Some oxygen can be transported dissolved in plasma but this is minor (only 3% of oxygen transport). Most oxygen is transported bound to haemoglobin. haemoglobin + oxygen = oxyhaemoglobin . Each haemoglobin molecule can transport four oxygen molecules. When oxygen molecules are bound to haemoglobin they are said to be associated . When they are released they are said to be disassociated . The ODC
The reaction where haemoglobin takes up oxygen occurs when the concentration of oxygen is high (e.g. in the lung capillaries) And… the reverse reaction where the oxygen is released occurs when the concentration of oxygen is low (e.g. in the muscle capillaries). The ODC
Unfortunately the transport of oxygen is not simple because temperature & CO 2 concentration also effect the ability of haemoglobin to carry O 2 . Plus the fact that haemoglobin does not simply accept oxygen at high concentration and release it at low concentration it does so in a non linear fashion. The association and disassociation of oxygen from haemoglobin can be described with a sigmoidal graph. This graph is known as the oxyhaemoglobin dissociation curve. The ODC
This graph shows when the partial pressure of oxygen is high ( as it is in the lung capillaries ) there is a very high saturation of haemoglobin with oxygen. When the partial pressure of oxygen is low ( as it is in the capillaries of the tissues ) there is a low saturation of haemoglobin with oxygen... This means the haemoglobin releases oxygen as it travels from the lungs to the tissues. The ODC
The amount of oxygen carried and released by haemoglobin depends not only on the partial pressure of oxygen but also on pH. An increase in carbon dioxide causes a decrease in pH. An acidic environment causes oxygen to dissociate from haemoglobin. Just a small decrease in the pH results in a large decrease in the percentage saturation of the haemoglobin with oxygen. This shift of the curve is called the Bohr effect . The ODC
Examiners tip. “This graph can be used to explain the following points (remember [ ] = concentration:)
There is high [O2] in the lungs and low [CO2]
The haemoglobin will therefore be virtually saturated with O2.
In tissues (actively respiring) there will be low [O2] and high [CO2]
The haemoglobin will therefore give up a lot of the O2 that it is transporting
A fetus developing in the uterus must be able to extract oxygen from its mother’s blood. Fetal haemoglobin therefore requires a higher affinity for oxygen than adult haemoglobin (it combines more readily with oxygen). Myoglobin is a pigment found in muscles which acts as an oxygen store and it receives its oxygen from haemoglobin therefore it also has a high affinity for oxygen. The ODC
The higher the temperature, the less saturated the blood is with oxygen. This situation often arises during exercise (heat is produced by respiration in muscle cells) The increased temperature causes haemoglobin to release oxygen more readily. The ODC
Quick quiz – haemoglobin has increased affinity for oxygen – which way does the curve shift?
Quick quiz – haemoglobin of an animal that lives at high altitude would it be to the left or right of this curve?
Use Figure 1 to describe how haemoglobin loads and unloads oxygen in the body.
Loading of oxygen at high p.p. oxygen / in lungs; Unloads oxygen at low p.p. oxygen / in tissues;
Explain the advantage of the shape and position of the llama’s dissociation curve.
Picks up oxygen more readily (in lungs) / greater affinity / idea of more readily saturated ; Where partial pressure of O 2 is low ;