Applied Physiology – Disturbances Of Acid-Base Status

| Home |

Chapter: Anatomy, Physiology And Health Education : Acid-Base Balance

Acidosis is the reduction in pH (increase in H+ concentration) below normal range





Acidosis is the reduction in pH (increase in H+ concentration) below normal range.


Acidosis is produced by


1.  Increase in partial pressure of CO2  particularly in arterial blood

2.  Decrease in HCO – concentration.




Alkalosis is the increase in pH (decrease in H+ concentration) above the normal range (Table 5.2).


Alkalosis is produced by:


1.   Decrease in partial pressure of CO2 in the arterial blood

2.   Increase in HCO – 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 HCO 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.


CO2 accumulates in blood where it reacts with water to form carbonic acid, which is called respiratory acid. Carbonic acid dissociates into H+ and HCO . 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 are listed in Table 5.3.





Respiratory alkalosis is the alkalosis  that  is  caused by alveolar hyperventilation. Hyperventilation causes excess loss of CO2 from the body. Loss of COleads  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. Some of the conditions when decreased pCO2 and respiratory alkalosis occur due to hyperventilation are given in Table 5.4.





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.




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.


Some of the conditions when the metabolic acids increase in the body resulting in metabolic acidosis are listed in Table 5.3.








Metabolic alkalosis is the acid-base imbalance caused by loss of excess H+ resulting in increased HCO concentration. Some of the endocrine disorders, renal tubular disorders, etc. cause metabolic disorders leading to loss of H+. It increases HCO and pH in the body leading to metabolic alkalosis.



Some of the conditions when excess H+ is lost and HCO content increases leading to metabolic alkalosis are given in Table 5.4.


Copyright © 2019, 2020; Developed by Therithal info.