Gas Transport in the Blood
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Transcript of Gas Transport in the Blood
Gas Transport in the BloodGas 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 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 LectureAbout?
See blackboard for detailed learning objectives
O2 Picked up by blood at the lungs must be transported to the tissues for cellular use
CO2 produced at tissues must be transported to the lungs for removal from the body
Pulmonarycirculation
Systemiccirculation
Alveoli
Atmospheric air
Oxygen Partial Pressures around the System
20
Atmosphere Tissues
10
Air
Gas PulmonaryCapillary
Diffusion
Arterial
PO
2 k
Pa
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
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)
What is the Effect of Partial Pressure on Gas Solubility?
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
Oxygen Haemoglobin Dissociation Curve
O2 c
on
cen
trat
ion
ml/
100
ml
5.3 13.3
Blood PO2 (kPa)
% H
aem
og
lob
in S
atu
rati
on
8.0
% H
b s
atu
rati
on
0
100
O2 c
once
ntr
ati
on (
ml/1
00
ml)
0
20
PO2 (kPa)
Total O2
O2 combined with Hb
Dissolved O2
0 13
Oxygen Haemoglobin Dissociation Curve
Saturation
PO2 (kP)
0 13O2 c
once
ntr
ati
on (
ml/1
00
ml)
0
20
% H
b s
atu
ratio
n
0
100Hb =15
100
0
Hb =10
0
100Hb =20
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
Significance of Sigmoid
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 O
2 c
on
cen
trat
ion
ml/
100
ml
5.3 13.3
Blood PO2
(kPa)
% H
aem
og
lob
in S
atu
rati
on
8.0
Bohr Effect
% H
b s
atu
rati
on
PO2
PCO2
[H+]
Temperature
2,3-Biphosphoglycerate0
100
A shift of the curve to the right:- The Bohr Effect
Increased release of O2 by conditions at the tissues
Off-loading of O2 at Tissues
O2 c
onte
nt
(ml/1
0m
ls)
00
405.3
202.6
608.0
8010.6
10013.3
PO2 (mm Hg,
kP)
20
10
Arterial O2 Tension
Tissue O2 Tension
Curve in arterialconditions
Curve in tissueconditions
Additional O2 given up
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 H2CO3 H+ + HCO-3
CA
Carbonic Anhydrase
Occurs in red-blood cells
Bicarbonate Formation
Red blood cell
Capillary wall
CO2
H2O +H2CO3CA
HCO3
-H++
Cl-
Chloride shift
H+ + Hb HbH
(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 Dissociation Curve
5.3 6.6
CO
2 c
on
cen
trat
ion
(m
l/10
0ml)
45
55
CO2 partial pressure (kP)
PO2
5.3
13.3
a
v-
PO2
a = CO2 content in arterial bloodv- = CO2 content in mixed venous blood
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