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Name: Shenal
Status: Student
Grade:  Other
Location: N/A
Country: United States
Date: October 2005


Question:
How is the pH of the blood controlled? What happens when the blood pH is not maintained?



Replies:
The pH of blood is controlled by a bicarbonate (H2CO3/HCO3-) buffer system. When the pH gets too high (high OH concentration), the OH- reacts with carbonic acid (H2CO3) to form HCO3- and H2O. When the pH gets too low (high H+ concentration), the H+ reacts with HCO3- to form H2CO3. Because H2CO3 is a weak acid, the H+ stays associated with the H2CO3. The definition of a buffer system is a chemical system consisting of a weak acid (in this case H2CO3) and a weak base (in this case bicarbonate ion = HCO3-). The HCO3- meets the definition of a base because it can accept a proton (H+) which keeps the proton from dissociating which would effectively lower the pH. When the pH gets too low (acidosis) or too high (alkalosis), many proteins and enzymes will become denatured (unfolded) which affects many diferent metabolic reactions. The normal pH of blood is around *7.4, and if it gets as low as 7.1 or as high as 7.7, these are pH's that would be life threatening. Remember that because pH is a log scale, a pH of 7.1 has twice the H+ concentration as a pH of 7.4, and, conversely, a pH of 7.7 has half the H+ concentration (or twice the OH- concentration) as a pH of 7.4. Recall that 0.301 if the log of 2.*

*Good luck,*

*Ron Baker, Ph.D.*


Blood pH is controlled by the amount of hydrogen ion (H+1) or hydroxyl ion (OH-1) in the blood. There are several physiological cycles that use/generate these species and several sources. One major cycle is the oxygen / CO2 exchange in respiration. We inhale O2 and exhale CO2. The presence of CO2 in the blood stream lowers the pH of the blood (makes it more acidic). A "google" search on the term "acidosis" got the following (of many) hits. Since pH is an important factor in many physiological processes, a change in the blood pH is a potentially life threatening condition requiring immediate regulation. The citations below (and others you will find) can provide the information you seek in as much detail as you desire. No doubt there are entire books, and certainly chapters, devoted to the subject of blood pH.

Vince Calder


http://www.nlm.nih.gov/medlineplus/ency/article/001181.htm http://www.nlm.nih.gov/medlineplus/ency/article/000335.htm

http://www.emedicine.com/emerg/topic312.htm

http://www.emedicine.com/emerg/topic291.htm


Your body has many ways to control blood pH. One is that it contains buffers; these are substances that resist drastic changes in pH. Also, when you breathe, you "blow off" carbon dioxide, which when it is dissolved in water (blood) becomes acidic. This is why, when someone is in cardiac or respiratory arrest, they administer bicarbonate which is basic. If you hyperventilate and blow off too much carbon dioxide, the treatment is to breathe into a paper bag, which actually allows you to re-breathe some carbon dioxide. As your kidneys filter your blood, they also take acid out of the blood and put it into the urine, which is why it is naturally slightly acidic. Those are the major mechanisms but there are others.

vanhoeck



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