| What is a disassociation curve? | - Shows how saturated the haemoglobin is with oxygen at any given partial pressure
- Shows how affinity for oxygen varies |
| Different saturations meaning | - 100% saturation = every haemoglobin molecule is carrying maximum of 4 molecules of O2
- 0% saturation = no haemoglobin molecules are carrying O2 |
| Explaining the disassociation curve | - The graph is S-shaped because when haemoglobin combines with the first O2 molecule
- It alters its shape in a way to make it easier for other molecules to join too
- But as Hb starts to become saturated
- It gets harder for more O2 molecules to join |
| Describing the disassociation curve | - As a result, the curve has a steep bit in the middle where its easy for O2 molecules to join
- Shallow bits at each end where its harder
- When the curve is steep, a small change in pO2 causes a big change in amount of O2 carried by Hb |
| Different dissociation curves on graph | - The further to the left of the curve, the greater the affinity for O2, the easier it is to take up oxygen, but the harder it is to release oxygen
- The further to the right of the curve, the lower the affinity for O2, the harder it is to take up oxygen, but the easier it is to release oxygen |
| Partial pressure of oxygen | - pO2
- Measure of oxygen concentration
- The greater the concentration of dissolved O2 in cells, the higher the partial pressure
- Haemoglobin's affinity for oxygen varies depending on the pO2 |
| Low and high partial pressure of oxygen | - Higher it is, higher affinity for O2, higher saturation of O2
- Lower it is, lower affinity for O2, lower saturation of O2 |
| Unloading and loading in lungs with partial pressure of oxygen | - O2 enters the blood capillaries at the alveoli
- Alveoli have high pO2
- So O2 loads onto haemoglobin, forming oxyhaemoglobin
- When cells respire, use up O2
- Lowering pO2
- Red blood cells deliver oxyhaemoglobin to tissues
- Unloads O2
- Haemoglobin returns to lungs, picks up more O2 |
| Partial pressure of carbon dioxide | - pCO2 |
| Effects of carbon dioxide concentration | - CO2 reduces haemoglobin's affinity for oxygen |
| The Bohr effect | - The greater the concentration of CO2, the more readily the haemoglobin releases its oxygen
- Explains why the behaviour of haemoglobin changes in different regions of the body |
| The Bohr effect in terms of oxygen unloading (with graph) | - When cells respire they produce CO2, which raises the pCO2
- This increases rate of O2 unloading, dissociation curve shifts right
- The saturation of blood with O2 is lower for given pO2, so more O2 will be released |
