Oxygen Transport
Topics covered:
Explain the role that O2 dissolved in water/plasma plays in transporting
the gas and why the low solubility of O2 limits the amount carried in
simple solution at usual partial pressures.
Describe the reaction between myoglobin (in muscle) and O2, and
sketch a curve showing how saturation of myoglobin varies with PO2.
Describe how myoglobin acts as a useful reservoir of O2 in red muscle.
Describe the successive reactions between a haemoglobin molecule
(in blood) and four O2 molecules, including the change in shape of the
haemoglobin molecule (allosterism) as it combines with the first O2
molecule.
Explain how the allosteric properties of haemoglobin lead to the
characteristic shape of O2/ haemoglobin dissociation curve.
Draw and label an O2/Hb dissociation curve at a PCO2 of 5 kPa (40
mm Hg), [H+] of 40 nM (pH 7.4), temperature of 37oC. Include the
following:
a) labelled axes with appropriate units and values, (b) alternative
ordinates (vertical axes) of % saturation and O2 content/ litre, (c)
typical point for arterial blood, (d) typical point for 90% saturated blood,
e) typical point for mixed venous blood, (f) the P50 of blood, (g) the line
passing through the origin.
Indicate how changes of temperature, PCO2 and [H+] alter the curve.
Hence explain the effect on the unloading of O2 as blood advances
down a capillary in exercising muscle.
Explain the origin of 2,3-DPG and its effect on the position of the
Hb/O2 dissociation curve. Name the conditions in which 2,3-DPG
concentration increases.
On the axes for the graph in bullet point 5, sketch a Hb/O2 curve for
fetal haemoglobin. With the help of this, explain the loading of fetal
blood with O2 at the placenta.
Demonstrate on two Hb/O2 dissociation curves -one with O2 content
and the other with O2 saturation as the ordinates- the effect of severe
anaemia on O2 carriage in blood.
Explain carbon monoxide poisoning in terms of the bond between CO
and Hb. Indicate the effect of CO on the O2/Hb dissociation curve.
Explain and distinguish the meaning of the terms 'oxygen partial
pressure', 'oxygen saturation' and 'oxygen content'.
How is oxygen transported?
Myoglobin and haemoglobin
Factors that modulate the shape of haemoglobin dissociation curve
2,3 Diphosphoglycerate
Other forms of haemoglobin
Important terms:
, Partial Pressure O2 (PO2)
O2 content
Saturation
Partial Pressure O2 (PO2)
Dry air is about 21% oxygen (O2) and about 79% nitrogen (N2). (So as an example, in
100 molecules, 79 would be nitrogen, 21 would be oxygen).
Avogadro’s law tells us that 1 mole of any gas occupies 22.4L
The pressure exerted by a gas is dependent on the number of molecules of that gas in a
given volume.
So, if atmospheric pressure (PB) is 100kPa (kilopascals) then –
N2 exerts 79% of this pressure – PN2 is 79kPa
O2 exerts 21% of this pressure – PO2 is 21kPa
PO2 can also be given as mmHg or Torr (commonly seen in American textbooks).
Partial pressure is important for three reasons:
1) It determines chemical activity
2) It determines rate of diffusion
3) It determines solubility
Fick’s law of diffusion-
Net diffusion of gas across semipermeable membrane = [area x (P1 – P2)/ distance] x
[solubility/ √molecular weight]
(P1-P2) = difference in pressure on either side of the membrane
So here it can be seen that partial pressures and solubility are important in how gases
move across the body
Remember that partial pressure of O2 is a measure of the amount of O2 dissolved in the
plasma.
(e.g. we left a bowl of water out in air, amount of O2 that would dissolve in it would be
at equilibrium with air, 21kPa
O2 Content
O2 content of is the:
Volume of gas (ml l-1) = solubility x partial pressure of the gas
Topics covered:
Explain the role that O2 dissolved in water/plasma plays in transporting
the gas and why the low solubility of O2 limits the amount carried in
simple solution at usual partial pressures.
Describe the reaction between myoglobin (in muscle) and O2, and
sketch a curve showing how saturation of myoglobin varies with PO2.
Describe how myoglobin acts as a useful reservoir of O2 in red muscle.
Describe the successive reactions between a haemoglobin molecule
(in blood) and four O2 molecules, including the change in shape of the
haemoglobin molecule (allosterism) as it combines with the first O2
molecule.
Explain how the allosteric properties of haemoglobin lead to the
characteristic shape of O2/ haemoglobin dissociation curve.
Draw and label an O2/Hb dissociation curve at a PCO2 of 5 kPa (40
mm Hg), [H+] of 40 nM (pH 7.4), temperature of 37oC. Include the
following:
a) labelled axes with appropriate units and values, (b) alternative
ordinates (vertical axes) of % saturation and O2 content/ litre, (c)
typical point for arterial blood, (d) typical point for 90% saturated blood,
e) typical point for mixed venous blood, (f) the P50 of blood, (g) the line
passing through the origin.
Indicate how changes of temperature, PCO2 and [H+] alter the curve.
Hence explain the effect on the unloading of O2 as blood advances
down a capillary in exercising muscle.
Explain the origin of 2,3-DPG and its effect on the position of the
Hb/O2 dissociation curve. Name the conditions in which 2,3-DPG
concentration increases.
On the axes for the graph in bullet point 5, sketch a Hb/O2 curve for
fetal haemoglobin. With the help of this, explain the loading of fetal
blood with O2 at the placenta.
Demonstrate on two Hb/O2 dissociation curves -one with O2 content
and the other with O2 saturation as the ordinates- the effect of severe
anaemia on O2 carriage in blood.
Explain carbon monoxide poisoning in terms of the bond between CO
and Hb. Indicate the effect of CO on the O2/Hb dissociation curve.
Explain and distinguish the meaning of the terms 'oxygen partial
pressure', 'oxygen saturation' and 'oxygen content'.
How is oxygen transported?
Myoglobin and haemoglobin
Factors that modulate the shape of haemoglobin dissociation curve
2,3 Diphosphoglycerate
Other forms of haemoglobin
Important terms:
, Partial Pressure O2 (PO2)
O2 content
Saturation
Partial Pressure O2 (PO2)
Dry air is about 21% oxygen (O2) and about 79% nitrogen (N2). (So as an example, in
100 molecules, 79 would be nitrogen, 21 would be oxygen).
Avogadro’s law tells us that 1 mole of any gas occupies 22.4L
The pressure exerted by a gas is dependent on the number of molecules of that gas in a
given volume.
So, if atmospheric pressure (PB) is 100kPa (kilopascals) then –
N2 exerts 79% of this pressure – PN2 is 79kPa
O2 exerts 21% of this pressure – PO2 is 21kPa
PO2 can also be given as mmHg or Torr (commonly seen in American textbooks).
Partial pressure is important for three reasons:
1) It determines chemical activity
2) It determines rate of diffusion
3) It determines solubility
Fick’s law of diffusion-
Net diffusion of gas across semipermeable membrane = [area x (P1 – P2)/ distance] x
[solubility/ √molecular weight]
(P1-P2) = difference in pressure on either side of the membrane
So here it can be seen that partial pressures and solubility are important in how gases
move across the body
Remember that partial pressure of O2 is a measure of the amount of O2 dissolved in the
plasma.
(e.g. we left a bowl of water out in air, amount of O2 that would dissolve in it would be
at equilibrium with air, 21kPa
O2 Content
O2 content of is the:
Volume of gas (ml l-1) = solubility x partial pressure of the gas
