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Section III Oxygen and Carbon
Dioxide Transport in Blood
1
Basic Mechanism of the Gases Transportation
Two forms of the gases: physical dissolution and
chemical combination.
Most of oxygen and carbon dioxide in the blood is
transported in chemical combination
Only the gas in physical dissolution express PP and
diffuse to a place with low PP.
Dynamic balance between the two forms:
Physical dissolution
PP
PP
Chemical combination
2
I. Transport of Oxygen
3
Oxygen Transport
• Method
Percentage
• Dissolved in Plasma
1.5 %
• Combined with Hemoglobin
98.5 %
Bound to Hgb
Dissolved
4
Hemoglobin Structure
Protein made up of 4 subunits
Every subunit contains a heme moiety attached to a
polypeptide chain.
5
Oxyhemoglobin Formation
• An oxygen molecule reversibly attaches to the
heme portion of hemoglobin.
• The heme unit contains iron ( +2 ) which
provides the attractive force.
O2 + Hb
HbO2
6
In normal adults, most of the hemoglobin
contains 2α and 2 β chains.
Each of the 4 iron atoms can bind reversibly on
O2 molecule.
The iron stays in the ferrous state, so that the
reaction is an oxygenation, not an oxidation.
7
When saturated with O2 (4 O2 in one
hemoglobin molecule), it is always written
Hb4O8.
The reaction is rapid, requiring less than 0.01
second.
The deoxygenation (reduction) of Hb4O8 is also
very rapid.
8
Basic Concepts:
Oxygen Capacity (氧容量）: The maximum quantity
of oxygen that will combine chemically with the
hemoglobin in a unit volume of blood;
normally it amounts to 1.34 ml of O2 per gm of Hb or
20 ml of O2 per 100 ml of blood.
Oxygen Content（氧含量）: how much oxygen is in
the blood
Oxygen Saturation （血氧饱和度）: A measure of
how much oxygen the blood is carrying as a
percentage of the maximum it could carry
9
The oxygen-hemoglobin dissociation curve:
（氧离曲线）
the curve
relating
percentage
saturation of
the O2-carry
power of
hemoglobin to
the PO2.
10
The oxygen-hemoglobin dissociation curve
A. Flattened upper portion
B. Steep middle portion
C. Lower portion
11
Shifting the Curve
12
Factors that Shift the OxygenHemoglobin Dissociation
Curve
13
1. pH and PCO2: Bohr effect
14
2. Temperature
15
3. 2,3-diphosphoglycerate, 2,3,-DPG
(2, 3-二磷酸甘油）
A byproduct of anaerobic glycolysis.
Present in especially high concentration in red blood
cells because of their content of 2,3-DPG mutase.
The affinity of hemoglobin for O2 diminishes as the
concentration of 2,3-DPG increase in the red blood
cells.
16
Importance:
The normal DPG in the blood …
Hypoxic condition that last longer than
a few hours…
Disadvantage:
The excess DPG also makes it more
difficult for the hemoglobin to
combines with O2 in the lungs.
17
4. Effect of Carbon Monoxide (CO)
CO combines Hb at the same point as does O2,
and can displace O2 from hemoglobin.
CO binds with about 250 times as much tenacity
as O2.
Therefore, a PCO only a little greater than 0.4
mmHg can be lethal.
In the presence of CO (low concentration), the
affinity of hemoglobin for O2 is enhanced,
18
Effect of CO & Anemia on Hb-O2 affinity
Normal blood with Hb=15 gm/dl, anemia with Hb=7.5 gm/dl,
and normal blood with 50% COHb (carboxyhemoglobin).19
5. Fetal Hemoglobin
Advantage
Increased O2
release to the
fetal tissues
under the
hypoxic
condition.
20
II Carbon Dioxide Transport
Method
• Dissolved in Plasma
• Chemically Bound to
Hemoglobin in RBC’s
• As Bicarbonate Ion in
Plasma
Percentage
7 - 10 %
20 - 30 %
60 -70 %
Dissolved
bound to Hb
HCO3-
21
Carbaminohemoglobin
Formation
• Carbon dioxide molecule reversibly attaches to
an amino portion of hemoglobin.
CO2 + Hb
HbCO2
22
Carbonic Acid Formation
• The carbonic anhydrase stimulates water
to combine quickly with carbon dioxide.
CO2 + H2 0
H2 CO3
23
Bicarbonate Ion Formation
• Carbonic acid breaks down to release a
hydrogen ion and bicarbonate.
H2 CO3
H+ + HCO-3
24
CO2 Transport and Cl- Movement
25
Carbon Dioxide Dissociation Curve
Haldane effect
For any given PCO2,
the blood will hold
more CO2 when the
PO2 has been
diminished.
Reflects the
tendency for an
increase in PO2 to
diminish the affinity
of hemoglobin for
CO2.
26
Mechanism of Haldane effect
Combination of oxygen with hemoglobin in the
lungs cause the hemoglobin to becomes a
stronger acid. Therefore:
1) The more highly acidic hemoglobin has less
tendency to combine with CO2 to form CO2
Hb
2) The increased acidity of the hemoglobin also
causes it to release an excess of hydrogen
irons
27
Interaction Between CO2 and O2 Transportation
1. Bohr effect
28
2. Haldane effect
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