1. Carbon Dioxide Transport
Carbon dioxide is transported in the blood in three forms
Dissolved in plasma – 7 to 10%
Chemically bound to hemoglobin – 20% is carried in RBCs as carbaminohemoglobin
Bicarbonate ion in plasma – 70% is transported as bicarbonate (HCO3–)

2. Transport and Exchange of Carbon Dioxide
Carbon dioxide diffuses into RBCs and combines with water to form carbonic acid (H2CO3), which quickly dissociates into hydrogen ions and bicarbonate ions
In RBCs, carbonic anhydrase reversibly catalyzes the conversion of carbon dioxide and water to carbonic acid
CO2 +
H2O 
H2CO3 H+
HCO3–
Carbon dioxide
Water
Carbonic acid
Hydrogen ion
Bicarbonate ion

3. Transport and Exchange of Carbon Dioxide
Figure 22.22a

4. Transport and Exchange of Carbon Dioxide
At the tissues:
Bicarbonate quickly diffuses from RBCs into the plasma
The chloride shift – to counterbalance the outrush of negative bicarbonate ions from the RBCs, chloride ions (Cl–) move from the plasma into the erythrocytes

5. Transport and Exchange of Carbon Dioxide
At the lungs, these processes are reversed
Bicarbonate ions move into the RBCs and bind with hydrogen ions to form carbonic acid
Carbonic acid is then split by carbonic anhydrase to release carbon dioxide and water
Carbon dioxide then diffuses from the blood into the alveoli

6. Transport and Exchange of Carbon Dioxide
Figure 22.22b

7. Haldane Effect
The amount of carbon dioxide transported is markedly affected by the PO2
Haldane effect – the lower the PO2 and hemoglobin saturation with oxygen, the more carbon dioxide can be carried in the blood

8. Haldane Effect
At the tissues, as more carbon dioxide enters the blood:
More oxygen dissociates from hemoglobin (Bohr effect)
More carbon dioxide combines with hemoglobin, and more bicarbonate ions are formed
This situation is reversed in pulmonary circulation

9. Haldane Effect
Figure 22.23

10. Influence of Carbon Dioxide on Blood pH
The carbonic acid–bicarbonate buffer system resists blood pH changes
If hydrogen ion concentrations in blood begin to rise, excess H+ is removed by combining with HCO3–
If hydrogen ion concentrations begin to drop, carbonic acid dissociates, releasing H+

11. Carbon Dioxide Transport
Dissolved: 7%
Converted to bicarbonate ion in rbc: 70%
Bound to hemoglobin: 23%
Hemoglobin also binds H+,
Hb and CO2: carbaminohemoglobin

12. 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

13. Carbon Dioxide Transport in the Blood
CO2
Cellular
respiration in
peripheral
tissues
VENOUS BLOOD
Alveoli
Capillary
endothelium
Cell membrane
Figure (1 of 17)

14. Carbon Dioxide Transport in the Blood
CO2
Dissolved CO2
(7%)
Cellular
respiration in
peripheral
tissues
VENOUS BLOOD
Alveoli
Capillary
endothelium
Cell membrane
Figure (2 of 17)

15. 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 (3 of 17)

16. Carbon Dioxide Transport in the Blood
CO2
Dissolved CO2
(7%)
CO2 + Hb
Hb•CO2 (23%)
Cellular
respiration in
peripheral
tissues
VENOUS BLOOD
Alveoli
Red blood cell
Capillary
endothelium
Cell membrane
Figure (4 of 17)

17. Carbon Dioxide Transport in the Blood
CO2
Dissolved CO2
(7%)
CO2 + Hb
Hb•CO2 (23%)
CO2 + H2O
Cellular
respiration in
peripheral
tissues
VENOUS BLOOD
Alveoli
Red blood cell
Capillary
endothelium
Cell membrane
H2CO3 CA
Figure (5 of 17)

