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 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 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 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 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 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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