allows HCO3- ions enter🔴in exchange for Cl-.
oxygenation of blood enables greater CO2 release- Haldane effect
How acidosis occurs?
If excess dissolved CO2 cannot be released then oxygenation of blood enables less CO2 to be transported –> CO2 accumulation
Why starting supplemental O2 therapy rapidly in patients with severe COPD dangerous?
- oxygenation of their blood enables it to carry less CO2 due to Haldane effect
- COPD patients chronically hypoventilate their lungs so CO2 accumulates + blood carries more CO2 due less O2 (they’re hypercapnic + hypoxaemic)
- w O2 therapy, CO2 displaced from blood
- blood carries less CO2-Hb + HCO3⁻
- more CO2 withinbody –> dangerous acidaemia
How does healthy individual react to supplemental O2 therapy?
hyperventilates to remove excess CO2
COPD patient can’t due to hypoventilation + deterioration in lung
How does inert gas narcosis occur?
pp of gases can increase within blood that produce intoxicating effect at very high p :low underwater
depth during extreme diving
