Transcript Part 4 Oxygen and carbon dioxide transport in blood

Part 4 Oxygen and Carbon
Dioxide Transport in Blood
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Basic Mechanism
Two forms of the gases: physical dissolution and
chemical combination.
Most of O2 and CO2 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
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I. Transport of Oxygen
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Oxygen Transport
• Method
Percentage
• Dissolved in Plasma
1.5 %
• Combined with Hemoglobin
98.5 %
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Oxygen
Bound to Hgb
Dissolved
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Hemoglobin Structure
Protein made up of 4 subunits
Every subunit contains a heme moiety attached to a
polypeptide chain.
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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
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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
Normal Value: 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）: The
percentage of all the available heme binding sites
saturated with oxygen
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The oxygen-hemoglobin dissociation curve:
（氧离曲线）
the curve
relating
percentage
saturation of
the O2-carry
power of
hemoglobin to
the PO2.
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The oxygen-hemoglobin dissociation curve
A. Flattened upper portion
B. Steep middle portion
C. Lower portion
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Shifting the Curve
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Factors that Shift the
Oxygen-Hemoglobin
Dissociation Curve
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1. pH and PCO2: Bohr effect
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2. Temperature
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3. 2,3-diphosphoglycerate, 2,3,-DPG
(2, 3-二磷酸甘油）
A byproduct of anaerobic glycolysis.
Present in high concentration in red blood cells
because of their content of 2,3-DPG mutase (变位
酶）.
Diminishes the affinity of hemoglobin for O2
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Importance:
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.
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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.
PCO greater than 0.4 mmHg can be lethal.
In the presence of CO (low concentration), the
affinity of hemoglobin for O2 is enhanced
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5. Fetal Hemoglobin
Advantage
Increased O2
release to the
fetal tissues
under the
hypoxic
condition.
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II Carbon Dioxide Transport
Method
• Dissolved in Plasma
Percentage
7 - 10 %
• Chemically Bound to
Hemoglobin in RBC’s
20 - 30 %
• As Bicarbonate Ion in
Plasma
60 -70 %
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Carbon Dioxide
Dissolved
bound to Hb
HCO3-
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Carbaminohemoglobin （氨基甲
酰血红蛋白） Formation
• Carbon dioxide molecule reversibly attaches to
an amino portion of hemoglobin.
CO2 + Hb
HbCO2
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Carbonic Acid Formation
• The carbonic anhydrase stimulates water
to combine quickly with carbon dioxide.
CO2 + H2 0
H2 CO3
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Bicarbonate Ion Formation
• Carbonic acid breaks down to release a
hydrogen ion and bicarbonate.
H2 CO3
H+ + HCO-3
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CO2 Transport and Cl- Movement
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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.
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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
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Interaction Between CO2 and O2 Transportation
1. Bohr effect
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2. Haldane effect
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