1. Respiration: Part 3 How does gas exchange happen?
Substances diffuse from high concentrations to low concentrations
Example: Scent molecules move across a room

2. Gas exchange: Diffusion of gases
Gases move by diffusion from high to low concentration
capillaries are thin-walled tubes of circulatory system
alveoli are thin-walled sacs of respiratory system
capillaries in lungs
capillaries in muscle O2 O2 O2 O2
CO2
CO2
CO2
CO2
blood
lungs
blood
body

3. External Respiration (Lungs)
Exchange between gases in the air and the blood
Through Alveoli and capillary walls (only one cell thick!)

4. How do you diffuse the most O2 into the blood?
Alveolus
Lung Capillary O2 O2
Hemoglobin O2 O2 O2 O2 O2 O2 O2 O2 O2 O2 O2 = O2 O2 O2 O2 O2 O2 O2
HIGH Concentration
LOW Concentration

5. Result: We get MORE oxygen diffusing into the blood!
What just happened?
Breathe in and there is more O2 in the alveoli than in the blood
O2 moves from HIGH to LOW concentration
Alveoli and blood are at the same concentration
Hemoglobin took up four more O2
Alveoli had more O2 than the blood again
Result: We get MORE oxygen diffusing into the blood!

6. Helpful Hemoglobin! (Hb)
Contains iron
250 million Hb / red blood cell
4 O2 molecules can attach to each Hb molecule
Increases carrying capacity of O2 by 60 times O2 O2 O2 O2

7. Internal Respiration (Body)
Exchange between gases in the blood and the tissues
Through capillary walls into cells

8. How does the O2 get from the blood to the cells?
Body Cell
Body Capillary
Hemoglobin O2 O2 O2 O2 O2 O2 O2 O2 = O2 O2 O2 O2 O2 O2 O2
LOW Concentration
HIGH Concentration

9. What happened this time?
Blood arrives with a HIGH concentration of O2
Cells have a LOW concentration of O2
O2 diffuses out of the blood into the cells (HIGH  LOW)
Hb gives up its four O2
There is more O2 in the blood again
More O2 diffuses out of the blood into the cells
Result: We get MORE oxygen diffusing into the cells!

10. Consider this reaction:
Hb + O  HbO2
(hemoglobin + O2) (oxyhemoglobin)
Why will this help you to diffuse more oxygen into the blood?
When there is lots of O2 the reaction shifts this way:
Hb + O2  HbO2
When there is lots of HbO2 the reaction shifts this way:
Hb + O2  HbO2
Happens in LUNGS
Happens in TISSUES

11. How do we maximize the transfer of O2 using Hb?
Effect of temperature:
Hb gives up O2 better at higher temperatures
Hb attaches to O2 better at lower temperatures
Effect of pH:
At higher or neutral pH, Hb attaches to O2 better
At lower pH, Hb gives up O2 better

13. What are the best conditions?
For TAKING UP O2?
pH =
Temperature =
This occurs in the _________________.
For GIVING AWAY O2?
High pH (Basic)
Low Temperature (Cool)
Lungs
Low pH (Acid)
High Temperature (Hot)
Tissues

14. What happens with CO2?
CO2 also diffuses from HIGH to LOW concentration
In the lungs:
Blood is HIGH in CO2  Alveolus is LOW in CO2
In the tissues:
Cells are HIGH in CO2  Blood is LOW in CO2
Some CO2 changes into carbonic acid (H2CO3) in the blood
This lets more CO2 diffuse in from the cells

15. CO2 produced
INTERSTITIAL FLUID
CO2
BLOOD PLASMA WITHIN CAPILLARY
Capillary wall
H2O
H2CO3
RED BLOOD CELL
HCO3– + H+
Hemoglobin picks up CO2 and H+
ALVEOLAR SPACE IN LUNG
Hemoglobin releases CO2 and H+

16. Why is carbon monoxide poisonous?
CO + Hb   HbCO
Carbon monoxide + hemoglobin carboxyhemoglobin
Hb has an affinity for carbon monoxide 230 times greater than its affinity for O2
 Hemoglobin can’t carry oxygen because it is taken up with carbon monoxide