1. Gas Exchange and Transport
Chapter 18a
Gas Exchange and Transport

2. Diffusion and solubility of gases Gas exchange in lungs and tissues
About this Chapter
Diffusion and solubility of gases
Gas exchange in lungs and tissues
Gas transport in the blood
Regulation of ventilation

3. Overview
Oxygen and carbon dioxide move into and out of the blood at pulmonary and systemic capillaries
Internal respiration
CO2 O2
Airways
Alveoli of lungs
CO2 O2 6
CO2 exchange at alveolar-capillary interface 1
Oxygen exchange at alveolar-capillary interface
CO2 O2
Pulmonary circulation 2
Oxygen transport 5
CO2 transport
Systemic circulation
CO2 O2 4
CO2 exchange at cells 3
Oxygen exchange at cells
CO2 O2
Cellular respiration
Cells
Nutrients
ATP
Figure 18-1

4. Diffusion and Solubility
Constants influencing diffusion in the lungs
Surface area
Contact between air and blood
Membrane thickness
Alveoli and endothelium
Diffusion distance
Distance between blood and air
Concentration gradient
Most important factor as others usually are constant

5. Pressure gradient Solubility Temperature Movement of Gases
Partial pressure change
Solubility
Gas into liquid
Temperature
Higher faster

6. Gases in Solution PO2 = 100 mm Hg PO2 = 100 mm Hg [O2] = 5.20 mmol/L
(b)
(c)
Figure 18-2a–c

7. Solubility difference between O2 and CO2
Gases in Solution P = O2 P =
CO2
100 mm Hg
100 mm Hg
[O2] = 5.20 mmol/L
[CO2] = 5.20 mmol/L P = O2 P =
CO2
100 mm Hg
100 mm Hg
[O2] = 0.15 mmol/L
[CO2] = 3.00 mmol/L
(c)
(d)
Solubility difference between O2 and CO2
Figure 18-2c–d

8. Gas Diffusion Figure 18-3 Alveoli Alveoli PO2 = 100 mm Hg
PCO2 = 40 mm Hg
PO2 = 40
PO2 = 100
PCO2 = 46
PCO2 = 40
Circulatory system
Circulatory system
PO2 = 40
PO2 = 100
PCO2 = 46
PCO2 = 40
PO2 < 40 mm Hg –
PCO2 > 46 mm Hg –
Peripheral tissue
Peripheral tissue
(a) Oxygen diffusion
(b) CO2 diffusion
Figure 18-3

9. Gas Exchange
PLAY
Interactive Physiology® Animation: Respiratory System: Gas Exchange

10. Partial Pressures
Table 18-1

11. Gas Exchange
Table 18-2

12. Causes of Low Alveolar PO2
Inspired air has abnormally low oxygen content
Altitude
Alveolar ventilation is inadequate
Decreased lung compliance
Increased airway resistance
Overdose of drugs
What types??

13. Alveolar Ventilation
Pathological conditions that reduce alveolar ventilation and gas exchange
Figure 18-4a

14. Alveolar Ventilation
Fewer alveoli
Figure 18-4b

15. Alveolar Ventilation
Low compliance
Figure 18-4c

16. Alveolar Ventilation
Figure 18-4d

17. Alveolar Ventilation
Figure 18-4e

18. Gas Exchange
Oxygen diffuses across alveolar epithelial cells and capillary endothelial cells to enter the plasma – respiratory membrane
Surfactant
Alveolar air space
Alveolar epithelium O2
Fused basement membranes
0.1–1.5 m
Nucleus of endothelial cell O2
Plasma
Capillary lumen
RBC
Figure 18-5

19. Pathological changes Gas Exchange
Decrease in amount of alveolar surface area
emphysema
Increase in thickness of alveolar membrane
fibrosis
Increase in diffusion distance between alveoli and blood
pneumonia

20. Used in cellular respiration
Oxygen Transport
Capillary endothelium
ARTERIAL BLOOD
O2 dissolved in plasma (~PO2) < 2% O2
O2 + Hb
Hb•O2 > 98%
Red blood cell
Alveolus
Alveolar membrane
Transport to cells
Cells
Hb•O2
Hb + O2 O2
Used in cellular respiration
O2 dissolved in plasma
Figure 18-6

