1. Gas Exchange and Transport18

2. Overview Overview of oxygen and carbon dioxide exchange and transport
CO2 O2
Alveoli of lungs
Airways
Pulmonary
circulation
Cellular
respiration
ATP
Nutrients
Cells
Systemic
Oxygen exchange
at cells
Oxygen transport
CO2 exchange
at alveolar-capillary
interface
CO2 transport 1 2 3 4 5 6
Figure 18-1

3. Diffusion and Solubility
These are factors that affect diffusion if membrane permeability remains the same
Surface area- diffusion rate is proportional to available surface area
Constant- remains the same over a long period of time
Concentration gradient- diffusion rate is proportional to concentration gradient
Most important factor- O2 and CO2 gradients will be present at lung and tissue capillaries
Membrane thickness – diffusion rate is inversely proportional which is why walls are so thin
Constant- number of cells in walls should not change
Diffusion distance- diffusion rate is inversely proportional, another reason why walls are thin
Constant

4. Movement of Gases
These are factors that influence the movement of gasses from air into a liquid
Pressure gradient- drives gas flow
Solubility- the gas must be able to dissolve in the liquid, diffusion will continue until it reaches equilibrium, increased pressure may dissolve some gas if solubility is low.
Temperature- temperature is constant so it doesn’t play a role in the body unless there is pathology

5. Behavior of Gases in Solution
PO2 = 100 mm Hg
PO2 = 0 mm Hg
PO2 =
100 mm Hg
[O2] =
5.20 mmol/L
0.15 mmol/L
(a)
(b)
(c)
Initial state:
no O2 in solution
Oxygen dissolves.
At equilibrium, PO2 in air and water
is equal. Low O2 solubility means
concentrations are not equal.
The pressure equilibrium is not the same as the concentration dissolved.
Figure 18-2a–c

6. Behavior of Gases in Solution
Oxygen is less soluble in water than carbon dioxide
Figure 18-2c–d

7. Partial Pressures

8. Gas Exchange at the Alveoli and Cells
Gases move from areas of high partial presssures to areas of low partial pressure
Venous blood has the same Po2 as tissues
PLAY
Animation: Respiratory System: Gas Exchange
Figure 18-3

9. Gas Exchange
Oxygen diffuses across alveolar epithelial cells and capillary endothelial cells to enter the plasma
Gas exchange is rapid and blood flow is slow which allows for equilibrium in 1 second!
Figure 18-5

10. Gas Exchange
Hypoxia is not a disease, it is caused by something that decreases diffusion or oxygen deliver, that can cause disease

11. Oxygen Transport
98% of oxygen is bound to hemoglobin and the other 2% is dissolved in plasma O2
O2 dissolved in plasma (~ PO2) < 2%
O2 + Hb
ARTERIAL BLOOD
Alveolar
membrane
Alveolus
Capillary
endothelium
Red blood cell
Cells
Figure 18-6 (3 of 9)

12. Oxygen Transport
Because oxygen is not easily dissolve in water, hemoglobin is a protein that binds O2 and dramatically increased the amount of blood in the plasma O2
O2 dissolved in plasma (~ PO2) < 2%
O2 + Hb
Hb•O2
> 98%
ARTERIAL BLOOD
Alveolar
membrane
Alveolus
Capillary
endothelium
Red blood cell
Cells
Figure 18-6 (4 of 9)

13. Oxygen Transport
One reason why blood transfussions are used is to provide hemoglobin for efficient O2 transport. Researcher are working on carrier proteins O2
O2 dissolved in plasma (~ PO2) < 2%
O2 + Hb
Hb•O2
> 98%
ARTERIAL BLOOD
Alveolar
membrane
Alveolus
Capillary
endothelium
Transport
to cells
Red blood cell
Cells
Figure 18-6 (5 of 9)

14. Oxygen can travel bound to hemoglobin or to be dissolved in plasma
Oxygen Transport O2
O2 dissolved in plasma (~ PO2) < 2%
O2 dissolved in plasma
O2 + Hb
Hb•O2
> 98%
Hb + O2
ARTERIAL BLOOD
Alveolar
membrane
Alveolus
Capillary
endothelium
Transport
to cells
Red blood cell
Cells
Used in
cellular
respiration
Oxygen can travel bound to hemoglobin or to be dissolved in plasma
Figure 18-6 (9 of 9)

15. Oxygen Transport
The role of hemoglobin in oxygen transport
This shows that without hemoglobin very little oxygen would dissolve into the plasma- an amount that is not sufficient for cell demand
Figure 18-7a

16. Oxygen Transport
In the presence of hemoglobin a higher concentration can be dissolved in blood when pressure equilibrium is reached
Figure 18-7b

17. Oxygen Transport
If there are no problems with hemoblogin binding oxygen, then low blood oxygen levels could be due to a problem with ventilation
Figure 18-7c

