Gas Transport in the Blood
Dr Shihab Khogali
Ninewells Hospital & Medical School, University of Dundee
 Understand the effect of
partial pressure on O2 and
CO2 carriage in the blood
 Understand the means of
O2 carriage in the blood
 Understand the oxygenhaemoglobin dissociation
curve and the significance
of its sigmoid shape
 Know the Bohr effect and
its significance in O2
liberation at tissue level
What is
This
Lecture
About?
 Understand the means of
CO2 carriage in the blood
 Know the Haldane effect
and its significance in the
uptake of CO2 and CO2
generated H+ at tissue
level; and CO2 liberation at
the lungs
See blackboard for detailed learning objectives
Atmospheric air
Alveoli
O2 Picked up by blood at the
lungs must be transported to
the tissues for cellular use
Pulmonary
circulation
Systemic
circulation
CO2 produced at tissues must be
transported to the lungs for
removal from the body
Oxygen Partial Pressures around the System
Air
PO2 kPa
20
Gas
Pulmonary
Capillary Arterial
Diffusion
10
Atmosphere
Tissues
 This means that if the
partial pressure in
the gas phase is
increased the
concentration of the
gas in the liquid
phase would increase
proportionally
 The partial pressure
of a gas in solution is
its partial pressure in
the gas mixture with
which it is in
equilibrium
What is the Effect of Partial
Pressure on Gas Solubility?
Henry’s Law
•Gaseous Phase
•Liquid Phase (gas in solution)
The amount of a given gas dissolve
in a given type and volume of liquid
(e.g. blood) at a constant
temperature is:
proportional to the partial pressure
of the gas in equilibrium with the
liquid
Dissolved Oxygen
 The O2 amount dissolved in blood is proportional to the
partial pressure (Henry’s Law)
 3ml O2 per litre of blood at a PO2 of 13.3 kPa
 Under Resting conditions (cardiac output 5L/min): 15 ml/min
of O2 is taken to tissues as dissolved O2
 Even at strenuous exercise (cardiac output of 30 L/min): 90
ml/min would be taken to tissues as dissolved O2
 Resting O2 consumption of our body cells is about
250ml/min
 O2 consumption may increase up to 25 folds during
strenuous exercise
– Clearly, another mechanism is involved in O2
transport in the blood.
Oxygen Transport in the Blood
 Most O2 in the blood is transported bound to haemoglobin
in the red blood cells
 Normal O2 concentration in the arterial blood is about 20 ml/100 ml
(200 ml per litre) at a normal arterial PO2 of 13.3 kPa and a normal
haemoglobin concentration of 15 grams/100 ml
 Percentage of O2 carried bound to haemoglobin = 98.5%
 Percentage of O2 carried in the dissolved form = 1.5%
(3 ml per litre at a PO2 of 13.3 kPa )
 O2 is present in the blood in two forms: (1) bound to
haemoglobin (2) physically dissolved (very little O2)
Oxygen binding to haemoglobin
 Haemoglobin can form a reversible combination with O2
 Each Hb molecule contains 4 haem groups
 Each haem group reversibly binds to one O2 molecule
 Haemoglobin is considered fully saturated when all the
Hb present is carrying its maximum O2 load
 The PO2 is the primary factor which determine the
percent saturation of haemoglobin with O2
5.3
8.0
Blood PO2 (kPa)
13.3
O2 concentration ml/100 ml
% Haemoglobin Saturation
Oxygen Haemoglobin Dissociation Curve
100
% Hb saturation
Total O2
20
O2 combined with Hb
Dissolved O2
0
0
0
PO2 (kPa)
13
O2 concentration (ml/100 ml)
Oxygen Haemoglobin Dissociation Curve
100
Hb =20
100
Hb =15
20
100
Hb =10
0
0
13
PO2 (kP)
0
0
0
% Hb saturation
O2 concentration (ml/100 ml)
Saturation
Oxygen binding of haemoglobin
Binding of one O2 to Hb increases the affinity of
Hb for O2
– co-operativity
– Sigmoid
Flattens where all sites are becoming occupied
Flat upper portions
means that moderate fall
in alveolar PO2 will not
much affect oxygen
loading
Steep lower part
means that the peripheral
tissues get a lot of
oxygen for a small drop
in capillary PO2
% Haemoglobin Saturation
Significance of Sigmoid
5.3
8.0
Blood PO2
(kPa)
13.3
Bohr Effect
A shift of the curve to the right:- The Bohr Effect
% Hb saturation
100
Increased release of
O2 by conditions at
the tissues
PCO2
[H+]
Temperature
2,3-Biphosphoglycerate
0
PO2
Off-loading of O2 at Tissues
Curve in arterial
conditions
O2 content (ml/10mls)
20
Curve in tissue
conditions
Additional O2 given up
10
Tissue O2 Tension
0
0
20
2.6
40
5.3
60
8.0
80
10.6
PO2 (mm Hg, kP)
Arterial O2 Tension
100
13.3
Means of CO2 Transport in the Blood
Solution (10%)
As Bicarbonate (60%)
As Carbamino compounds (30%)
(1) CO2 in Solution
Henry’s Law
Carbon dioxide about 20 times more
soluble than oxygen
About 10% of carried CO2 is in solution
(2) Bicarbonate:
Most CO2 is transported in the blood as bicarbonate
Bicarbonate is formed in the blood by:-
CO2 + H2O
CA
H2CO3
H+ + HCO-3
Carbonic Anhydrase
Occurs in red-blood cells
Bicarbonate Formation
Chloride shift
Capillary wall
-
Cl
+
CO2
-
H + HCO3
H2CO3
H+ + Hb
CA
H2O +
HbH
Red blood cell
(3) Carbamino Compounds
Carbamino compounds formed by combination
of CO2 with terminal amine groups in blood
proteins.
Especially globin of haemoglobin to give
carbamino-haemoglobin
Rapid even without enzyme
Reduced Hb can bind more CO2 than HbO2
CO2 concentration (ml/100ml)
CO2 Dissociation Curve
5.3
55
v-
PO2
13.3
PO2
a = CO2 content in arterial blood
v- = CO2 content in mixed venous blood
a
45
5.3
6.6
CO2 partial pressure (kP)
The Haldane Effect
Removing O2 from Hb increases
the ability of Hb to pick-up CO2 and
CO2 generated H+
The Boher effect and the haldane effect work in
synchrony to facilitate:
O2 liberation and uptake of CO2 & CO2 generated H+ at tissues
Summary of CO2 Transport in the Blood