transport of oxygen and carbon dioxide in the blood
Transport of Oxygen:
- Erythrocytes (RBCs) carry oxygen in the blood.
- They are a biconcave shape, so there is a greater SA:V for diffusion.
- They have no nuclei, so space for oxygen is maximised.
- They have prosthetic haem groups, which have a high affinity for oxygen and combine reversibly to oxygen to absorb it/release it.
- When erythrocytes enter the lung capillaries, they are deoxygenated so there is a steep concentration gradient so the diffusion rate is high.
- When oxygen diffuses into erythrocytes, it forms a compound called oxyhaemoglobin (as it binds with the haemoglobin). This also maintains a steep concentration gradient so diffusion rate into the cell remains high.
- The formula for the reversible reaction of haemoglobin and oxygen into oxyhaemoglobin is as follows:
Oxygen Dissociation Curve:
- Shows how oxygen affinity (and thus its % oxygen saturation) changes with partial pressure.
- Should always form an s-shaped (sigma) graph.
- Higher partial pressure, means a faster uptake of oxygen as it is more readily available, so there is a higher % oxygen saturation.
- In the lungs, there is high PPoO, and this steep concentration gradient causes a rapid loading of oxygen into hameoglobin.
- In the body, there is a drop in PPoO in the tissues, so this causes a rapid offloading of oxygen.
Key Terms
- Partial Pressure (of Oxygen): The concentration of oxygen in a mixture of gases, e.g. the air.
- Bohr Effect: as partial pressure of carbon dioxide rises, haemoglobin gives away more oxygen(because haemoglobin is designed to give oxygen to respiring tissues).
- If an oxygen dissociation curve is displaced the left, it has a higher affinity. This means it loads oxygen readily, but offloads less readily.
- E.G. Foetal haemoglobin has a higher affinity for oxygen than it's mother's haemoglobin as it needs to steal the oxygen form the mothers blood.
- E.G. Animals that live at high altitudes (llamas) have higher affinity because there is less oxygen available.
- If an oxygen dissociation curve is displaced to the right it had lower affinity. This means it loads oxygen slower, but offloads readily.
- E.G. Animals that live near sea level (lugworms) because there is more oxygen available.
Transport of Carbon Dioxide:
- 5% is dissolved in the blood plasma.
- 10-20% combines with amine groups in the haemoglobin's polypeptide chains, forming carbaminohaemoglobin.
- 75-85% forms hydrocarbonate ions (HCO3-) in the cytoplasm of the erythrocytes.
- The formula is as follows:
Movement of carbon dioxide into and out of haemoglobin:
Key Terms
Chloride Shift: Where bicarbonate ions move out of the RBC in exchange for
chloride ions. Both ions have the same charge, and this maintains the electrical balance of the cell.