824
UNIT FIVE
respiratory alkalosis
and
metabolic alkalosis.
Excessive loss
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-
tion
(f
g. 21.15)
. 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.
PRACTICE
25
How does the respiratory system help regulate acid-base balance?
26
How do the kidneys respond to excess hydrogen ions?
27
How do the rates at which chemical and physiological buf
er
systems act dif
er?
21.6
ACID-BASE IMBALANCES
Chemical and physiological buffer systems ordinarily main-
tain the hydrogen ion concentration of body fl
uids within
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
acidosis.
A pH above 7.45 produces
alkalosis.
Such shifts in the pH of
body fl
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
few hours
(f g. 21.13)
.
Acidosis
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
respiratory acidosis
and
metabolic acidosis.
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
FIGURE 21.13
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.
FIGURE 21.12
±Chemical±buf
ers act rapidly, while physiological
buf
ers may require several minutes to several days to begin resisting a
change in pH.
Chemical
buffer system
Bicarbonate
buffer system
Phosphate
buffer system
Protein
buffer system
Respiratory
mechanism
(CO
2
excretion)
Renal
mechanism
(H
+
excretion)
First line of defense
against pH shift
Physiological
buffers
Second line of
defense against
pH shift
7.35
Survival range
Normal pH range
pH scale
7.45
8.0
7.0
6.8
7.8
Acidosis
Alkalosis
pH rises
pH drops
Increased concentration of H
+
pH scale
7.4
Acidosis
Accumulation
of acids
Loss of
bases
Alkalosis
Decreased concentration of H
+
Accumulation
of bases
Loss of
acids
FIGURE 21.14
Acidosis results From accumulation oF acids or loss oF
bases. Alkalosis results From loss oF acids or accumulation oF bases.
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