2. Compensatory mechanisms
for Metabolic Acidosis
The body regulates the acidity of the blood by
four buffering mechanisms:
• Bicarbonate buffering system
• Intracellular buffering system
• Respiratory compensation
• Renal compensation
3. Bicarbonate buffering system
The bicarbonate buffering system is an
important buffer system in the acid-base
homeostasis.
In this system, carbon dioxide (CO2) combines
with water to form carbonic acid (H2CO3),
which in turn rapidly dissociates to form
hydrogen ions and bicarbonate (HCO3- )
The carbon dioxide - carbonic acid equilibrium
is catalyzed by the enzyme carbonic
4. Intracellular buffering
by absorption of hydrogen atoms by
various molecules, including proteins,
phosphates and carbonate in bone.
5. Respiratory Compensation of
Metabolic Acidosis
is a mechanism by which plasma pH
can be altered by varying the
respiratory rate. It is faster than renal
compensation, but has less ability to
restore normal values
In the case of Metabolic Acidosis
chemoreceptors sense a deranged
acid-base system, and there is
increased breathing
6. Renal Compensation of
Metabolic Acidosis
the kidney produces and excretes
ammonium (NH4+) and
monophosphate, generating
bicarbonate in the process while
clearing acid
8. Respiratory compensation - occurs mainly in
the lungs, which retain CO2 through slower
breathing, or hypoventilation (respiratory
compensation). CO2 is then consumed toward
the formation of the carbonic acid intermediate,
thus decreasing pH.
The decrease in [H+] suppresses the peripheral
chemoreceptors, which are sensitive to pH. But,
because respiration slows, there's an increase in
PCO2 which would cause an offset of the
depression because of the action of the central
chemoreceptors which are sensitive to the partial
pressure of CO2[citation needed] in the cerebral
spinal fluid. So, because of the central
chemoreceptors, respiration rate would be
increased.
Renal compensation - consists of increased
excretion of HCO3- (bicarbonate), as the
filtered load of HCO3- exceeds the ability of the
renal tubule to reabsorb it.
9. Compensatory Mechanisms of
Respiratory Acidosis
In acute respiratory acidosis, compensation
occurs in 2 steps :
1. The initial response in cellular buffering
that occurs over minutes to hours. Cellular
buffering elevates plasma bicarbonate only
slightly
2. The second step is renal compensation
that occurs over 3-5 days. With renal
compensation, renal excretion of carbon is
acid is increased and bicarbonate
reabsorption is increased.
11. Compensatory Mechanisms of
Respiratory Alkalosis
Compensation in an Acute Respiratory
Alkalosis :
Changes in the physicochemical equilibrium
occur due to the lowered pCO2 and this results in
a slight decrease in HCO3-. There is insufficient
time for the kidneys to respond so this is the only
change in an acute respiratory alkalosis. The
buffering is predominantly by protein and occurs
intracellularly; this alters the equilibrium position
of the bicarbonate system.
12. Compensatory Mechanisms of
Respiratory Alkalosis
Compensation in a Chronic Respiratory
Alkalosis :
Renal loss of bicarbonate causes a further fall in
plasma bicarbonate (in addition to the acute drop
due to the physicochemical effect and protein
buffering).