21. Hemoglobin increases oxygen transport by blood
(a) Oxygen transport in blood without hemoglobin. Alveolar PO2 = arterial PO2
Hemoglobin increases oxygen transport by blood
PO2 = 100 mm Hg
Alveoli
O2 molecule
Arterial plasma
PO2 = 100 mm Hg
Oxygen dissolves in plasma.
O2 content of plasma = 3 mL O2/L blood O
O2 content of red blood cells = 0
Total O2 carrying capacity
3 mL O2/L blood
Figure 18-7a

22. Oxygen Transport Figure 18-7b
(b) Oxygen transport at normal PO2 in blood with hemoglobin
PO2 = 100 mm Hg
PO2 = 100 mm Hg
Red blood cells with hemoglobin are carry- ing 98% of their maximum load of oxygen.
O2 content of plasma = 003 mL O2/L blood
O2 content of red blood cells = 197 mL O2/L blood
Total O2 carrying capacity
200 mL O2/L blood
Figure 18-7b

23. Oxygen Transport Figure 18-7c
(c) Oxygen transport at reduced PO2 in blood with hemoglobin
PO2 = 28 mm Hg
PO2 = 28 mm Hg
Red blood cells carrying 50% of their maximum load of oxygen.
O2 content of plasma = mL O2/L blood
O2 content of red blood cells = mL O2/L blood
Total O2 carrying capacity
100.3 mL O2/L blood
Figure 18-7c

24. The Hemoglobin Molecule
 Chain
 Chain
Hemoglobin consists of 4 subunits, each centered around Fe2+
Heme group
(a)
Porphyrin ring
(b)
R = additional C, H, O groups
Figure 18-8

25. Oxygen-Hemoglobin Dissociation Curve
Figure 18-9

26. Oxygen Binding
Physical factors alter hemoglobin’s affinity for oxygen shift curve right or left pH
Temperature
pCO2
BPG
RBCs produce during hypoxia
Hb type
Fetal HbF
Figure 18-10a

27. Oxygen Binding
Figure 18-10b

28. Oxygen Binding
Figure 18-10c

29. 2,3-DPG decreases hemoglobin’s affinity for oxygen
Oxygen Binding
2,3-DPG decreases hemoglobin’s affinity for oxygen
Figure 18-11

30. Maternal and fetal hemoglobin have different oxygen-binding properties
Figure 18-12

31. Oxygen Binding
The total oxygen content of arterial blood depends on the amount of oxygen dissolved in plasma and bound to hemoglobin
TOTAL ARTERIAL O2 CONTENT
Oxygen dissolved in plasma (PO2 of plasma)
Oxygen bound to Hb
helps determine
is influenced by
Oxygen diffusion between alveoli and blood
Adequate perfusion of alveoli
Composition of inspired air
Alveolar ventilation
% Saturation of Hb
Total number of binding sites x
affected by
Rate and depth of breathing
Airway resistance
Lung compliance
Surface area
Diffusion distance
Hb content per RBC
Number of RBCs
PCO2 pH
Temperature
2,3–DPG x
Membrane thickness
Amount of interstitial fluid
Figure 18-13

32. Carbon Dioxide Transport
Dissolved: 7%
Converted to bicarbonate ion: 70%
Bound to hemoglobin: 23%
Hemoglobin also binds H+
Hb and CO2: carbaminohemoglobin
H20 + CO H2CO3 H+ + HCO3-

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

34. Summary of O2 and CO2 Exchange and Transport
Dry air = 760 mm Hg
PO2 = 160 mm Hg
PCO2 = 0.25 mm Hg
Alveoli
PO2 = 100 mm Hg
PCO2 = 40 mm Hg
CO2 O2
CO2 transport
HCO3– = 70% Hb•CO2 = 23% Dissolved CO2 = 7%
Arterial blood
PO2 = 100 mm Hg
Pulmonary circulation
PCO2 = 40 mm Hg
O2 transport Hb•O2 > 98% Dissolved O2 < 2% (~PO2)
Venous blood
PO2 = 40 mm Hg
PCO2 = 46 mm Hg
Systemic circulation
CO2 O2
Cells
PO2 < 40 mm Hg –
PCO2 > 46 mm Hg –
Figure 18-15

35. Gas Transport
PLAY
Interactive Physiology® Animation: Respiratory System: Gas Transport