1. PHED 1 Applied Physiology Gaseous Exchange
AS PE
PHED 1
Applied Physiology
Gaseous Exchange

2. Exchange of Gases
Occurs between the air in alveoli and blood in surrounding capillaries
Occurs between the tissues/muscles of the body and the surrounding capillaries

3. Partial Pressure
A gas will exert a pressure proportional to its concentration within the whole gas
Air – Nitrogen (71%), Oxygen (21%) and CO2 (0.03%). Together they exert 760mmHg
PP of O2 is 160mmHg (0.21x760)
We need to know this as gases move from low to high pressure
If we know the partial pressure of Co2 and O2 and various places around the body it will help to explain diffusion

4. At Alveoli
Blood entering the capillaries around alveoli has a low PP of O2 (40mmHg) when compared to that of the air in the alveoli (105mmHg)
Diffusion gradient is created (65mmHg)
O2 will diffuse from alveoli to the blood in surrounding capillaries and will continue until equal
What happens to Co2?

5. Co2? Co2 in Alveoli – 40mmHg Co2 in surrounding Capillaries – 45mmHg
Diffusion gradient – 5mmHg

6. Factors that help diffusion
Alveolar membrane is very thin
Numerous Alveoli create a very large surface area
Alveoli surrounded by vast network of capillaries creating a huge surface area for gaseous exchange to take place.
Capillaries are narrower than blood cells which distorts it’s shape and increase surface area as well as slowing blood cells down.

7. Transport of Oxygen 97% carried as Haemoglobin 3% in blood plasma
Haemoglobin attracts O2 (Hb + 4O2 = HbO8)
When PP of O2 (PO2) is high (in alveolar capillaries haemoglobin readily combines with O2 until it becomes almost fully saturated (96%)
When P02 is low (capillaries at muscles) then O2 is released to used by the respiring muscles

8. Also look at page 59.
Do task 10
At low PO2 (at the muscles) the % saturation of Hb is low (20%), the remaining 76% has been released. At high PO2 (at the lungs), Hb is 96% saturated

9. Bohr Effect
During exercise dissociation of O2 occurs more readily, causing a shift of the curve to the right. This is due to:
Increase in CO2, Lactic acid
Drop in PH
Increase in temp
These factors cause oxygen to be more attractive to Hb.

10. Myoglobin Similar to Hb Much higher attractiveness to O2 than Hb
Acts as an O2 store in the muscles sasturating itself with O2 that has dissociated from Hb
Myoglobin curve will sit well to the left of Hb. So that a really low levels of PO2, Myoglobin is still well saturated

11. Extension Material A-VO2 diff and how it affects exchange
How do we transport Co2