Acid Base Balance, Animation.

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pH is an indicator of acidity.

The body’s blood pH is strictly regulated within a narrow range between 7.35 and 7.45.

This is because even a minor change in acidity may have devastating effects on protein stability

and biochemical processes.

Normal cellular metabolism constantly produces and excretes carbon dioxide into the blood.

Carbon dioxide combines with water to make carbonic acid which dissociates into hydrogen

ions and bicarbonate.

This is an equilibrium, meaning all the components of the left and right sides co-exist at all

times, and the concentration of any component is determined by that of others at any given


The rule of thumb is: an increase in concentration of ANY component on ONE side will shift the

equation to the OTHER side, leading to INCREASED concentrations of all components on THAT side,

and vice versa.

This equilibrium is central to understand acid-base regulation.

CONTINUED carbon dioxide production by all cells of the body drives the equilibrium to

the right to generate more hydrogen ions.

Because pH is basically a function of hydrogen ion concentration, more hydrogen means higher

acidity and lower pH.

Normal metabolism, therefore, constantly makes the blood more acidic.

The body must react to keep the blood pH within the normal limits.

This is achieved by 2 mechanisms: - Elimination of carbon dioxide through exhalation.