1. Chapter 22 Respiratory System Lecture 8 Part 2: O2 and CO2 Transport
Marieb’s Human
Anatomy and Physiology
Ninth Edition
Marieb w Hoehn
Chapter 22
Respiratory System
Lecture 8
Part 2: O2 and CO2 Transport
Slides 1-15; 80 min (with review of syllabus and Web sites) [Lecture 1]
Slides 16 – 38; 50 min [Lecture 2]
118 min (38 slides plus review of course Web sites and syllabus)

2. Just a Quick Review!
Atmosphere is composed of several gases, each exerting its own partial pressure, PO2
P  1/V (Boyle’s Law)
Inspiration
Normal
Forced or maximal
Expiration
The respiratory membrane for gas exchange

3. Diffusion Across Respiratory Membrane
Figure from: Hole’s Human A&P, 12th edition, 2010

4. Diffusion Through Respiratory Membrane
The driving force for the exchange of gases between alveolar air and capillary blood is the difference in partial pressure between the gases. (PP gradients of different gases are independent)
Figure from: Hole’s Human A&P, 12th edition, 2010
At a given temperature, the amount of a particular gas in solution is directly proportional to its partial pressure outside the solution (Henry’s Law)

5. Efficiency of Respiratory Membrane Diffusion
Diffusion of gases across the RM of the lung is efficient due to
Large partial pressure differences
Small distances
Lipid solubility of gases
Large total surface area
Blood flow and air flow are coordinated

6. Composition of Inspired and Alveolar Air
From: Saladin, Anatomy & Physiology, McGraw Hill, 2007

7. Factors Affecting O2 and CO2 Transport
O2 and CO2 have limited solubility in plasma; so a more efficient way to carry these gases is needed...
This problem is solved by RBCs
Bind O2 to hemoglobin
Use CO2 to make soluble compounds
Reactions in RBCs are
Temporary
Completely reversible
Less than 2% of O2 is dissolved in plasma; about 5-7% of CO2 is dissolved in plasma

8. Oxygen Transport
Most oxygen binds to hemoglobin to form oxyhemoglobin (HbO2)
Oxyhemoglobin releases oxygen in the regions of body cells
Much oxygen is still bound to hemoglobin in the venous blood
Figure from: Hole’s Human A&P, 12th edition, 2010
PO2 ≈ 100 mm Hg
PO2 ≈ 40 mm Hg
*PO2 in blood leaving lungs is about 95 mm Hg (not 100) because some of the blood leaving the alveolar capillaries mixes with venous blood returning to the heart from blood vessels serving other structures in the lung (which is not oxygenated) and this reduces the PO2 from 100 mm Hg at the alveoli to about 95 mm Hg in the arterial blood.
Tissues
Lungs
But what special properties of the Hb molecule allow it to reversibly bind O2?

9. Review of Hemoglobin’s Structure
Figure From: Martini, Anatomy & Physiology, Prentice Hall, 2001

10. The O2-Hb Dissociation Curve
Figure from: Hole’s Human A&P, 12th edition, 2010
Recall that Hb can bind up to 4 molecules of O2 = 100% saturation
At 75% saturation, Hb binds 3 molecules of O2 on average
Sigmoidal (S) shape of curve indicates that the binding of one O2 makes it easier to bind the next O2
This curve tells us what the percent saturation of Hb will be at various partial pressures of O2

11. Oxygen Release
Amount of oxygen released from oxyhemoglobin increases as
partial pressure of carbon dioxide increases
the blood pH decreases and [H+] increases (Bohr Effect; shown below)
blood temperature increases (not shown)
concentration of 2,3 bisphosphoglycerate (BPG) increases (not shown)
Figure from: Hole’s Human A&P, 12th edition, 2010

12. Carbon Dioxide Transport in Tissues
dissolved in plasma (7%)
combined with hemoglobin as carbaminohemoglobin(15-25%)
in the form of bicarbonate ions (68-78%)
CO2 + H2O ↔ H2CO3
H2CO3 ↔ H+ + HCO3-
Figure from: Hole’s Human A&P, 12th edition, 2010
CO2 exchange in TISSUES

14. Carbon Dioxide Transport in Tissues
dissolved in plasma (7%)
combined with hemoglobin as carbaminohemoglobin(15-25%)
in the form of bicarbonate ions (68-78%)
CO2 + H2O ↔ H2CO3
H2CO3 ↔ H+ + HCO3-
Figure from: Hole’s Human A&P, 12th edition, 2010
CO2 exchange in TISSUES

15. Chloride Shift bicarbonate ions diffuse out RBCs
chloride ions from plasma diffuse into RBCs
electrical balance is maintained
Figure from: Hole’s Human A&P, 12th edition, 2010

16. Carbon Dioxide Transport in Lungs
Figure from: Hole’s Human A&P, 12th edition, 2010
CO2 exchange in LUNGS

17. Review Oxygen travels in the blood bound to Hb
Four O2 molecules can be bound to 1 Hb
O2 bound to Hb - oxyhemoglobin
Uptake and release of O2 is dependent upon PO2 in alveoli and tissues
Several factors can increase the release of O2 from Hb
Increased PCO2
Increased [H+] (decreased pH)
Increased temperature of blood

18. Review Carbon dioxide can travel in several ways
Dissolved in plasma (7%)
As carbaminohemoglobin (15-25%)
As HCO3- ion (70%)
Recall: H2O + CO2 ↔ H2CO3 ↔ H+ + HCO3-
Carbonic anhydrase in RBCs accelerates interconversion between CO2 and HCO3-
H+ combines with or dissociates from Hb
HCO3- diffuses into plasma or into RBCs
Cl- diffuses into RBC (chloride shift) as HCO3- exits
Diffusion of CO2 is related to PCO2 in alveoli and tissues