Blood Gas Transport
Dr Taha Sadig Ahmed
Physiology Dept College of Medicine
King Saud University
Riyadh
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• Oxygen and Carbon Dioxide Transport
Objectives :
At the end of this lecture the student is expected to :
Understand the forms of oxygen transport in the blood, the
importance of each.
Differentiate between O2 capacity, O2 content and O2
saturation.
Describe (Oxygen- hemoglobin dissociation curve)
Define the P50 and its significance.
How DPG, temperature, H+ ions and PCO2 affect affinity of
O2 for Hemoglobin and the physiological importance of
these effects.
Describe the three forms of carbon dioxide that are
transported in the blood, and the chloride shift.
• Transport of O2 and CO2 in body and body fluids
• O2 is mostly transported in the blood bound to
hemoglobin
• If the PO2 increases Hb binds O2
• If PO2 decreases Hb releases O2
• O2 binds to the heme group on hemoglobin,
with 4 oxygens /per Hb molecule
• Terminology (1)
• O2 content: amount of O2 ( in ml ) carried by 100 ml blood ( arterial or
venous ).
• When blood is 100 % saturated wit oxygen , as in the pulmonary
capillary, each ml of Hb carries 1.34 ml of oxygen ; therefore oxygen
content would be 15 gm Hb x 1.34 = 20 ml oxygen carried by 100 ml
blood ( because Hb concentration = 15 gm per 100 ml blood ).
• But when blood is only 75% saturated ( as in pulmonary artery) , each
100 ml blood contains 19.4 ml oxygen ( per 100 ml blood) .
• Amount of oxygen released from Hb in the tissues = 5 ml oxygen from
each 100 ml blood .
• There fore, oxygen content of venous blood =( 19.4 – 5 ) = 14.4 ml
oxygen per 100 ml blood
• During strenuous exercise , the oxygen uptake by the tissues increases
3 folds to become  15 ml O2/100 ml blood ; so the oxygen content of
venous blood during strenuous exercise = ( 19.4 – 15 ) = 4.4 ml oxygen
per 100 ml blood
• At rest the tissues consume 250ml O2 and produce 200 ml CO2 .
The Oxyhemoglobin Dissocaiation Curve
100% saturation , 20 ml
content ( in rterial blood )
75% saturation , 15 ml content ( in
pulmonary artery i.e,. venous
blood)
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• (A) at rest ,
amount of O2 given up ( oxygen uptake , unloaded ) at the tissues = 5
mlO2/100 ml blood
Therefore , what remains in venous blood = (20-5) =
15 ml O2 / 100 ml blood
• (B) During severe /strenuous exercise ,
During strenuous ( severe) exercise the oxygen uptake ( extraction ) by
the tissue increases 3 folds ( from 5 ml to 15 ml )  so 15 ml O2 is
extracted by the tissues from each 100 ml of blood
Therefore , what remains in is  venous blood will contain ( 20 -15 ml ) =
5ml O2 /100 ml blood .
• At rest, tissues consume 250 ml O2 /min and produce
200 ml CO2/min .
• Oxygen Transport in Blood
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3% dissolved in plasma
97% bound to hemoglobin (oxyhemoglobin)
Higher PO2 results in greater Hb saturation.
The relation between PO2 and Hb-O2 is described by Oxyhemoglobin
Saturation Curve , which is not linear ( straight line ) but Sigmoid
• ( s-shaped )
• It is not linear but sigmoid (S- shaped) in shape (S- shaped)
• Normal P50 = 26.5 mmHg
Oxyhemoglobin Dissociation Curve Right and Left Shifts
Right shift means  the oxygen is unloaded from Hb ( Hb
giving away O2 ) to the tissues from Hb,
Left shift means  loading or attachment of oxygen to
Hb .
The P 50 and curve shifts
P50:The arterial PO2 at which 50% of the Hb is
saturated with O2, normally P50= 26.5
The position of the dissociation curve can be determined
by measuring the P50
Decreased P50 means increased affinity of Hb to O2 or
shift of the curve to left
Increased P50 means decreased affinity of Hb to O2 or
shift of the curve to right.
