GAS TRANSPORT
OXYGEN(O2)
&
CARBONDIOXIDE(CO2)
Gas Transport
• O2 which is taken up by the blood at the lungs
is transported to the tissues for use by the
cells.
• CO2 produced at the cell level is transported to
the lungs for elimination.
2
Oxygen (O2) Transport
• Most of the O2 in the blood is transported
bound to hemoglobin.
Method of O2 Transport
• Chemically bound to Hemoglobin – 98.5%
• Physically Dissolved in plasma
– 1.5%
3
Oxygen Transport
• Most O2 in the blood is transported bound to
hemoglobin.
Method of O2 Transport
• Chemically bound to Hemoglobin – 98.5%
• Physically Dissolved in plasma
– 1.5%
4
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Oxygen Transport
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Hb is present inside red blood cells [RBC].
Hb is iron bearing protein molecule.
It makes reversible combination with oxygen.
When Hb combines with O2, we call
Oxyhemoglobin [HbO2].
• Hb + O2  HbO2
• When O2 not combined with Hb, we call it
reduced Hemoglobin or Deoxyhemoglobin.
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Gas Transport
Hemoglobin promotes the net transfer of oxygen at
both the alveolar and tissue levels.
• There is a net diffusion of oxygen from the alveoli to the
blood. This occurs continuously until hemoglobin is as
much saturated as possible (97.5% at PO2 of100 mm of
Hg).
• At the tissue cells hemoglobin rapidly delivers oxygen
into the blood plasma and on to the tissue cells. Various
factors promote this unloading.
Factors producing unloading of O2:
• An increase in carbon dioxide from the tissue cells into
the systemic capillaries increased hemoglobin
dissociation from oxygen (shifts the dissociation curve
to the right).
• Increased acidity has the same effect.
This shift of the curve to the right (more dissociation)
is called the Bohr effect.
• Higher temperatures also produces this shift, as does
the production of BPG.
• Hemoglobin has more affinity for carbon monoxide
as compared to oxygen.
CO POISONING
• Hemoglobin has more affinity for carbon
monoxide(240 times) as compared to
oxygen.
• CO a poisonous gas, liberated by burning
of carbon products, eg. automobile
gasoline, coal, wood & tobacco.
• Not detected, because it is colorless,
odorless & non irritating and may be
lethal.
Oxygen-Hemoglobin (O2-Hb)
dissociation(or saturation) curve
Factors at the tissue level promoting
the unloading of O2 from Hb
(Summary)
• Shifting of O dissociation curve to right or more
dissociation [giving] of O2 to tissues or less affinity
of O2 for Hb.
• The factors are
1- Increase PCO
2- Increase Acidity [increase H+ ion]
3- Increase Temperature
4- Increase 2,3-BPG [bisphosphoglycerate] or
2,3-DPG [diphosphoglycerate]
2
2
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CO2 Transport
• CO2 is transported in the blood by three ways:
1. Physically dissolved in Plasma- 10%
2. Bound to Hb- 30% Carbamino-Hb(Hb-CO2)
3. As Bicarbonate- 60%
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CO2 Transport
Most carbon dioxide (about 60%) is transported as the Bicarbonate Ion.
• Carbon dioxide combines with water to form carbonic acid.
– The enzyme carbonic anhydrase facilitates this in the erythrocyte.
– Carbonic acid dissociates into hydrogen ions and the bicarbonate ion.
• 2-step, reversible process is favored at the tissue cells.
– The reverse of this process (bicarbonate ions forming free molecules of
carbon dioxide) occurs in the lungs.
• 30% of the carbon dioxide is bound to hemoglobin in the blood. This is
another means of transport.
• About 10% of the transported carbon dioxide is dissolved in the plasma.
Gas Transport
Most carbon dioxide (about 60%) is transported as the
Bicarbonate Ion.
• By the chloride shift, the plasma membrane of the erythrocyte
passively facilitates the diffusion of bicarbonate ions (out of the red
cell) and chloride ions (inside of the red cell).
• By the Haldane effect the removal of oxygen from hemoglobin at
the tissue cells increases the ability of hemoglobin to bind with
carbon dioxide.
Abnormalities in Arterial PO2
Hypoxia
• Condition of having insufficient O2 at the cell level
• Categories
– Hypoxic hypoxia (low arterial blood PO2) eg. high altitude,
inadequate gas exchange
– Anemic hypoxia (reduced O2 carrying capacity of blood) eg. Less
RBC /Hb, CO poisoning
– Circulatory hypoxia(too little oxygenated blood is delivered to
tissue); Stagnant hypoxia eg. congestive heart failure or circulatory
shock
– Histotoxic hypoxia (inability of cells to use O2) eg. cyanide
poisoning
Hyperoxia
• condition of having an above-normal arterial PO2
• Can only occur when breathing supplemental O2
• Can be dangerous
Abnormalities in Arterial PCO2
• Hypercapnia
– Condition of having excess CO2 in arterial blood
– Caused by hypoventilation
• Hypocapnia
– Below-normal arterial PCO2 levels
– Brought about by hyperventilation which can be
triggered by
• Anxiety states
• Fever
• Aspirin poisoning
Things to be learn from this lecture
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Gas transport
Methods of O2 transport
Role of hemoglobin (Hb)in O2 transport
O2-Hb dissociation curve
Factors affecting Hb-O2 dissociation curve
Methods of CO2 transport
Abnormalities of PO2 & PCO2