Week 3 - Gas Exchange Flashcards
What effect does SVP have on pO2 in inhaled air?
-Decreases it
What is fick’s first law of diffusion?
-diffusion is proportional to permeability of the molecules x surface area x concentation gradient
Which molecule O2 or CO2 diffuses more quickly through air? why?
-O2 because it is smaller
What is diffusion rate dependant on when gases diffuse through liquids?
-Solubulity
In blood, which molecule CO2 or O2 diffuses more quickly? Why?
-CO2 as even though it is bigger it is much more soluble
If O2 is poorly soluble, what drives O2 gas exchange?
-The large concentration gradient of oxygen drives diffusion
Why is O2 diffusion more effected than CO2 diffusion in a diseased lung?
-CO2 is much more soluble than O2
What is the pO2 and PCO2 in the following areas:
i) tracheal air
ii) alveolar air
- i)pO2 -> 19.6% pCO2->0.04%
- ii) pO2 -> 13.3% pCO2 -> 5.3%
What is the rate of diffusion dependant upon in the lungs?
- Surface area
- Diffusion resistance (barrier)
- Concentration gradient
Why is pO2 lower in alveoli compared to external environment?
- Continuous diffusion across alveoli
- Diluting effect of CO2
What happens to CO2 which enters RBC as waste?
- Combines with H2O to produce carbonic acid
- CA dissociates into HCO3 and H+
- HCO3 enters plasma whilst H+ are buffered by Hb inside rbc
How is CO2 carried in the blood?
- 5% dissolves in plasma
- 5% are carboxyhb on proteins
- 90% as bicarb
Why is it okay to have a shallow pCO2 gradient between blood and alveoli?
-High solubility means it diffuses easily despite gradient
Describe pO2 and pCO2 in arterial and venous blood
- arterial = pO2->13.3kPa pCO2-> 5.1kPa
- Venous = pO2 -> 5.3kPa pCO2-> 6.1kPa
What determines diffusion resistance?
- Nature of barrier (pathlength and permeability)
- Nature of molecule
