1. 8.3 GAS EXCHANGE AND TRANSPORT

2. Dalton’s Law of Partial Pressure
 each gas exerts own pressure
Atm. pressure is 101 kPa, partial prsr of O2 can be calculated based on 21% in air exerts 21 kPa in the body
CO2 which is 0.03% of air only exerts kPa
gases diffuse from high partial prsr to area low partial prsr

3. Pressure Comparison of O2
Highest partial prsr of O2 is in atm, O2 diffuses from air to alveoli (21kPa in atm to 13.3kPa in blood)
largest partial prsr of O2 is arteries to capillaries (12.6 kPa to 5.3kPa)
The difference in prsr causes the movement of gases!

4. Pressure Comparison of CO2
CO2 opposite partial prsr highest in tissue & veins
N2 partial pressures remains constant not involved in cellular respiration

5. Partial pressure of oxygen lowest in veins and tissues but highest in air, this is opposite for carbon dioxide (pg. 291)

6. Oxygen Transport
O2 moves from atm, area of high partial pressure to alveoli where it diffuses into blood & dissolves in plasma
O2 doesn’t dissolve in blood well
(0.3mL O2 per 100 mL of blood)
hemoglobin increases O2 capacity, by forming a weak bond with O2 forming oxyhemoglobin

7. Oxygen Transport cont
oxyhemoglobin allowing other O2 to dissolve in plasma, so that 20 mL of O2 is found for every 100 mL of blood (70 fold increase)
amount of O2 combining with hemoglobin depends on pressure
blood entering capillaries partial pressure drops to 5.3 kPa causing O2 to split (dissociate) from hemoglobin & diffuse through tissue

8. Oxygen Transport cont
very little dissociation occurs until the partial prsr reaches 5.3 kPa, ensuring most O2 gets to tissues
still 70% of hemoglobin is still saturated when blood returns to heart!
therefore veins still have rich supply of O2

9. When Hemoglobin Releases O2

10. Carbon Dioxide Transport
20 times more soluble than O 9%
carried in the plasma
27%
combines with hemoglobin forming carbaminohemoglobin
64%
combines with water in plasma forming carbonic acid (H2CO3)
H2O + CO2  H+ + HCO3-
enzyme: carbonic anhydrase increases rate of rxn 250x
rapid conversion to H2CO3 decreases conc of CO2 in plasma, ensuring CO2 continues to diffuse in the blood

11. Controlling Acidity Level
Problem: Carbonic acid changes pH of blood=death (too acidic) must be buffered, job of hemoglobin
H2CO3 dissociates H2CO3  H+ + HCO3-
H+ ions combine with hemoglobin (bumping off O2), so it becomes a buffer while bicarbonate ions (HCO3-) are transported into plasma
O2 released can then move to the cells
at lungs O2 dislodges H+ ions from hemoglobin, to recombine with HCO3- :
H+ + HCO3-  H2O + CO2
CO2 diffuses from blood to alveoli eliminated when exhaled

12. Carbon Dioxide Transport

13. MAINTAINING CARBON DIOXIDE LEVELS Homeostasis
CO2 control = chemical receptor ensure CO2 does not accumulate in blood
during exercise cellular respiration increases
CO2 increases, activating chemical receptor in brain
send messages to muscles to increase breathing, which help flush excess CO2 from body

14. MAINTAINING OXYGEN LEVELS Homeostasis
O2 detector  a nerve in the walls of carotid artery detect low levels of O2
sends message to brain, which then sends message to muscles to increase breathing