Transcript Carriage of Oxygen - Mrs Miller's Blog

Carriage of Oxygen
• Describe the role of haemoglobin in
carrying oxygen
• Explain the differences between adult and
fetal haemoglobin
Haemoglobin
• Oxygen is transported in the red blood
cells (erythrocytes)
• These contain the protein haemoglobin
• When haemoglobin takes up oxygen it
becomes oxyhaemoglobin
Haemoglobin + oxygen  oxyhaemoglobin
Haemoglobin Structure
• A protein with 4 subunits
• Each subunit is made of a polypeptide chain (a protein) and a haem
group (non-protein)
• The haem group has a single iron atom Fe2+ that can hold an oxygen
molecule
• The haem group is said to have an attraction (affinity) for oxygen
• Each haemoglobin molecule can hold 4 oxygen molecules (one in
each subunit)
Taking up and Releasing oxygen
• Oxygen is absorbed
at the lungs as there
is a steep diffusion
gradient present
• Oxygen is released
(dissociated) at
respiring cells
Haemoglobin and oxygen transport
• The ability of haemoglobin to take up and
release oxygen depends on the amount of
oxygen present (the partial pressure or
pO2) It is also called the oxygen tension,
and is measured in units of pressure (kPa)
Dissociation curve
You would expect that if you doubles the
amount of oxygen, the amount taken up by
haemoglobin would also double, however
it does not behave like this.
Saturation of
haemoglobin
Concentration (partial pressure) of oxygen
S- shaped curve
• The oxyhaemoglobin dissociation curve is the s-shaped curve that
shows how saturated (full up) the haemoglobin molecules are at
different concentrations (partial pressures) of oxygen
Once the majority of haemoglobin
molecules have 3 oxygen
molecules, it is more difficult for the
4th to get in. This is why it is difficult
to get 100% saturation of
haemoglobin, even when the
oxygen concentration is really high
(like in the human lungs)
Saturation of
haemoglobin
Concentration (partial pressure) of oxygen
At low oxygen
concentrations, most of
the haem groups that
attract the oxygen
molecules are in the
centre of the haemoglobin
molecule, so less are fully
saturated (full with oxygen)
Fetal haemoglobin
absorbs oxygen from the
mothers blood fluid,
which reduces the
concentration of oxygen
making the mothers
haemoglobin release
some also
As the oxygen tension
(amount) rises, more
haemoglobin molecules have
gained their first oxygen,
meaning that it is now easier to
receive their second etc. (a
conformational change) so the
saturation of the molecules as
a whole rapidly increases