of carbon dioxide and consequent loss of carbonic acid cause
respiratory alkalosis. Metabolic alkalosis is due to excessive
loss of hydrogen ions or gain of bases.
In respiratory acidosis carbon dioxide accumulates, so
this can result from factors that hinder pulmonary ventila-
. These include the following:
1. Injury to the respiratory center of the brainstem,
decreasing rate and depth of breathing.
2. Obstructions in air passages that interfere with air
movement into the alveoli.
3. Diseases that decrease gas exchange, such as
pneumonia, or those that reduce surface area of the
respiratory membrane, such as emphysema.
Any of these conditions can increase the level of car-
bonic acid and hydrogen ions in body ﬂ uids, lowering pH.
How does the respiratory system help regulate acid-base balance?
How do the kidneys respond to excess hydrogen ions?
How do the rates at which chemical and physiological buf
systems act dif
Chemical and physiological buffer systems ordinarily main-
tain the hydrogen ion concentration of body ﬂ
very narrow pH ranges. Abnormal conditions may disturb
the acid-base balance. For example, the pH of arterial blood
is normally 7.35–7.45. A value below 7.35 produces
A pH above 7.45 produces
Such shifts in the pH of
uids may be life threatening. A person usually cannot
survive if the pH drops to 6.8 or rises to 8.0 for more than a
(f g. 21.13)
Acidosis results from accumulation of acids or loss of bases,
both of which cause abnormal increases in the hydrogen ion
concentrations of body ﬂ uids. Conversely, alkalosis results
from a loss of acids or an accumulation of bases accompanied
by a decrease in hydrogen ion concentrations
(f g. 21.14)
The two major types of acidosis are
Factors that increase carbon dioxide
levels, also increasing the concentration of carbonic acid
(the respiratory acid), cause respiratory acidosis. Metabolic
acidosis is due to an abnormal accumulation of any other
acids in the body ﬂ
uids or to a loss of bases, including bicar-
bonate ions. Similarly, the two major types of alkalosis are
IF the pH oF arterial blood drops to 6.8 or rises to 8.0
For more than a Few hours, the person usually cannot survive.
ers act rapidly, while physiological
ers may require several minutes to several days to begin resisting a
change in pH.
First line of defense
against pH shift
Second line of
Normal pH range
Increased concentration of H
Decreased concentration of H
Acidosis results From accumulation oF acids or loss oF
bases. Alkalosis results From loss oF acids or accumulation oF bases.