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Carriage of respiratory Gases By Y Stock Objectives You should be able to: Describe the structure of erythrocytes. Describe the role of respiratory pigments. Understand curves. and interpret dissociation WWW.NIM.NIH.GOV Red blood cells Biconcave discs 8 micrometers diameter No nucleus Made in bone marrow Destroyed by liver/spleen Function: To carry oxygen and carbon dioxide Adaptions: Shape gives a large surface area, encouraging diffusion Full of haemoglobin www.astrographics.com/.../Display/GP2120.jpg Haemoglobin www.chemsoc.org/.../LearnNet/cfb/images/13A.jpg Haemoglobin Consists of 4 polypeptide chains, each with an iron containing haem group. Each haem group combines with an oxygen molecule Haemoglobin+oxygen=oxyhaemoglobin Hb + 4O2 = HbO8 Reversible reaction www.scientific-art.com/.../Haemoglobin.gif Hb + 4O2 = HbO8 High partial pressure oxygen Lungs Oxyhaemoglobin formed Low partial pressure oxygen Active tissues Oxyhaemoglobin breaks down Oxygen released Oxygen dissociation curves Found by exposing haemoglobin to air mixtures of varying oxygen partial pressures and determining its % saturation. www.jcu.edu/biology/RESPS.JPG S shaped curve Over the steep section a small fall in Oxygen partial pressure causes a sizeable drop in % saturation. The curve shows that: at relatively low oxygen concentrations there is uncombined haemoglobin in the blood and little or no oxyhaemoglobin, e.g. in body tissue at relatively high oxygen concentrations there is little or no uncombined haemoglobin in the blood; it is in the form of oxyhaemoglobin, e.g. in the lungs. Effect of increased carbon dioxide Bohr Effect Curve shifted to right Increased CO2 causes oxyhaemoglobin to unload some of its oxygen. www.coheadquarters.com/Bohr1.gif Fate of carbon dioxide 7-10% dissolves in plasma 20-30% in red cells as carbaminohaemoglobin (binds to amino acids) 60-70% plasma converted to bicarbonate in Conversion to bicarbonate Carbon dioxide diffuses into red cells Enzyme:carbonic CO2 anhydrase + H2O = H2CO3 This dissociates H2CO3 = H+ + HCO3- HCO3- diffuses into plasma H+ combine with oxyhaemoglobin forming haemoglobinic acid. H+ + HbO2 = HHB + O2 Oxygen displaced. Haemoglobin buffering pH changes www.colprado.edu/.../image/figure13g.jpg Myoglobin -Curve shifted to left Myoglobin oxygen. Oxygen PO2 binds more tightly to only given up at very low Images.encarta,msn.com/…/cha/00076b5f.gif Quiz Haemoglobin quiz image search RSC