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 Heart rate and resting breathing rate Blood plasma Red blood cell production and number of blood capillaries Haemoglobin Hb has 4 subunits, each subunit contains 2 parts Haem → ring of atoms linked to Fe2+ Globin → polypeptide chain Sequence of amino acids affects O2 carrying properties Oxyhaemoglobin HbO2 from lungs dissociates in respiring tissues 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 Biconcave disc → larger surface area to volume ratio for diffusion 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 CO2 + H2O → H2CO3(carbonic acid) → H+ + HCO3- (hydrogen carbonate) In red blood cells, carbonic anhydrase is present Rate of HCO3- production is higher than in blood plasma Establishes a conc gradient → HCO3- diffuses into plasma 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 More CO2 binds to haem when O2 conc is low Control Of Blood pH Dissociation of CO2 produces H+ ions Buffer keeps pH constant Plasma contains phosphate and plasma proteins Red blood cells contain Hb Hb takes up H+ and releases O2 to respiring tissues H+ + HbO2 → Hb + O2 The more H+ taken up by Hb the more O2 is released Higher rate of respiration produces more CO2 from respiring tissues More H+ is produced and taken up by Hb More O2 is released, therefore, more CO2 is transported in blood plasma Carbamino-haem travels to gas exchange surface There, more CO2 is removed and more O2 is taken up by haem More O2 is transported and supplied to respiring tissues Thus, CO2 regulates breathing rate The Oxyhaemoglobin Dissociation Curve % saturation of Hb is plotted against partial pressure of O2 (pO2) pO2 is a measure O2 concentration 100% saturation of Hb → high partial pressure → in lungs Low pCO2 as it is removed from the body → high O2 uptake O2 is transported to and unloaded in tissues 60% saturation (straight line) in muscles → using up O2 carried by Hb S-shaped because each Hb carries 4 molecules of O2 First molecule changes shape of Hb → remaining molecules bind more easily It becomes easier for the second and third molecules to bind Curve becomes flat at the end as binding of the last O2 is more difficult again The Bohr Effect Increased pCO2 moves dissociation curve to the right (Bohr shift) causes Hb to give up more O2 to respiring tissues pO2 falls (increase of respiration), more CO2 is released and rises pCO2 Curve to the right of the normal for active animals Small animals → low surface area to volume ratio → readily lose heat Higher metabolism increases metabolic rate This requires more O2 for respiration to generate ATP pO2 is high at respiring tissues as it comes directly form lungs pCO2 must have a high value as well (see above) O2 is released at high pO2 Curve to the left of the normal (greatest affinity for O2) pO2 is low in deep underground levels and high altitudes Fast release of O2 at low pO2 is required (Hb can adapt) Blood at placenta has low pO2 Fetus lives in low pO2 Fetal Hb has a high affinity for oxygen/is saturated at low pO2 Mother gives up O2 and fetus picks it up Fetus takes up O2 in limited supply Red pigment myoglobin stores O2 In muscles/anaerobic/diving animals → when O2 will get very low Fast release of O2 at very low pO2, but storage of O2 at high pO2 In some children fetal Hb is abnormally high / oxygen not released from fetal Hb/ in low pO2/body tissues/muscles / more anaerobic respiration / less ATP available / muscle fatigue