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Haemoglobin and Hydrogen Carbonate

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BIOL 2020U

Haemoglobin and Hydrogen Carbonate Ions carry Respiratory Gases and Control Blood Ph Haemoglobin Transports Oxygen  Lower atm pressure / fewer molecules present / less O2 reaches tissues  Body adapts to changes by increasing o Heart rate and resting breathing rate o Blood plasma o Red blood cell production and number of blood capillaries  Haemoglobin Hb has 4 subunits, each subunit contains 2 parts o Haem → ring of atoms linked to Fe2+ o Globin → polypeptide chain o Sequence of amino acids affects O2 carrying properties  Oxyhaemoglobin HbO2 from lungs dissociates in respiring tissues o O2 diffuses into body cells while Hb is transported back to lungs  Features of red blood cells that allow them to transport O2 more efficiently o Biconcave disc → larger surface area to volume ratio for diffusion o Absence of nuclei/other organelles → more room for haemoglobin Hydrogen Carbonate Ions Remove CO2  CO2 produced in tissues diffuses into blood plasma  There it reacts with H2O in the plasma and in the cytoplasm of red blood cells o CO2 + H2O → H2CO3(carbonic acid) → H+ + HCO3- (hydrogen carbonate)  In red blood cells, carbonic anhydrase is present o Rate of HCO3- production is higher than in blood plasma o Establishes a conc gradient → HCO3- diffuses into plasma o Cl- diffuses into red blood cells to keep eqm in balance → chlorine shift  Thus, most CO2 is transported in blood as HCO3-  But, small amount reacts directly with haem to produce carbamino-haem o More CO2 binds to haem when O2 conc is low Control Of Blood pH  Dissociation of CO2 produces H+ ions  Buffer keeps pH constant o Plasma contains phosphate and plasma proteins o Red blood cells contain Hb  Hb takes up H+ and releases O2 to respiring tissues o H+ + HbO2 → Hb + O2 o The more H+ taken up by Hb the more O2 is released  Higher rate of respiration produces more CO2 from respiring tissues o More H+ is produced and taken up by Hb o More O2 is released, therefore, more CO2 is transported in blood plasma o Carbamino-haem travels to gas exchange surface o There, more CO2 is removed and more O2 is taken up by haem o More O2 is transported and supplied to respiring
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