ACIDOSIS
Acidosis is the reduction in pH
(increase in H+
concentration)
below normal range.
Acidosis is produced
by:
1. Increase in partial
pressure of CO2 in the body fluids particularly in
arterial blood
2. Decrease in HCO3 – concentration.
ALKALOSIS
Alkalosis is the increase in pH
(decrease in H+
concentration)
above the normal range.
Alkalosis is produced
by:
1. Decrease in partial
pressure of CO2 in the arterial blood
2. Increase in HCO3– concentration.
Since the partial
pressure of CO2 (pCO2) in arterial blood
is controlled by lungs, the acid-base disturbances produced
by the change in arterial pCO2 are called the respiratory disturbances.
On the other hand, the
disturbances in acid-base status produced by the change in HCO3 – concentration
are generally called the metabolic
disturbances.
Thus the acid-base
disturbances are:
1. Respiratory
acidosis
2. Respiratory
alkalosis
3. Metabolic acidosis
4. Metabolic
alkalosis.
RESPIRATORY ACIDOSIS
Respiratory acidosis
is the acidosis that is caused by alveolar hypoventilation. During hypoventilation
the lungs fail to
expel CO2,
which is produced in the tissues. CO2 is the major end
product of oxidation of
carbohydrates, proteins and fats. water
to form carbonic acid, which is called respiratory acid. Carbonic
acid dissociates into H+
and HCO3 –. The increased H+ concentration in blood leads to decrease
in pH and acidosis. Normal
partial pressure of CO2 in arterial blood is about
40 mm Hg. When it increases above 60 mm Hg acidosis occurs.
Causes of Excess CO2 in the Body
Hypoventilation (decreased
ventilation) is the primary cause for excess CO2 in
the body. Some of the conditions when increase in pCO2 and respiratory
acidosis occur due to hypoventilation.
RESPIRATORY ALKALOSIS
Respiratory alkalosis is
the alkalosis that is caused by alveolar hyperventilation. Hyperventilation causes
excess loss of CO2 from
the body. Loss of CO2 leads to decreased formation of carbonic acid
and decreased release of H+. Decreased H+ concentration
increases the pH leading to respiratory alkalosis.
When the partial
pressure of CO2 in arterial blood decreases
below 20 mm Hg, alkalosis occurs.
Causes of Decrease in
CO2
in
the Body
Hyperventilation is
primary cause for loss of excess CO2 from
the body because during hyperventilation, lot of CO2 is expired through
respiratory tract leading to decreased pCO2.
METABOLIC ACIDOSIS
Metabolic acidosis is
the acid-base imbalance characterized
by excess accumulation of organic acids
in the body, which is caused by
abnormal metabolic processes. Organic acids such as lactic acid,
ketoacids
and uric acid are formed by normal metabolism. The quantity of these acids increases
due to abnormality in the metabolism.
Causes of Metabolic
Acidosis
Lactic acid
The amount of lactic acid increases
during anaerobic glycolysis in some abnormal conditions such as
circulatory shock. Ketoacids The
amount of ketoacids increases because of insulin deficiency
as in the case of diabetes mellitus. In diabetes mellitus, glucose is not utilized
due to lack of insulin. So, lipids are utilized for liberation
of energy
resulting
in production of excess acetoacetic acid and beta hydroxybutyric acid.
Uric acid
The amount of uric acid increases in
the body due to the failure of excretion. Normally uric acid is excreted by
kidneys. But in renal diseases, the kidneys fail to excrete the uric acid.
METABOLIC ALKALOSIS
Metabolic alkalosis is
the acid-base imbalance caused by loss of excess H+ resulting in increased HCO3– concentration.
Some of the endocrine disorders, renal tubular disorders, etc. cause metabolic
disorders leading to loss of H+. It increases HCO3– and pH in the body leading to
metabolic alkalosis.
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