Page 208 - 84 human physiolofy part-1

Chapter 11

involuntarily increase breathing rate very soon after beginning the sprint. You will continue to breathe
heavily after the race, thus expelling more carbon dioxide, until pH has returned to normal.

Regulation of Blood pH

Many of us are not aware of the importance of maintaining the acid/base balance of our blood. It is
vital to our survival. Normal blood pH is set at 7.4, which is slightly alkaline or "basic". If the pH of
our blood drops below 7.2 or rises above 7.6 then very soon our brains would cease functioning
normally and we would be in big trouble. Blood pH levels below 6.9 or above 7.9 are usually fatal if
they last for more than a short time. Another wonder of our amazing bodies is the ability to cope with
every pH change – large or small. There are three factors in this process: the lungs, the kidneys and
buffers.

So what exactly is pH? pH is the concentration of hydrogen ions (H+). Buffers are molecules
which take in or release ions in order to maintain the H+ ion concentration at a certain level. When
blood pH is too low and the blood becomes too acidic (acidosis), the presence of too many H+ ions is
to blame. Buffers help to soak up those extra H+ ions. On the other hand, the lack of H+ ions causes
the blood to be too basic (alkalosis). In this situation, buffers release H+ ions. Buffers function to
maintain the pH of our blood by either donating or grabbing H+ ions as necessary to keep the number
of H+ ions floating around the blood at just the right amount.

The most important buffer we have in our bodies is a mixture of carbon dioxide (CO2) and
bicarbonate ion (HCO3). CO2 forms carbonic acid (H2CO3) when it dissolves in water and acts as an
acid giving up hydrogen ions (H+) when needed. HCO3 is a base and soaks up hydrogen ions (H+)
when there are too many of them. In a nutshell, blood pH is determined by a balance between
bicarbonate and carbon dioxide.

Bicarbonate Buffer System. With this important system our bodies maintain homeostasis. (Note
that H2CO3 is Carbonic Acid and HCO3 is Bicarbonate)

CO2 + H2O <---> H2CO3 <---> (H+) + HCO3

• If pH is too high, carbonic acid will donate hydrogen ions (H+) and pH will drop.
• If pH is too low, bicarbonate will bond with hydrogen ions (H+) and pH will rise.

Too much CO2 or too little HCO3 in the blood will cause acidosis. The CO2 level is increased
when hypoventilation or slow breathing occurs, such as if you have emphysema or pneumonia.
Bicarbonate will be lowered by ketoacidosis, a condition caused by excess fat metabolism (diabetes
mellitus).

Too much HCO3 or too little CO2 in the blood will cause alkalosis. This condition is less common
than acidosis. CO2 can be lowered by hyperventilation.

So, in summary, if you are going into respiratory acidosis the above equation will move to the
right. The body's H+ and CO2 levels will rise and the pH will drop. To counteract this the body will
breathe more and release H+. In contrast, if you are going into respiratory alkalosis the equation will
move to the left. The body's H+ and CO2 levels will fall and the pH will rise. So the body will try to
breathe less to release HCO3. You can think of it like a leak in a pipe: where ever there is a leak, the

208 | Human Physiology