Role of kidneys in regulation of Acid Base.pptx

Role of kidneys in regulation of Acid Base balance.pptx
HCO3 reabsorption and Hydrogen ion secretion
Acidosis and alkalosis
Metabolic acidosis
metabolic alkalosis

1. Role of kidneys in regulation of Acid Base balance By Dr. Irtaza Rehman Author of the book “The Extraordinary Life”

2. Learning objectives To understand acid base balance by kidneys To understand the mechanism of HCO3 - reabsorption and H+ secretion To know about compensatory mechanisms in metabolic acidosis and alkalosis.

3. How the factors are increasing or decreasing H + secretion and HCO3 - reabsorption??

4. Acids and Bases Acids release H + ions Bases accepts H + ions

5. Examples HCl H + + Cl - H2CO3 H + + HCO3 - H2PO4 H + + HPO4 -

6. Normal H+ ion concentration 40 nEq /L

7. Formula of pH pH = log 1 / [H + ] pH = -log [H + ] pH = -log [0.00000004] pH = 7.4 DEATH!! IF <6.8 >8

8. What are Buffers?? P revent a change in pH when H+ ions are added to or removed from a solution. 1. Extracellular buffers: Major  HCO3 Minor  Phosphate H2PO4 − / HPO4 − 2 (most important as Urinary Buffer)

9. 2. Intracellular buffers a. Organic phosphates (e.g., AMP, ADP, ATP) b. Proteins (e.g., Hemoglobin) What are Buffers??

10. What are types of Acid produced?? 1. V olatile acid CO2 produced from the aerobic metabolism of cells.

11. 2. Nonvolatile acids sulfuric acid (a product of protein catabolism) phosphoric acid (a product of phospholipid catabolism ) In pathologies: Ketoacids , lactic acids, oxalic acid etc What are types of Acid produced??

12. How to prevent acidosis or alkalosis?? 3 Systems 1. Buffer system of body fluids (within seconds) 2. Respiratory center (within minute) 3. Kidneys (hours to days) Slowest but Powerful

13. Renal control of Acid Base balance Excreting H + ions (acidic urine) Excreting HCO3 - ions (Basic urine)

14. By 3 Physiological changes HCO3 - reabsorption H + secretion New HCO3 - production Renal control of Acid Base balance

15. Filtered HCO3 - reabsorption: Early PCT Renal control of Acid Base balance

16. Q. Can filtered HCO3- be reabsorbed directly? Ans. No WHY?? Because luminal membrane of tubular cells are impermeable to HCO3- . That’s why it is first produced in tubular cells than reabsorbed passively . Because the basolateral membrane of tubular cells are permeable.

17. How to regulate the reabsorption of filtered HCO3 - ?? 1. Filtered load: Increased F.L  Increased Reabsorption If plasma level above normal  Inc Excretion

18. 2. PCO2 Increased PCO2  Increased HCO3 - reabsorption *Renal compensation for respiratory acidosis Decreased PCO2  Decreased HCO3 - reabsorption *Renal compensation for respiratory alkalosis How to regulate the reabsorption of filtered HCO3 - ??

19. 3. ECF Volume ECF expansion  Decreased HCO3 - reabsorption ECF contraction  Increased HCO3 - reabsorption How to regulate the reabsorption of filtered HCO3 - ??

20. Angiotensin II stimulates Na + – H + exchange and thus increases HCO3 − reabsorption contraction alkalosis that occurs secondary to ECF volume contraction. How to regulate the reabsorption of filtered HCO3 - ??

21. How H + ions are excreted?? As titratable acid (H2PO4) and NH4 + H.w : Why H2PO4 is known as titratable acid??

22. How H + ions are excreted?? As titratable acid (H2PO4) This process results in net secretion of H+ and net reabsorption of newly synthesized HCO3 -

23. How H + ions are excreted?? As titratable acid (H2PO4) Depends upon amount of urinary buffer and the pK of the buffer.

24. How H + ions are excreted?? as NH4 +

25. How H + ions are excreted?? as NH4 + Collecting tubular depends on amount of NH3 synthesized by renal cells and the urine pH.

26. How H + ions are excreted?? as NH4 + Diffusion Trapping: Diffusion of NH3 into tubular lumen bcz Collecting ducts are permeable to NH3 Trapping of NH4 in tubular lumen bcz colllecting ducts are less permeable to NH4

27. How H + ions are excreted?? as NH4 + Chronic acidosis: Increased NH4 Excretion Increased H +  Increased Renal glutamine Metabolism  Inc NH4 and Inc HCO3 - Hyperkalemia inhibits NH3 synthesis, which produces a decrease in H+ excretion as NH4 +

28. Tubular cells – Type A intercalated cells PCT, Thick Asc . limb, Early DCT Late DCT, Collecting ducts H + secreted: 80-90% Least possible pH: 6.7 (less efficient) H + secreted: 5% Least possible pH: 4.5(more efficient) Aldosterone

29. Q. Is there any mechanism for H+ ion reabsorption? Ans. NO If there is decreased H+ ions in blood, kidneys can only decrease their excretion to conserve them

30. Acid–base disorders Metabolic acidosis Overproduction or ingestion of fixed acid loss of base (HCO3 -) D ecrease in arterial [HCO3 - ]  Primary disturbance Decreased HCO3 -  Decreased pH ( acidemia )

31. Metabolic acidosis: How to compensate?? Respiratory: Decreased pH  Hyperventilation ( Kussmaul breathing) Renal: increased excretion of the excess fixed H + as titratable acid and NH4 + Increased new HCO3 - reabsorption Acid–base disorders

32. Q. Why HCO3- filtration is decreased in acidosis? Ans. Bcz more HCO3- will be used up in buffering the excess H+ ions in the ECF. Leads to Increased H+ secretion, bcz of less need to bind with HCO3- as it is low in filtrate.

33. Metabolic alkalosis Loss of fixed H + or gain of base Increase in arterial [ HCO3 - ]  Primary disturbance Increased HCO3 −  increase in blood pH ( alkalemia ) Acid–base disorders

34. Metabolic alkalosis: How to compensate?? Respiratory: Hypoventilation  Inc. CO2 Renal: Increased HCO3 - excretion Acid–base disorders

35. Metabolic alkalosis “ If metabolic alkalosis is accompanied by ECF volume contraction (e.g., vomiting), the reabsorption of HCO3− increases (secondary to ECF volume contraction and activation of the renin–angiotensin– aldosterone system), worsening the metabolic alkalosis (contraction alkalosis ) ” Acid–base disorders

36. Jazakumullahu Khair ♥ (May ALLAH swt reward you with goodness)