18. The Hemoglobin Molecule
The amount of oxygen bound to hemoglobin depends on the PO2 of plasma- each hemoglobin can carry 4 oxygen molecules, the % saturation tells how much is carried.
Figure 18-8

19. Oxygen-Hemoglobin Dissociation Curve
In vitro testing reveals a varying amount of O2 saturation dependent on O2 partial pressure- it doesn’t reach 100% within physiological conditions
Figure 18-9

20. Oxygen Binding Physical factors alter hemoglobin’s affinity for oxygen
Changes can alter the hemoglobin conformation which influence delivery at tissues more than obtaining oxygen in the lungs.
Release more O2 at pH 7.2 (during exercise) than pH7.4
Figure 18-10a

21. Higher temperature decreases saturation shifting curve to the right
Oxygen Binding
Higher temperature decreases saturation shifting curve to the right
Figure 18-10b

22. Increased CO2 decreases O2 saturation
Oxygen Binding
Increased CO2 decreases O2 saturation
Figure 18-10c

23. Oxygen Binding
2,3-DPG alters hemoglobin’s affinity for oxygen
Released as a response to low O2 levels as can happen in anemia or high altitudes
Figure 18-11

24. Fetal hemoglobin has greater affinity
Oxygen Binding
Differences in oxygen-binding properties of maternal and fetal hemoglobin
Fetal hemoglobin has greater affinity
Figure 18-12

25. Oxygen Binding
Factors contributing to the total oxygen content of arterial blood
Figure 18-13

26. Carbon Dioxide Transport
Dissolved: 7% - although CO2 is more soluble in plasma than oxygen only a small amount is dissolved in it.
Converted to bicarbonate ion: 70% - an enzyme converts of the CO2 in RBCs into bicarbonate
Bound to hemoglobin: 23% -
Hemoglobin also binds H+ - hemoblogin acts as a buffer binding H+ to resists pH changes
Hb and CO2: carbaminohemoglobin – formed with CO2 and hemoglobin bind, it decreases affinity for O2

27. Carbon Dioxide Transport in the Blood
CO2
Dissolved CO2
(7%)
Cellular
respiration in
peripheral
tissues
VENOUS BLOOD
Alveoli
Red blood cell
Capillary
endothelium
Cell membrane
Figure 18-14

28. Carbon Dioxide Transport in the Blood
CO2
Dissolved CO2
(7%)
CO2 + Hb
Hb•CO2 (23%)
CO2 + H2O
HCO3–
H+ + Hb
Hb•H
Cellular
respiration in
peripheral
tissues
VENOUS BLOOD
Alveoli
Red blood cell
Capillary
endothelium
Cell membrane
H2CO3 CA
Figure 18-14

29. Carbon Dioxide Transport in the Blood
CO2
Dissolved CO2
(7%)
CO2 + Hb
Hb + CO2
Hb•CO2 (23%)
Hb•CO2
CO2 + H2O
HCO3–
HCO3– in
plasma (70%)
H+ + Hb
Hb•H
Cl–
Cellular
respiration in
peripheral
tissues
VENOUS BLOOD
Alveoli
Transport
to lungs
Red blood cell
Capillary
endothelium
Cell membrane
H2CO3 CA
Figure 18-14

30. Carbon Dioxide Transport in the Blood
CO2
Dissolved CO2
(7%)
CO2 + Hb
Hb + CO2
Hb•CO2 (23%)
Hb•CO2
CO2 + H2O
H2CO3
HCO3–
HCO3– in
plasma (70%) in
plasma
H+ + Hb
Hb•H
Cl–
Cellular
respiration
peripheral
tissues
VENOUS BLOOD
Alveoli
Transport
to lungs
Red blood cell
Capillary
endothelium
Cell membrane CA
Reverse chloride shift
H+ disassociate
H+ combine to form carbonic acid
Figure 18-14

31. Carbon Dioxide Transport in the Blood
CO2
Dissolved CO2
(7%)
CO2 + Hb
Hb + CO2
Hb•CO2 (23%)
Hb•CO2
CO2 + H2O
H2O + CO2
H2CO3
HCO3–
HCO3– in
plasma (70%) in
plasma
H+ + Hb
Hb•H
Cl–
Cellular
respiration
peripheral
tissues
VENOUS BLOOD
Alveoli
Transport
to lungs
Red blood cell
Capillary
endothelium
Cell membrane CA
Figure 18-14

32. Gas Transport: Summary
Gases move down their pressure gradients at the lungs and tissue capillaries
PLAY
Animation: Respiratory System: Gas Transport
Figure 18-15

33. Reflex Control of Ventilation
Figure 18-16

34. Regulation of Ventilation
Carotid body oxygen sensor releases neurotransmitter when PO2 decreases
Figure 18-18

35. Regulation of Ventilation
Central chemoreceptors monitor CO2 in cerebrospinal fluid
Figure 18-19

36. Regulation of Ventilation
Chemoreceptors in the brain and outside the CNS response to increased PCO2
Figure 18-20