Gas Transport and Exchange

Question 1

Alveolar Exchange

Answer 1

Conditions needed to allow alveolar gas exchange:
• wet surface - O2 dissolved before diffusing
• thin epithelia - smaller diffusion distance
• little ECF - smaller diffusion distance

Question 2

Factors Affecting Solubility of Gases

Answer 2

• Temperature: gases are more soluble in liquid at colder temperatures
• Pressure: solubility is directly proportional to pressure (lower at higher altitudes)
• Solubility is different for different gases (O2 is not very soluble but CO2 is)

Question 3

O2 Exchange at Tissues

Answer 3

• O2 diffusion from blood into tissue cells
• pressure of O2 is higher in blood
• pressure of O2 is lower in tissues

Question 4

O2 Transport

Answer 4

• O2 is not very soluble in the blood (only 2% dissolves)
• the reaction with Hb is reversible
• In the lungs:
Hemoglobin + Oxygen -> Oxyhemoglobin
• In the tissues:
Oxyhemoglobin -> Hemoglobin + Oxygen

Question 5

CO2 Exchange in the Lungs

Answer 5

• CO2 diffuses from the blood through the alveolar thin cells and into the lungs
• pressure of CO2 is higher in the blood
• pressure of O2 is lower in alveoli

Question 6

CO2 Transport

Answer 6

1. Dissolved CO2 in blood
2. Bicarbonate Ions
3. Bound to Hb

Question 7

CO2 Bound to Hb

Answer 7

• CO2 does not bind to iron like O2
• CO2 binds to the amino groups of Hb
• 10% of CO2 bound to and transported by Hb
• HbCO2 = carbaminohaemoglohin

Question 8

Bohr Effect

Answer 8

• in areas of high CO2, Hb releases O2 more easily
• CO2 causes blood pH to decrease (more H+)
• H+ ions attach your Hb, causing a shape change
• O2 doesn’t fit into Hb “pockets” as well, gets released
• opposite effect (at lungs) is called Haldane Effect

Question 9

Solubility of Gases

Answer 9

• gases must dissolve before crossing the respiratory surface
• CO2 and O2 also dissolve into blood to be transported
- Solubility = dissolving of gases into liquids

Question 10

O2 Exchange in the Lungs

Answer 10

• O2 diffusion through alveolar thin cells into blood

• pressure of O2 is higher in alveoli
• pressure of O2 is lower in blood

Question 11

O2 Transport: Hemoglobin (Hb)

Answer 11

• 1 Hb contains 4 heme groups 
• each heme group can bind with one O2 molecule
- O2 bind to the iron atom
- each Hb can carry 4 O2 molecules 
• 98% of O2 is moved via Hb
• 2% of O2 is moved via plasma

Question 12

Reaction Between O2 and Hb

Answer 12

• O2 combines with Hb in oxygen-rich situations
- i.e. the lungs
• HbO2 dissociates in oxygen rich situations
- i.e. the tissues

Question 13

CO2 Exchange at Tissues

Answer 13

• CO2 diffusion from tissue cells into blood

• pressure of CO2 is higher in tissues
• pressure of CO2 is lower in blood

Question 13

CO2 Exchange at Tissues

Answer 13

• CO2 diffusion from tissue cells into blood

• pressure of CO2 is higher in tissues
• pressure of CO2 is lower in blood

Question 14

CO2 Transport: Dissolved CO2

Answer 14

• CO2 is more soluble in blood

* 5% of CO2 is dissolved into plasma unchanged

Question 15

CO2 Transport: Bicarbonate Ions (HCO3)

Answer 15

• CO2 combines with water to form carbonic acid

* 85% of CO2 transported via HCO3