| MadSci Network: General Biology |
Hi Josh, As you may already know, pH is a measure of the concentration of H+ ions in a liquid. When a pH value is lower than 7.0, the concentration of H+ ions is high and the solution is termed acid. Inversely, if the pH value is higher than 7.0, the concentration of H+ ions is low, and the solution is termed basic, or alcaline. The concentration of H+ ions, hence pH, is a VERY important factor in any enzymatic reaction. One enzyme may work well at pH 4 while another works better at pH 8. We, however, have evolved from a marine organism that floated in salted water many millions of years ago. This organism was, obviously, alive and had already a lot of enzymes and proteins working to make sure that it could get enough energy from its environment to reproduce and survive. As this organism comes from the ocean, all of its enzymes were accustomed to work at a pH near that of the ocean (this goes back to bacterias and microscopic algae that live in water near the shore of oceans). This is why some say that blood pH is the same as the ocean (and concentrations of salt and other electrolytes is also highly similar to that of the ocean... explaining the salty taste of blood). As evolution is a process that keeps the good and scraps the bad, it tried to shape new things while keeping what worked well. In this case the enzymes that did so well for the early organisms were mostly kept and the conditions to make them work dictated which new enzymes were kept and which were not. Over millions of year of evolution, with the appearance of lizards, dinosaurs and mammals, blood pH remained somewhat a constant ensuring that every biochemical reactions that has to occur in order to keep you alive at each second (and there is a lot) CAN occur. If the blood pH increase or decrease by even a tenth of a pH unit (0.1 pH), the body will immediately try to correct the situation as the homeostasis (which dictates life) of the organism is in critical danger. The three mechanisms that act if there is a deregulation of pH are the chemical buffers present in the blood (bicarbonate/carbonic acid, monosodium phosphate/bisodium phosphate, proteins/proteinates), the respiratory center of the cerbral trunk (which, by increasing or decreasing breathing will alter the concentration of carbonic acid in the blood) and the regulation of water and ions retention by kidneys. All those mechanisms ensure that blood pH does not change (or so little) in order to keep YOU alive. Now if blood pH increase too much (higher than 7.8), the organism will become surexcited (mainly because the neurons of the brain have too much facility to conduct their signals... even if they should not!) and enter a tetanic and convulsive state which will easily lead to death. On the opposite side, if the pH drops too much (below 7.0), the organism become catatonic then comatose and then die (mainly because neurons cannot conduct their signals). Many physiological manifestations occur that will make you know that there is a problem with your blood pH. If you hyperventilate, because of an anxiety attack for example, you will decrease CO2 concentration in the blood which in turn will cause a direct increase in pH (soluble CO2 is transformed in carbonic acid in the blood... no more CO2, no more carbonic acid... hence pH increase!). This drop in pH will be detected by your brain and it will try to shut the blood circulation to your brain in order to try to limit the damages... the result? You faint! After fainting, you will resume normal breathing because the reflex breathing will kick in so that CO2 concentration and pH in the blood will return to normal. You then wake up feeling better. I hope this answered your question. Try to read about it on the web or in biology books... there are many more examples on how blood pH variations can have direct physiological effects in order to try to return things to normal (ie. keeping homeostasis). Ciao! Mike
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