Carriage of Oxygen

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  • Carriage of Oxygen
    • Haemoglobin
      • +oxygen ---> oxy-haemoglobin
        • oxy-haemoglobin must be able to dissociate with oxygen to release it into respiring cells
      • complex protein with 4 sub-units consisting of a polypetide chain and a haem group
        • each haem group contains an iron ion (2+) that can attract and hold an oxygen molecule - has an affinity for it
    • Oxygen Transport
      • amount of oxygen is measured by the relative pressure that it contributes to a mixture of gases - PARTIAL PRESSURE/ pO2/OXYGEN TENSION - measured in kPa
      • oxy-haemoglobin dissociation curve - S shape
        • at low oxygen tensions, the haemoglobin does not readily take up oxygen molecules because the haem groups that attract the oxygen are in the centre of the molecule
          • accounts for the low saturation level of haemoglobin at low oxygen tensions
        • as oxygen tension rises, the diffusion gradient into the haemoglobin molecule increases, so one oxygen molecule diffuses into the haemoglobin molecule, causing a conformational change in the shape
          • allows more oxygen molecules to diffuse into the haemoglobin
            • accounts for  the steepness of the curve as the oxygen tension rises
        • once the haemoglobin contains 3 oxygen molecules, it becomes more difficult for the 4th to diffuse in - so it is difficult to achieve 100% oxygen saturation
    • Fetal Haemoglobin
      • has a higher affinity for oxygen than adult haemoglobin
      • must be able to pick up oxygen when adult haemoglobin releases it
      • must absorb oxygen from the mothers blood, reducing the oxygen tension within the blood fluid, making the maternal haemoglobin release oxygen
        • so the fetal dissociation curve is to the left of the adults


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