The document discusses the kidney's role in acid-base regulation through excretion of hydrogen ions, reclamation of bicarbonate ions, and excretion of titrable acid and ammonia. It also addresses metabolic acidosis and alkalosis, noting that metabolic acidosis occurs when there is a primary deficit of bicarbonate ions, while metabolic alkalosis occurs when there is a primary excess of bicarbonate ions. Compensation mechanisms including buffer systems, respiration, and renal mechanisms act to regulate pH levels in the case of acid-base imbalances.

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2. Kidney plays a major role in acid-base regulation
1. Excretion of H+
2. Reclamation the bicarbonate ions present in the
Dr. Ashok Kumar J; IMS; MSU
ultra-filtrate
3. Excretion of titrable acid
4. Excretion of ammonia
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3. Dr. Ashok Kumar J; IMS; MSU
Tubular cell
HCO -
3
HCO3
- H+ H+
-
H2O + CO2 H2CO3
Tubular
Lumen
Na+ Na+
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4. Tubular cell Tubular
HCO - 3
HCO3
-
Dr. Ashok Kumar J; IMS; MSU
-
H2O + CO2 H2CO3
+ -
Lumen
H+ H+ HCO3
-
H2CO3
CO2 CO2 + H2O
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5. -
HCO3
-
H2O + CO2 H2CO3
H+ H+
Dr. Ashok Kumar J; IMS; MSU
Na2HPO4
Titrable acid
-
NaH2PO4
-
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7. When there is an excess of acid production in the body, H+
are excreted in urine as titrable acid and ammonia
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8. Anion Gap
In Extracellular fluid
Sum of anions = Sum of cations - Electrical neutrality
Dr. Ashok Kumar J; IMS; MSU
•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
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9. • Unmeasured anions constitute the anion gap
• Calculated as difference between measured cations and measured anions
Anion Gap = (Na+ + K+) - (Cl- + HCO3
-)
Dr. Ashok Kumar J; IMS; MSU
• Normal is about 12 mEq/L
e.g:
= ( 140 + 4) – (103 + 25)
= 16
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10. Acidosis : Clinical state where acids accumulate or bases are lost
Alkaosis : Clinical state where accumulation of base or loss of acids
[Bicarbonate]
Dr. Ashok Kumar J; IMS; MSU
pH pKa log10
[Carbonic acid]
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11. [Bicarbonate]
[Carbonic acid]
pH pKa log10
Dr. Ashok Kumar J; IMS; MSU
Regulated by Kidney
Metabolic component
Decreased Bicarbonate
Decreases the ratio
Decreases pH
Metabolic acidosis :- Primary alkali (bicarbonate) deficit
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12. [Bicarbonate]
[Carbonic acid]
pH pKa log10
Dr. Ashok Kumar J; IMS; MSU
Regulated by Kidney
Metabolic component
Increased Bicarbonate
Increases the ratio
Increases pH
Metabolic alkalosis :- Primary alkali (biocarbonate) excess
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13. • Diabetic ketoacidosis ; Starvation ketoacidosis; Lactic acidosis ;
Salicylate intoxication
• Renal failure ; Renal tubular acidosis type II
• Severe diarrhoea ; Renal tubular acidosis type I;
Ureterosigmoidostomy
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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
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16. BUFFER SYSTEM
 Mainly bicarbonate buffer minimizes change in pH
 HCO3 concentration is decreased and ratio of HCO3/H2 CO3 less than 20/1
RESPIRATORY MECHANISM
 Increases rate and depth of respiration (Kussumauls breathing)
 Elimination of carbonic acid as CO2 ,
 Decrease in pCO2 and consequently decrease in H2CO3
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17. RENAL compensation seta in 2 to 4 days
Increases excretion of acid and preserves the base by increased rate of
Dr. Ashok Kumar J; IMS; MSU
Na- H exchange
 Increases ammonia formation and increased reabsorption of HCO3
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18. • Uncompensated Metabolic acidosis
• Partially compensated Metabolic acidosis
• Compensated Metabolic acidosis
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Fully
compensated
Partially
compensated
uncompensated
pH decreased decreased Normal
pCO2 normal decreased Decreased
HCO3 decreased decreased Decreased
pO2
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19. Metabolic alkalosis
•Therapeutic administration of large dose of alkali
– chronic intake of excess antacids
- Intravenous administration of bicarbonateetc
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20. RESPIRATORY MECHANISM:
Increase in pH depresses the respiratory center, causes retention of CO 2
pCO2which in turn increases the H 2CO 3 .
Dr. Ashok Kumar J; IMS; MSU
RENAL MECHANISM:
 Kidney decreases H+ excretion
 decreased reclamation of bicarbonate.
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21. Fully
compensated
Partially
compensated
uncompensated
pH increased increased normal
pCO2 normal increased increased
HCO3 increased increased increased
pO2
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22. Thank you
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