Acids & Bases

ACIDS & BASES DR Vijay 1/12/2008

Acids & Bases • Acids are chemical substances that can donate protons in solutions. HCl, H2CO3 • Base is a substance that accepts protons or hydrogen ions. HCO3-,

Strong and weak acids & bases

• Strong acid is one that rapidly dissociates & releases large amount of H+ ions in solution. • Weak acids have less tendency to dissociate H+ • Strong base is one that reacts rapidly & strongly with H+ & therefore quickly removes these from a solution.

pH • pH of a solution is defined as the negative logarithm of hydrogen ion activity. • Normal pH of the body fluids is 7.35 – 7.45 • Arterial blood pH = 7.4 • Interstitial fluid & venous blood = 7.35 • pH < 7.35 – acidosis

Metabolic sources of acids Volatile acids

Fixed acids or non volatile acids

• Phosphoric acids • Sulfuric acids • Pyruvic acids • Lactic acids • Keto acids • Uric acids

• Physiological ly important volatile acid is carbonic acid H2CO3

Metabolic sources of bases

• Catabolism of few food materials produces bases. • Citrate salts of fruit juices may produce bicarbonate salt. • Deamination of amino acids produce ammonia.

Regulatory mechanisms against changes in hydrogen ion concentration of blood

3 mechanisms 2.Buffer system 3.The respiratory mechanisms 4.Renal mechanisms

What is Buffer? • Buffer is a mixture of a weak acid & a salt of its conjugate base. + Buffer + H    

Buffer system & their role in acid base balance • Prevents excessive changes in hydrogen ion concentration. • Reacts within a fraction of a second • E.g. Bicarbonate buffer Phosphate buffer Protein buffer

Bicarbonate buffer system • Most important extracellular buffer • Plays important role in maintaining blood pH • Regulated by kidney & lungs At pH 7.4 HCO /H CO •

Mechanism of action of bicarbonate buffer HCO3 +           -

+ H

              

Respiratory regulation Fall in pH ↓ Stimulation of chemoreceptors ↓ Hyperventilation ↓

Renal mechanism in acid base balance

• By maintaining the bicarbonate ion concentration (alkali reserve) in the plasma. • By formation &

4 key reactions 1.Exchange of H+ for Na+ of tubular fluid 2.Reabsorption of bicarbonate from tubular fluid 3.Excretion of H+ ion as NH4+ in the form of NH4Cl

Disorders of acid base balance

• Acidosis : accumulation of excess acid or loss of alkali from the body. • Alkalosis : accumulation of excess alkali or loss of acid from the body. • Metabolic acidosis & Metabolic alkalosis • Respiratory acidosis &