Equilibrium in Living Systems
There are numerous equilibrium systems in the human body which are essential to our
everyday functioning.
Case 1: Consider the equilibrium: haemoglobin + oxygen  oxyhaemoglobin
In an environment with a high oxygen concentration the equilibrium point is moved to
the right and lots of oxyhaemoglobin is produced. This occurs in your lungs. The
oxyhaemoglobin is then transported via your bloodstream to your bodies cells which
need the oxygen for respiration. In the cells there is a low concentration of oxygen
compared with oxyhaemoglobin and so the reverse reaction predominates, thereby
releasing the oxygen for use.
Case 2: Consider the equilibrium: haemoglobin + CO  CO-haemoglobin
This equilibrium system has a higher K value than the formation of oxyhaemoglobin
considered above. If CO is introduced to the lungs it will consume haemoglobin at
the expense of the oxyhaemoglobin reaction. A reduction in available haemoglobin
drives the reaction in case 1 backwards. With insufficient oxygen reaching brain cells
unconsciousness, or in severe cases death, results.
Case 3: Consider the equilibrium: CO2(g)  CO2(aq)
Carbon dioxide gas is a product of the respiration reaction in cells. As more CO2(g) is
produced it drives the CO2 into solution where it reacts with water in a two step
process.
CO2(aq) + H2O(l)  H2CO3(aq)  H+(aq) + HCO3-(aq)
The equilibrium constant lies well to the right for these reactions. When the HCO3reaches the lungs the reverse reaction predominates as it is a CO2 low concentration
environment.
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