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

• 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

–)

Carbon Dioxide Transport

• 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

Transport and Exchange of Carbon Dioxide

CO2+H2OH2CO3H++HCO3–

Carbon dioxide

WaterCarbonic

acidHydrogen

ionBicarbonate

ion


Figure 22.22a

• 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


• 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



Figure 22.22b

• 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

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

Haldane Effect

Haldane Effect

Figure 22.23

• 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+

Influence of Carbon Dioxide on Blood pH

Carbon Dioxide Transport•Dissolved: 7%

•Converted to bicarbonate ion in rbc: 70%•Bound to hemoglobin: 23%

–Hemoglobin also binds H ,+

–Hb and CO2: carbaminohemoglobin

Figure 18-14

Carbon Dioxide Transport in the Blood

CO2

CO2

Dissolved CO2

(7%)

Dissolved CO2 Dissolved CO2

CO2 + Hb

Hb + CO2

Hb•CO2 (23%)

Hb•CO2

CO2 + H2O

H2O + CO2H2CO3

HCO3–

HCO3–

HCO3– in

plasma (70%)

HCO3–

inplasma

H+ + Hb Hb•H

H+ + HbHb•H

Cl–

Cl–

Cellularrespiration

inperipheral

tissues

VENOUS BLOOD

Alveoli

Transportto lungs

Red blood cell

Capillaryendothelium

Cell membrane

CA

H2CO3

CA

Figure 18-14 (1 of 17)


CO2

Cellularrespiration

inperipheral

tissues

VENOUS BLOOD

Alveoli


Cell membrane

Figure 18-14 (2 of 17)

Carbon Dioxide Transport in the BloodCO2 Dissolved CO2

(7%)Cellular

respirationin

peripheraltissues

VENOUS BLOOD

Alveoli


Cell membrane

Figure 18-14 (3 of 17)


CO2 Dissolved CO2

(7%)

CO2

Cellularrespiration

inperipheral

tissues

VENOUS BLOOD

Alveoli

Red blood cell


Cell membrane

Figure 18-14 (4 of 17)


CO2 Dissolved CO2

(7%)

CO2 + Hb Hb•CO2 (23%)

Cellularrespiration

inperipheral

tissues

VENOUS BLOOD

Alveoli

Red blood cell


Cell membrane

Figure 18-14 (5 of 17)


CO2 Dissolved CO2

(7%)

CO2 + Hb Hb•CO2 (23%)

CO2 + H2O

Cellularrespiration

inperipheral

tissues

VENOUS BLOOD

Alveoli

Red blood cell


Cell membrane

H2CO3

CA

Figure 18-14 (6 of 17)


(7%)

CO2 + Hb Hb•CO2 (23%)

CO2 + H2OHCO3

–

H+ + Hb

Cellularrespiration

inperipheral

tissues

VENOUS BLOOD

Alveoli

Red blood cell


Cell membrane

H2CO3

CA

Figure 18-14 (7 of 17)


CO2 Dissolved CO2

(7%)

CO2 + Hb Hb•CO2 (23%)

CO2 + H2OHCO3

–

H+ + Hb Hb•H

Cellularrespiration

inperipheral

tissues

VENOUS BLOOD

Alveoli

Red blood cell


Cell membrane

H2CO3

CA

Figure 18-14 (8 of 17)


CO2 Dissolved CO2

(7%)

CO2 + Hb Hb•CO2 (23%)

CO2 + H2OHCO3

– HCO3– in

plasma (70%)H+ + Hb Hb•H

Cl–

Cellularrespiration

inperipheral

tissues

VENOUS BLOOD

Alveoli

Red blood cell


Cell membrane

H2CO3

CA

Figure 18-14 (9 of 17)


(7%)

CO2 + Hb Hb•CO2 (23%)

CO2 + H2OHCO3

– HCO3– in


Cl–

Cellularrespiration

inperipheral

tissues

VENOUS BLOOD

Alveoli

Transportto lungs

Red blood cell


Cell membrane

H2CO3

CA

Figure 18-14 (10 of 17)


CO2

CO2

Dissolved CO2

(7%)


CO2 + Hb Hb•CO2 (23%)

CO2 + H2OHCO3

– HCO3– in


Cl–

Cellularrespiration

inperipheral

tissues

VENOUS BLOOD

Alveoli

Transportto lungs

Red blood cell


Cell membrane

H2CO3

CA

Figure 18-14 (11 of 17)


