Acid-Base Balance Nestor T. Hilvano, M.D., M.P.H.

Learning Objectives 1.Describe the bicarbonate, phosphate, and protein buffer systems. 2.Explain the compensatory mechanisms involved in the maintenance of acid-base balance. 3.Identify the types and causes of acidosis and alkalosis and describe their effects.

Acid-Base Balance Normal pH range of ECF is 7.35 to 7.45= __. ____ - lower pH ____ - raise pH Hydrogen Ions (H + ) - are gained at digestive tract and cellular metabolic activities; are eliminated at kidneys (urine) and at lungs ____ - resist changes in pH; bicarbonate, phosphate and protein systems a. bases b. buffers c. acids d. neutral

Bicarbonate Buffer System Solution of carbonic acid and bicarbonate ions –CO 2 + H 2 O  H 2 CO 3  HCO H + Reversible reaction important in ECF –CO 2 + H 2 O  H 2 CO 3  HCO H + lowers pH by releasing H + –CO 2 + H 2 O  H 2 CO 3  HCO H + raises pH by binding H +

Phosphate Buffer System H 2 PO 4 -  HPO H + –as in the bicarbonate system, reactions that proceed to the right release H + and  pH, and those to the left  pH Important in the ICF and renal tubules (urine) –where phosphates are more concentrated and function closer to their optimum pH of 6.8

Protein Buffer System More concentrated than bicarbonate or phosphate systems Acidic side groups (COOH) can release H + Amino side groups (NH2) can bind H + Important in both ECF and ICF

Respiratory Compensation of pH Respiratory activity has direct effect with carbonic acid- bicarbonate buffer system –CO 2 + H 2 O  H 2 CO 3  HCO H + lowers pH by releasing H + –CO 2 (expired) + H 2 O  H 2 CO 3  HCO H + raises pH by binding H +  CO 2 and  pH = stimulate pulmonary ventilation (RR)  CO 2 and  pH = inhibit pulmonary ventilation

Renal Control of pH Most powerful buffer system (but slow response) Renal tubules secrete H + into tubular fluid, then excreted in urine

Disorders of Acid-Base Balances Respiratory acidosis –Cause is hypoventilation –Results to increase CO2 –Acute respiratory acidosis is life –threatening –Chronic respiratory acidosis (emphysema, CHF, pneumonia) Respiratory alkalosis –Cause is hyperventilation –Results to decrease CO2 –Symptoms involve tingling sensations, light- headedness, loss consciousness

Disorders of Acid-Base Balances Metabolic acidosis –  production of organic acids (lactic acid, ketones seen in alcoholism, diabetes) –ingestion of acidic drugs (aspirin) –loss of base (chronic diarrhea, laxative overuse) Metabolic alkalosis (rare) –overuse of bicarbonates (antacids) –loss of acid (chronic vomiting)

Compensation for pH Imbalances Respiratory system adjusts ventilation (fast, limited compensation) –hypercapnia (  CO 2 ) = stimulates pulmonary ventilation –hypocapnia = inhibits pulmonary ventilation Renal compensation (slow, powerful compensation) –effective for imbalances of a few days or longer –acidosis causes  in H + secretion –alkalosis causes bicarbonate secretion

Homework (Self-Review) 1.Define terms: pH, acids, bases, buffer. 2.Identify and describe briefly the 3 major buffer systems. 3.Differentiate respiratory acidosis, respiratpry alkalosis, metabolic acidosis, and metabolic alkalosis. 4.Describe briefly the respiratory and renal compensations in response to changes in plasma pH.