Transcript video slide

• Concept 42.7: Respiratory pigments bind and
transport gases
• The metabolic demands of many organisms
require that the blood transport large quantities
of O2 and CO2
• Gases diffuse down pressure gradients in the
lungs and other organs
• Diffusion of a gas depends on differences in a
quantity called partial pressure
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• A gas always diffuses from a region of higher
partial pressure to a region of lower partial
pressure
• In the lungs and in the tissues, O2 and CO2
diffuse from where their partial pressures are
higher to where they are lower
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Inhaled air
Exhaled air
160 0.2
O2 CO2
120 27
Alveolar spaces
O2 CO2
104
Alveolar
epithelial
cells
40
O2 CO2
Blood
entering
alveolar
capillaries
40
O2
CO2
2
1
O2
Alveolar
capillaries
of lung
45
O2 CO2
104
Pulmonary
veins
Systemic
arteries
Systemic
veins
CO2
40
40
O2 CO2
Pulmonary
arteries
Blood
leaving
tissue
capillaries
Blood
leaving
alveolar
capillaries
Heart
Tissue
capillaries
O2
3
4
45
O2
CO2
Tissue
cells
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100
40
O2 CO2
O2 CO2
Figure 42.27
Blood
entering
tissue
capillaries
<40 >45
O2 CO2
Respiratory Pigments
• Respiratory pigments are proteins that
transport oxygen
– Greatly increase the amount of oxygen that
blood can carry
• The respiratory pigment of almost all
vertebrates is the protein hemoglobin,
contained in the erythrocytes
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• Hemoglobin must reversibly bind O2, loading
O2 in the lungs and unloading it in other parts
of the body
Heme group
Iron atom
O2 loaded
in lungs
O2 unloaded
In tissues
Polypeptide chain
Figure 42.28
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O2
O2
• Loading and unloading of O2 depend on
cooperation between the subunits of the
hemoglobin molecule
• The binding of O2 to one subunit induces the
other subunits to bind O2 with more affinity
• Cooperative O2 binding and release is evident
in the dissociation curve for hemoglobin
• A drop in pH lowers the affinity of hemoglobin
for O2
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O2 saturation of hemoglobin (%)
(a) PO2 and Hemoglobin Dissociation at 37°C and pH 7.4
O2 unloaded from
hemoglobin
during normal
metabolism
100
80
O2 reserve that can
be unloaded from
hemoglobin to
tissues with high
metabolism
60
40
20
0
0
20
40
60
Tissues during Tissues
at rest
exercise
80 100
Lungs
(b) pH and Hemoglobin Dissociation
Figure 42.29a, b
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O2 saturation of hemoglobin (%)
PO2 (mm Hg)
100
pH 7.4
80
60
pH 7.2
40
20
0
0
20
40
Bohr shift:
Additional O2
released from
hemoglobin at
lower pH
(higher CO2
concentration)
60
PO2 (mm Hg)
80 100
Carbon Dioxide Transport
• Hemoglobin also helps transport CO2 and
assists in buffering
• Carbon from respiring cells diffuses into the
blood plasma and then into erythrocytes and is
ultimately released in the lungs
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1
2
Carbon dioxide produced by
body tissues diffuses into the
interstitial fluid and the plasma.
Over 90% of the CO2 diffuses
into red blood cells, leaving only 7%
in the plasma as dissolved CO2.
Tissue cell
Some CO2 is picked up and
transported by hemoglobin.
1
Blood plasma CO
2
within capillary
Capillary
wall
2
CO2
Carbonic acid dissociates into a
biocarbonate ion (HCO3–) and a
hydrogen ion (H+).
HCO3–
7
Hemoglobin binds most of the
H+ from H2CO3 preventing the H+
from acidifying the blood and thus
preventing the Bohr shift.
Figure 42.30
9
Carbonic acid is converted back
into CO2 and water.
10
CO2 formed from H2CO3 is unloaded
from hemoglobin and diffuses into the
interstitial fluid.
To lungs
CO2 transport
to lungs
HCO3–
8
H2CO3
Hb
9
11 CO2
Hemoglobin
releases
CO2 and H+
H2O
CO2
6
In the HCO3– diffuse
from the plasma red blood cells,
combining with H+ released from
hemoglobin and forming H2CO3.
6
HCO3– + H+
5
8
Red
Hemoglobin
H2CO3
blood Carbonic acid Hb
picks up
cell
CO2 and H+
5
+ H+
Bicarbonate
However, most CO2 reacts with water
in red blood cells, forming carbonic
acid (H2CO3), a reaction catalyzed by
carbonic anhydrase contained. Within
red blood cells.
Most of the HCO3– diffuse
into the plasma where it is
carried in the bloodstream to
the lungs.
3
4
HCO3–
4
7
Interstitial CO
2
fluid
H2O
3
CO2 transport
from tissues
CO2 produced
CO2
CO2 10
CO2 11
Alveolar space in lung
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diffuses into the alveolar
space, from which it is expelled
during exhalation. The reduction
of CO2 concentration in the plasma
drives the breakdown of H2CO3
Into CO2 and water in the red blood
cells (see step 9), a reversal of the
reaction that occurs in the tissues
(see step 4).