1. Gas Transport in the Blood
Dr Shihab Khogali
Ninewells Hospital & Medical School, University of Dundee

2. See blackboard for detailed learning objectives
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 oxygen-haemoglobin dissociation curve and the significance of its sigmoid shape
Know the Bohr effect and its significance in O2 liberation at tissue level
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
What is
This
Lecture
About?
See blackboard for detailed learning objectives

3. O2 Picked up by blood at the
Atmospheric air
O2 Picked up by blood at the
lungs must be transported to the tissues for cellular use
Alveoli
Pulmonary
circulation
Systemic
circulation
CO2 produced at tissues must be transported to the lungs for removal from the body

4. Oxygen Partial Pressures around the System
Air
Gas 20
Pulmonary
Capillary
Arterial
PO2 kPa
Diffusion 10
Atmosphere
Tissues

5. Henry’s Law What is the Effect of Partial Pressure on Gas Solubility?
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
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
Gaseous Phase
Liquid Phase (gas in solution)

6. 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.

7. 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)

8. 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

9. Oxygen Haemoglobin Dissociation Curve
% Haemoglobin Saturation
O2 concentration ml/100 ml
5.3
8.0
13.3
Blood PO2 (kPa)

10. Oxygen Haemoglobin Dissociation Curve
100
Total O2 20
O2 combined with Hb
O2 concentration (ml/100 ml)
% Hb saturation
Dissolved O2 13
PO2 (kPa)

11. Saturation O2 concentration (ml/100 ml) % Hb saturation PO2 (kP) 100
100
Hb =20
% Hb saturation
100
Hb =15 20
O2 concentration (ml/100 ml)
100
Hb =10 13
PO2 (kP)

12. 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

13. Significance of Sigmoid
O2 concentration ml/100 ml
5.3
13.3
Blood PO2 (kPa)
% Haemoglobin Saturation
8.0
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

14. Bohr Effect % Hb saturation
A shift of the curve to the right:- The Bohr Effect
100
Increased release of O2 by conditions at the tissues
% Hb saturation
PCO2
[H+]
Temperature
2,3-Biphosphoglycerate
PO2

15. Off-loading of O2 at Tissues
Curve in arterial
conditions 20
Curve in tissue
conditions
Additional O2 given up 10
O2 content (ml/10mls)
Tissue O2 Tension
Arterial O2 Tension 20
2.6 40
5.3 60
8.0 80
10.6
100
13.3
PO2 (mm Hg, kP)

16. Means of CO2 Transport in the Blood
Solution (10%)
As Bicarbonate (60%)
As Carbamino compounds (30%)

17. (1) CO2 in Solution Henry’s Law
Carbon dioxide about 20 times more soluble than oxygen
About 10% of carried CO2 is in solution

18. Bicarbonate: Most CO2 is transported in the blood as bicarbonate
Bicarbonate is formed in the blood by:- CA
Carbonic Anhydrase
CO2 + H2O
H2CO3
H+ + HCO-3
Occurs in red-blood cells

19. Bicarbonate Formation
Chloride shift
Capillary wall
Cl-
CO2 CA
H++
HCO3-
H2CO3
H2O +
H+ + Hb
HbH
Red blood cell

20. (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

21. CO2 Dissociation Curve PO2 PO2 CO2 concentration (ml/100ml)
5.3 55 a v -
PO2
13.3
CO2 concentration (ml/100ml)
a = CO2 content in arterial blood
v- = CO2 content in mixed venous blood 45
5.3
6.6
CO2 partial pressure (kP)

22. Removing O2 from Hb increases the ability of Hb to pick-up CO2 and
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

23. Summary of CO2 Transport in the Blood
Figure 13.30: Carbon dioxide transport in the blood.
Carbon dioxide (CO2) picked up at the tissue level is transported in the blood to the lungs in three ways: (1) physically dissolved, (2) bound to hemoglobin (Hb), and (3) as bicarbonate ion (HCO3−). Hemoglobin is present only in the red blood cells, as is carbonic anhydrase, the enzyme that catalyzes the production of HCO3−. The H+ generated during the production of HCO3− also binds to Hb. Bicarbonate moves by facilitated diffusion down its concentration gradient out of the red blood cell into the plasma, and chloride (Cl−) moves by means of the same passive carrier into the red blood cell down the electrical gradient created by the outward diffusion of HCO3−. The reactions that occur at the tissue level are reversed at the pulmonary level, where CO2 diffuses out of the blood to enter the alveoli.