1. ACID BASE
BALANCE

2. • All the physiological activities depend upon the acid-base status of the body.
• An acid is the proton donor (the substance that liberates hydrogen ion).
• A base is the proton acceptor (the substance that accepts hydrogen ion).
• Hydrogen ion (H+) is highly reactive.
• The H+ shows severe effects on the physiological activities of the body even
at Acid-base Balance low concentrations.

3. • The normal H+ concentration in the extracellular fluid (ECF) is 38 to 42
nM/L.
• An increase in H+ ion concentration decreases the pH (acidosis) and a
reduction in H+ concentration increases the pH (alkalosis).
• A slight change in pH below 7.38 or above 7.42 will cause serious threats to
many physiological functions.

4. • The pH of arterial blood is an indirect measurement of H+ concentration
and it reflects the balance of CO2 and HCO3–.

5. REGULATION OF ACID BASE BALANCE:
• Two types of acids are produced in the body:
1. Volatile acid
2. Non-volatile acids
• Volatile acids are derived from CO2. Large quantity of CO2 is produced
during the metabolism of carbohydrates and lipids.
• Non-volatile acids are produced during the metabolism of other nutritive
substances such as proteins.

6. Compensatory mechanism:
• The body has three different mechanisms to regulate acid-base status:
1. Acid-base buffer system, which binds free H+
2. Respiratory mechanism, which eliminates CO2
3. Renal mechanism, which excretes H+ and conserves the bases (HCO3–).

7. Acid Base Buffer System:
• Buffer system is the one, which acts immediately to prevent the changes in pH.
Buffer system maintains pH by binding with free H+.
Types of Buffer Systems
• Body fluids have three types of buffer systems, which act under different
conditions:
1. Bicarbonate buffer system
2. Phosphate buffer system
3. Protein buffer system.

9. Bicarbonate Buffer System:
HCl + NaHCO3 → H2CO3 + NaCl
↓
CO2 + H2O
• This buffer system plays an important role in maintaining the pH of body
fluids than the other buffer systems.

10. • Concentration of HCO3– is regulated by kidney and the concentration of
CO2 is regulated by the respiratory system. These two regulatory
mechanisms operate constantly and simultaneously, making this system more
effective.

11. Phosphate Buffer System
• Phosphate buffer system is useful in the intracellular fluid (ICF).
• The concentration of phosphate is more in ICF than in ECF.
• HCl + Na2HPO4 → NaH2PO4 + NaCl
(strong acid) (weak acid)
• NaOH + NaH2PO4 → NaHPO4 + H2O
(strong base) (weak base)

12. • Phosphate buffer system is more powerful than bicarbonate buffer system as
it has a pK of 6.8, which is close to the pH of the body fluids, i.e. 7.4.

13. Protein buffer System
• Protein buffer systems are present in the blood; both in the plasma and
erythrocytes.
• Protein buffer systems in plasma are more powerful because of their high
concentration in plasma and because of their pK being very close to 7.4.
• Hemoglobin has about six times more buffering capacity than the plasma
proteins.

14. • The deoxygenated hemoglobin is a more powerful buffer than oxygenated
hemoglobin because of the higher pK.
• Hemoglobin prevents fall in pH when more and more CO2 enters the
capillaries.

15. Respiratory Mechanism
• When metabolic activities increase, more amount of CO2 is produced in the
tissues and the concentration of H+ increases.
• Increased H+ concentration increases the pulmonary ventilation
(hyperventilation) by acting through the chemoreceptors.
• Due to hyperventilation, the excess of CO2 is removed from the body.

16. Renal Mechanism
• Kidney maintains the acid-base balance of the body by the secretion of H+
and by the retention of HCO3–

17. DISTURBANCES
OF ACID-BASE STATUS
• The acid-base disturbances are:
1. Respiratory acidosis
2. Respiratory alkalosis
3. Metabolic acidosis
4. Metabolic alkalosis.

18. • Normal partial pressure of CO2 in arterial blood is about 40 mm Hg. When
it increases above 60 mm Hg acidosis occurs.