BIOL 2020U Lecture Notes - Fetus, Myoglobin, Partial Pressure

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29 Jan 2013
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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
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