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Natural Buffers
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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Update: June 2012
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