Chapter 22 Respiratory System Lecture 8 Part 2: O 2 and CO 2 Transport Marieb’s Human Anatomy and Physiology Ninth Edition Marieb Hoehn
Dec 21, 2015
Chapter 22Respiratory System
Lecture 8
Part 2: O2 and CO2 Transport
Marieb’s Human
Anatomy and Physiology
Ninth Edition
Marieb Hoehn
4
Diffusion Through Respiratory MembraneThe 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)
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)
Figure from: Hole’s Human A&P, 12th
edition, 2010
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
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
But what special properties of the Hb molecule allow it to reversibly bind O2?
Lungs
Tissues
Figure from: Hole’s Human A&P, 12th
edition, 2010
PO2 ≈ 40 mm Hg PO2 ≈ 100 mm Hg
10
The O2-Hb Dissociation Curve
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
Figure from: Hole’s Human A&P, 12th
edition, 2010
11
Oxygen ReleaseAmount 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-
CO2 exchange in TISSUES
Figure from: Hole’s Human A&P, 12th
edition, 2010
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-
CO2 exchange in TISSUES
Figure from: Hole’s Human A&P, 12th
edition, 2010
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
CO2 exchange in LUNGS
Figure from: Hole’s Human A&P, 12th
edition, 2010
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