Factors that shift the curve to the right are 
(1) increased blood H+ ( Arterial blood pH , PHa)
(2) increased PCO2 ( arterial blood pCO2 , PaCO2) {  which
will also lead to (1) }
(3) increased temperature ,
(4) increased blood 2,3 DPG
2,3-DPG is an organic phosphate present in human RBCs . It
binds to deoxyhaemoglobin  thus lowering Hb affinity for
oxygen  facilitates O2 removal from Hb  facilitating O2
deivery to the tissues ..
2,3 DPG increases in the RBCs in anemia and hypoxemia, and
thus serves as an important adaptive response in maintaining
tissue oxygenation
Fetal Hb: has a P50 of 20 mmHg in comparison to 27 mmHg
of adult Hb.
Factors that shift the curve to the left are
(1) decreased blood H+
(2) decreased increased PCO2
(3) decreased temperature ,
(4) decreased blood 2,3 DPG
of the dissociation curve during exercise
Exercise increases Temp, H+, 2,3 DPG and shift the
curve to right (Rt) .
Transport of Oxygen in the dissolved state
Only 3% of O2 is transported in the dissolved state,
at normal arterial PO2 of 95 mmHg , about 0.29 ml of
oxygen is dissolved in each 100ml of blood.
When the PO2 of the blood falls to 40 mmHg in tissue
capillaries, only 0.12 of oxygen remains dissolved.
i.e 0.17 ml of oxygen is normally transported in the
dissolved state to the tissues per each 100 ml of blood
Combination of Hb with CO  displacement of oxygen
CO combines with Hb at the same point on the Hb
molecule as does oxygen,
it binds with Hb about 250 times as much as O2 (affinity
of Hb to CO is very high (250 times) that to O2.
It causes Lt shift of the O2-Hb curvev
Transport of Carbon Dioxide in Blood
carbon dioxide is transported in three forms.
(2) As bicarbonate ions  70 %
(3) As Carbaminohemoglobin ( combined with Hb) 
23%.
(3) Dissolved in plasdma  7%
Each 100 ml of blood carry 4 ml of CO2
Transport of Carbon Dioxide in Blood
CO2 is transported in blood in three forms :
(1) As bicarbonate ion  70 % of the total blood CO2
(2) As carbamino hemoglobin ( combined to Hb )  23 %
(3) Dissolved  7 % of the total blood CO2
Each 100 ml of blood carries 4 ml of CO2 from the tissues .
Formation of Bicarbonate and the
Chloride Shift
in the tissues
Q: What is the chloride shift ? It is diffusion of
chloride into the red blood cell when HCO3leaves it.
Exchange of bicarbonate ion (HCO3-) and
chloride ion (Cl-) across the membrane of red
blood cells in order to main electrical
neutrality
in the pulmonary capillaries
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• Haldane Effect
Removal of oxygen from Hb increases binding of carbon
dioxide to Hb .
In addition to enhancing removal of carbon dioxide from
oxygen-consuming tissues, the Haldane effect promotes
dissociation of carbon dioxide from hemoglobin in the
presence of oxygen .
In the oxygen-rich capillaries of the lung, this property
causes the displacement of carbon dioxide to plasma as lowoxygen blood enters the alveolus and is vital for alveolar gas
exchange
• Bohr Effect
Increased carbon dioxide  decreased Hb affinity for O2
 release of O2 fro Hb .
Conversely , a decrease in CO2  increased pH  resulting
in Hb binding more & more O2 .
• Respiratory Exchange Ratio (Respiratory Quotient ,
RQ )
• R = Rate of carbon dioxide output
Rate of oxygen uptake
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Normally it is 4/5= 82%
When Carbohydrate diet is used  R ( RQ) = 1
When fats only is used R ( RQ) =0.7
A person on normal ( mixed) diet RQ =0.82