Role of kidney in maintaining acid base balance (pH) by; Dr. Ashok Kumar J

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1. RENAL REGULATION OF pH Dr. Ashok Kumar J International Medical School Management and science university Malaysia Dr. Ashok Kumar J; IMS; MSU 10/20/2014 1

2. Dr. Ashok Kumar J; IMS; MSU Renal mechanism Kidney plays a major role in acid-base regulation 2. Reclamation the bicarbonate ions present in the ultra-filtrate 1. Excretion of H + 3. Excretion of titrable acid 4. Excretion of ammonia 10/20/2014 2

3. Dr. Ashok Kumar J; IMS; MSU Excretion of H + - Occurs in proximal tubule - CO 2 combines with H 2 O to form H 2 CO 3 - It dissociates to form HCO 3 - and H + - H + is secreted in exchange for Na + - Net production of HCO 3 - and net excretion of H + - mechanism serves to increase the alkali reserve HCO 3 - HCO 3 - H 2 O + CO 2 H 2 CO 3 - H + H + Tubular cell Tubular Lumen Na + Na + 10/20/2014 3

4. Dr. Ashok Kumar J; IMS; MSU HCO 3 - HCO 3 - H 2 O + CO 2 H 2 CO 3 - H + H + HCO 3 - + H 2 CO 3 - H 2 O CO 2 + CO 2 Tubular cell Tubular Lumen 2. Reclaimation the bicarbonate ions present in the ultrafiltrate 10/20/2014 4

5. Dr. Ashok Kumar J; IMS; MSU HCO 3 - H 2 O + CO 2 H 2 CO 3 - H + NH 4 + H + Tubular cell Tubular Lumen NH 3 Titrable acid Na 2 HPO 4 - NaH 2 PO 4 - GLUTAMIN GLUTAMATE Glutaminase NH 3 10/20/2014 5

6. Dr. Ashok Kumar J; IMS; MSU NH3 (ammonia) freely crosses the cell membrane enters the lumen of renal tubule Combines with protons present in the filtrate to form NH4 (ammonium ions) Ammonium ions are impermeable through the cell membrane – excreted in urine Daily excretion in urine 60 mEq /L of H+ excreted as Ammonia 10/20/2014 6

7. When there is an excess of acid production in the body, H + are excreted in urine as titrable acid and ammonia Titratable acidity of urine : The number of milliliters of N/10 (0.1N) NaOH required to titrate 1 liter of urine to pH 7.4. This is a measure of net acid excretion by the kidney Dr. Ashok Kumar J; IMS; MSU 10/20/2014 7

8. Dr. Ashok Kumar J; IMS; MSU Anion Gap In Extracellular fluid Sum of anions = Sum of cations - Electrical neutrality Sodium (Na+) and Potassium (K+) together accounts for 95 % of the cations Chloride and bicarbonate accounts for only 86% of the anions Measured cations Sodium 136 mEq/L Potassium 4 mEq/L Unmeasured Cation Calcium 4.5 mEq/L Magnesium 1.5 mEq/L Measured anions Chloride 98mEq/L Bicarbonate 25mEq/L Unmeasured anion Protein 15mEq/L Phosphate 2mEq/L Organic acids 5mEq/L Sulfate 1mEq/L 10/20/2014 8

9. Dr. Ashok Kumar J; IMS; MSU Unmeasured anions constitute the anion gap Calculated as difference between measured cations and measured anions Anion Gap = (Na + + K + ) - (Cl - + HCO 3 - ) Normal is about 12 mEq /L e.g : = ( 140 + 4) – (103 + 25) = 16 10/20/2014 9

10. Dr. Ashok Kumar J; IMS; MSU Disturbance in acid base balance Acidosis : Clinical state where acids accumulate or bases are lost Alkaosis : Clinical state where accumulation of base or loss of acids [Bicarbonate] pH = pKa + log 10 [Carbonic acid] 10/20/2014 10

11. Dr. Ashok Kumar J; IMS; MSU [Bicarbonate] [Carbonic acid] pH = pKa + log 10 Regulated by Kidney Metabolic component Decreased Bicarbonate Decreases the ratio Decreases pH Metabolic Acidosis ACIDOSIS Metabolic acidosis :- Primary alkali (bicarbonate) deficit 10/20/2014 11

12. Dr. Ashok Kumar J; IMS; MSU [Bicarbonate] [Carbonic acid] pH = pKa + log 10 Regulated by Kidney Metabolic component Increased Bicarbonate Increases the ratio Increases pH Metabolic Alkalosis AlkalOSIS Metabolic alkalosis :- Primary alkali ( biocarbonate ) excess 10/20/2014 12

13. Dr. Ashok Kumar J; IMS; MSU Metabolic acidosis 10/20/2014 13

14. Dr. Ashok Kumar J; IMS; MSU Loss of bicarbonate a. From gastrointestinal tract as in severe diarrhoea b. From the kidney as in Ureterosigmoidostomy Renal tubular acidosis is replaced by chloride Results in hyperchloremic acidosis 10/20/2014 14

15. Dr. Ashok Kumar J; IMS; MSU 10/20/2014 15

16. BUFFER SYSTEM Mainly bicarbonate buffer minimizes change in pH HCO 3 concentration is decreased and ratio of HCO 3 /H 2 CO 3 less than 20/1 RESPIRATORY MECHANISM Increases rate and depth of respiration ( Kussumauls breathing) Elimination of carbonic acid as CO 2 , Decrease in pCO 2 and consequently decrease in H 2 CO 3 Dr. Ashok Kumar J; IMS; MSU 10/20/2014 16

17. Dr. Ashok Kumar J; IMS; MSU RENAL compensation seta in 2 to 4 days Increases excretion of acid and preserves the base by increased rate of Na- H exchange Increases ammonia formation and increased reabsorption of HCO 3 10/20/2014 17

18. Dr. Ashok Kumar J; IMS; MSU Uncompensated Metabolic acidosis Partially compensated Metabolic acidosis Compensated Metabolic acidosis Fully compensated Partially compensated uncompensated Normal decreased decreased pH Decreased decreased normal pCO 2 Decreased decreased decreased HCO 3 pO 2 10/20/2014 18

19. Dr. Ashok Kumar J; IMS; MSU Metabolic alkalosis Raise in the plasma bicarbonate Loss of H+ ions Causes : Loss of gastric juice along with H+ ions as in - prolonged vomiting, - Nasogastric succion etc Therapeutic administration of large dose of alkali – chronic intake of excess antacids - Intravenous administration of bicarbonateetc 10/20/2014 19

20. Dr. Ashok Kumar J; IMS; MSU RESPIRATORY MECHANISM: Increase in pH depresses the respiratory center, causes retention of CO 2 pCO 2 which in turn increases the H 2 CO 3 . RENAL MECHANISM : Kidney decreases H + excretion decreased reclamation of bicarbonate. Compensatory mechanism 10/20/2014 20

21. Fully compensated Partially compensated uncompensated normal increased increased pH increased increased normal pCO 2 increased increased increased HCO 3 pO 2 Dr. Ashok Kumar J; IMS; MSU 10/20/2014 21

22. Thank you Dr. Ashok Kumar J; IMS; MSU 10/20/2014 22