Transport of oxygen

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  • Transport of oxygen
    • Heamoglobin
      • Quaternary structure, consists of 4 polypeptide chains with a heam group at the centre of each chain
      • Each heam group contains an iron atom, one O2 binds to each iron
      • Can bind with 4 O2 molecules
        • 4 binding steps. Each time O2 is added, H+ is removed to produce Hb(O2)4
    • Oxygen dissociation curve
      • S shaped
      • 4 stages
        • 1: high O2 concentration in lungs, so O2 binds, haem becomes 100% saturated.
        • 2: In muscle, liver & brain, O2 is used for respiration so concentrations low so haem is only 50% saturated as it unloads half to the cells
        • 3: In tissues respiring quickly (contracting muscles) PO2 drops further so saturation is only at around 10% almost 90% is unloaded
        • 4: respiring tissue also produce CO2 which dissolves in tissue fluid, lowering the pH, which reduces saturation, (shown by dotted line) the Bohr effect. Saturation is at around 5%, so 95% of O2 is unloaded to respiring tissue
    • Different haemoglobins
      • Fetus
        • Higher affinity for O2 at low PO2, curve is shifted up
        • Different ahem allows O2 to diffuse from the mothers blood to the fetes into fettle tissue
      • Lugworm
        • Live in the mud where the O2 concentration can fall very low as it respires
        • Very high affinity for O2 so the curve is shifted ups they can obtain O2 when PO2 is very low
      • Mouse
        • Lose heat very quickly due to large SA:Vol. ratio so they have a high metabolic rate to generate more heat
        • Higher demand for O2, so the curve is shifted down so plenty of O2 is consistently unloaded


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