18. Carbon Dioxide Transport in the Blood
CO2
Dissolved CO2
(7%)
CO2 + Hb
Hb•CO2 (23%)
CO2 + H2O
HCO3–
H+ + Hb
Cellular
respiration in
peripheral
tissues
VENOUS BLOOD
Alveoli
Red blood cell
Capillary
endothelium
Cell membrane
H2CO3 CA
Figure (6 of 17)

19. 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 (7 of 17)

20. Carbon Dioxide Transport in the Blood
CO2
Dissolved CO2
(7%)
CO2 + Hb
Hb•CO2 (23%)
CO2 + H2O
HCO3–
HCO3– in
plasma (70%)
H+ + Hb
Hb•H
Cl–
Cellular
respiration in
peripheral
tissues
VENOUS BLOOD
Alveoli
Red blood cell
Capillary
endothelium
Cell membrane
H2CO3 CA
Figure (8 of 17)

21. Carbon Dioxide Transport in the Blood
CO2
Dissolved CO2
(7%)
CO2 + Hb
Hb•CO2 (23%)
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 (9 of 17)

22. Carbon Dioxide Transport in the Blood
CO2
Dissolved CO2
(7%)
CO2 + Hb
Hb•CO2 (23%)
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 (10 of 17)

23. 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 (11 of 17)

24. 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 (12 of 17)

25. 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%) in
plasma
H+ + Hb
Hb•H
Cl–
Cellular
respiration
peripheral
tissues
VENOUS BLOOD
Alveoli
Transport
to lungs
Red blood cell
Capillary
endothelium
Cell membrane
H2CO3 CA
Figure (13 of 17)

26. 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%) in
plasma
H+ + Hb
Hb•H
Cl–
Cellular
respiration
peripheral
tissues
VENOUS BLOOD
Alveoli
Transport
to lungs
Red blood cell
Capillary
endothelium
Cell membrane
H2CO3 CA
Figure (14 of 17)

27. 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
Figure (15 of 17)

28. 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 (16 of 17)

29. 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 (17 of 17)

30. Gas Transport: Summary
Figure 18-15

31. Influence of Carbon Dioxide on Blood pH
Changes in respiratory rate can also:
Alter blood pH
Provide a fast-acting system to adjust pH when it is disturbed by metabolic factors

32. Deep-diving air-breathers stockpile oxygen and deplete it slowly
When an air-breathing animal swims underwater, it lacks access to the normal respiratory medium.
Most humans can only hold their breath for 2 to 3 minutes and swim to depths of 20 m or so.
However, a variety of seals, sea turtles, and whales can stay submerged for much longer times and reach much greater depths.
Fig
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

33. One adaptation of these deep-divers, such as the Weddell seal, is an ability to store large amounts of O2 in the tissues.
Compared to a human, a seal can store about twice as much O2 per kilogram of body weight, mostly in the blood and muscles.
About 36% of our total O2 is in our lungs and 51% in our blood.
In contrast, the Weddell seal holds only about 5% of its O2 in its small lungs and stockpiles 70% in the blood.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

34. Several adaptations create these physiological differences between the seal and other deep-divers in comparison to humans.
First, the seal has about twice the volume of blood per kilogram of body weight as a human.
Second, the seal can store a large quantity of oxygenated blood in its huge spleen, releasing this blood after the dive begins.
Third, diving mammals have a high concentration of an oxygen-storing protein called myoglobin in their muscles.
This enables a Weddell seal to store about 25% of its O2 in muscle, compared to only 13% in humans.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

35. Diving vertebrates not only start a dive with a relatively large O2 stockpile, but they also have adaptations that conserve O2.
They swim with little muscular effort and often use buoyancy changes to glide passively upward or downward.
Their heart rate and O2 consumption rate decreases during the dive and most blood is routed to the brain, spinal cord, eyes, adrenal glands, and placenta (in pregnant seals).
Blood supply is restricted or even shut off to the muscles, and the muscles can continue to derive ATP from fermentation after their internal O2 stores are depleted.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings