Transport of Gas in the Blood


Oxygen is transported in the blood via haemoglobin. This plays a key part in delivering oxygen to areas where it is most needed effectively.

Haemoglobin

"Understand the structure of haemoglobin in relation to its role in the transport of respiratory gases, including the Bohr effect."
"Understand the oxygen dissociation curve of haemoglobin."
  • Globular protein
  • 4 polypeptide chains
  • Quaternary structure
  • Each chain contains 1 haem group
  • Hb + 4O2 = Hb(O2)
  • Oxygen will bind to haemoglobin when oxygen concentration is high (lungs).
  • Oxygen will disassociate when the surrounding area has a low oxygen concentration (cells).
  • Partial pressure is the force exerted by gases in a mixture.
At higher partial pressures (ie. when oxygen concentration is high) oxygen binds to haemoglobin. After haemoglobin has picked up one molecule of O2 its affinity for oxygen increases further.

However, at a lower partial pressures (ie. when oxygen concentration is low) oxygen dissociates from haemoglobin.

This data can be shown on an oxygen dissociation curve and the graph is sigmoidal in shape.

The Bohr Shift

This shift explains how, in higher concentrations of CO2, haemoglobin more readily gives up oxygen.
  • At body cells that are respiring there is a high concentration of CO2.
  • This CO2 reacts with water to form carbanoic acid as shown below:
  • CO2 + H2O = HCO3- + H+
  • This acid lowers the pH, reducing HB's affinity for oxygen
  • This shifts the curve to the right (The Bohr Shift)
  • This is good for respiring cells as haemoglobin more easily releases oxygen which can be used for respiration.
  • Note that increasing the temperature actually reduces Hb's affinity for oxygen therefore shifting the curve to the right.

Fetal Haemoglobin & Myoglobin

"Understand the similarities and differences between the structures and functions of haemoglobin and myoglobin."
"Understand the significance of the oxygen affinity of fetal haemoglobin as compared to adult haemoglobin."
Fetal Haemoglobin
  • Has a higher affinity for oxygen than adult haemoglobin
  • This allows it to bind with oxygen that already has a reduced partial pressure
  • This allows both the mother and the child's oxygen needs to be met
Myoglobin
  • Only contains one haem group
  • Has a very high affinity for oxygen, even at low partial pressures
  • It is found in muscle cells where it is used as an energy store
  • Useful in mammals with high metabolic demands (eg: whales)