CO2

CO2

Dissolved CO2

(7%)


CO2 + Hb

Hb + CO2

Hb•CO2 (23%)

Hb•CO2

CO2 + H2OHCO3

– HCO3– in


Cl–

Cellularrespiration

inperipheral

tissues

VENOUS BLOOD

Alveoli

Transportto lungs

Red blood cell


Cell membrane

H2CO3

CA

Figure 18-14 (12 of 17)

Carbon Dioxide Transport in the BloodCO2

CO2

Dissolved CO2

(7%)


CO2 + Hb

Hb + CO2

Hb•CO2 (23%)

Hb•CO2

CO2 + H2OHCO3

– HCO3– in


Cl–

Cellularrespiration

inperipheral

tissues

VENOUS BLOOD

Alveoli

Transportto lungs

Red blood cell


Cell membrane

H2CO3

CA

Figure 18-14 (13 of 17)


CO2

CO2

Dissolved CO2

(7%)


CO2 + Hb

Hb + CO2

Hb•CO2 (23%)

Hb•CO2

CO2 + H2OHCO3

–

HCO3–

HCO3– in

plasma (70%)

HCO3–

inplasma

H+ + Hb Hb•H

Cl–

Cl–

Cellularrespiration

inperipheral

tissues

VENOUS BLOOD

Alveoli

Transportto lungs

Red blood cell


Cell membrane

H2CO3

CA

Figure 18-14 (14 of 17)


CO2

CO2

Dissolved CO2

(7%)


CO2 + Hb

Hb + CO2

Hb•CO2 (23%)

Hb•CO2

CO2 + H2OHCO3

–

HCO3–

HCO3– in

plasma (70%)

HCO3–

inplasma

H+ + Hb Hb•H

H+ + HbHb•H

Cl–

Cl–

Cellularrespiration

inperipheral

tissues

VENOUS BLOOD

Alveoli

Transportto lungs

Red blood cell


Cell membrane

H2CO3

CA

Figure 18-14 (15 of 17)


CO2

CO2

Dissolved CO2

(7%)


CO2 + Hb

Hb + CO2

Hb•CO2 (23%)

Hb•CO2

CO2 + H2O

H2CO3

HCO3–

HCO3–

HCO3– in

plasma (70%)

HCO3–

inplasma

H+ + Hb Hb•H

H+ + HbHb•H

Cl–

Cl–

Cellularrespiration

inperipheral

tissues

VENOUS BLOOD

Alveoli

Transportto lungs

Red blood cell


Cell membrane

H2CO3

CA

Figure 18-14 (16 of 17)

Carbon Dioxide Transport in the BloodCO2

CO2

Dissolved CO2

(7%)


CO2 + Hb

Hb + CO2

Hb•CO2 (23%)

Hb•CO2

CO2 + H2O

H2O + CO2H2CO3

HCO3–

HCO3–

HCO3– in

plasma (70%)

HCO3–

inplasma

H+ + Hb Hb•H

H+ + HbHb•H

Cl–

Cl–

Cellularrespiration

inperipheral

tissues

VENOUS BLOOD

Alveoli

Transportto lungs

Red blood cell


Cell membrane

H2CO3

CA

CA

Figure 18-14 (17 of 17)


CO2

CO2

Dissolved CO2

(7%)


CO2 + Hb

Hb + CO2

Hb•CO2 (23%)

Hb•CO2

CO2 + H2O

H2O + CO2H2CO3

HCO3–

HCO3–

HCO3– in

plasma (70%)

HCO3–

inplasma

H+ + Hb Hb•H

H+ + HbHb•H

Cl–

Cl–

Cellularrespiration

inperipheral

tissues

VENOUS BLOOD

Alveoli

Transportto lungs

Red blood cell


Cell membrane

H2CO3

CA

CA

Figure 18-15

Gas Transport: Summary

•Changes in respiratory rate can also:–Alter blood pH

–Provide a fast-acting system to adjust pH when it is disturbed by metabolic factors

Influence of Carbon Dioxide on Blood pH

• 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.

Deep-diving air-breathers stockpile oxygen and deplete it slowly

Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Fig. 42.30

• 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.


• 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.


• 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.


Documents

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