Physio Renal 6.
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Physio Renal 6.

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Medical college lectures: Ranal physiology 2nd year.

Medical college lectures: Ranal physiology 2nd year.

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    Physio Renal 6. Physio Renal 6. Presentation Transcript

    • Acid – Base Balance. Dr.Mohamad Shaikhani.
      • one of the most important renal functions, regulating the acid – base balance of the body to ensure neutral PH of the body (not acidic & not alkaline) by regulating the hydrogen ion & bicarbonate concen of the body,
      • Blood 7.4,interstitium 7.35, intracellular 7 at which level the metabolic functions of the body are operating optimally.
      • Normal Hydrogen ion concentration of the body (H+) = 10(-8) – 1.6 *10(-7) MEQ/L.
      • PH = -LogH+ = 7.4.
      • Increased PH= low H+ = Alkalosis.
      • Decreased PH =High H+ = Acidosis.
      • Acid is a proton H+ Donor. Alkaline is H+ Acceptor.
      • Hcl is strong acid ,H2CO3 Weak acid , NaOH strong base & Na2HPO4 Weak base.
    • Buffer systems of the Body:
      • Are defense of the body against changes in the H+ ion concentration of the body. Their functions is to prevent marked changes(increase or decrease) in the body PH when a strong base or strong acid is added to the circulation ,by forming much weaker acid or base.
      • They are of 3 types:
      • 1.Acid – base Buffer systems:
      • A. Bicarbonate buffer system
      • B. Phosphate buffer system.
      • C. Protein buffer system.
      • 2. Respiratory regulation. Acts within 1 – 12 minutes in acute situations & within 1 day in chronic situations.
      • 3.Renal regulation: The most powerful buffering system, it requires many hours to several days to act maximally.
      • PH = - Log H+ ……………………..(1).
    • 1.Acid – base Buffer systems:
      • Is a mixture of a weak acid & a weak base( carbonic acid H2CO3 – bicarbonate NaHCO3 mixture), it prevents marked change in the PH of the body when strong acid or strong base is added to the circulation by forming much weaker acid or base as:
      • HCL (Strong Acid) + NaHCO3 = H2CO3(Weaker acid) + Nacl ….(2).
      • NaOH(Strong base) + H2CO3 = NaHCO3( Weaker base) +H2O…(3).
      • H2CO3 = H + + HCO3- ………………………………………...(4).
      • H+*HCO3-/H2CO3 = K …………………………………….….(5).
      • H+*HCO3/CO2 = K …………………………………………(6).
      • K = 1/400 K-
      • H+ = K*CO2/HCO3 …………………………………………(7).
      • Log H+ = Log K + LogCO2/HCO3 ………………………………(8).
      • -Log H+ = - Log K + LogHCO3/CO2 ………………………….(9).
      • PH = PK + LogHCO3/CO2 …………………………………...(10).
      • PH of the solution = PH of the buffer +pHCO3/CO2…………(11).
      • PH = 6.1 +LogHCO3/CO2………..(12).
      • Equation 12 is called Henderson – Hasselbach equation.
      • PH = 6.1 + Log 1 (if HCO3 = CO2).
      • PH = 6.1 + ZERO = 6.1
      • HCO3 Changed by renal system & CO2 by respiratory system.
    • The Buffering power of the Bicarbonate buffer system depends on:
      • 1.The ratio of bicarbonate to carbonic acid:
      • It is greatest when the ratio is 1 i.e PH = PK ,But it is still active when the ratio is 8/1 or 1/8.
      • 2.Contribution of the renal & respiratory systems:
      • Normally the ratio of NaHCO3/H2CO3 = 20/1 with blood PH of 7.4 & PK of 6.1 ,so it is not maximally active ,but the contribution of renal system by regeneration & retention of NaHCO3 & the respiratory system by regulating CO2(H2CO3) in blood makes this bicarbonate –carbonic acid buffer system a very powerful buffer system.
    • B. Phosphate buffer system.
      • Is a mixture of Na2HPO4 & NaH2PO4
      • HCL +Na2HPO4 = NaH2PO4 + NaCL ……………(13).
      • NaOH + NaHPO4 = Na2HPO4 + H2O …………..(14).
      • The PK of this buffer system is 6.8 very near the 7.4 (normal blood PH) , so it is very effective buffer system, even more effective than bicarbonate BS ,But its concentration in the blood is 1/12 of the bicarbonate BS concentration ,so as end result is less effective than Bicarbonate BS ,
      • But it is more effective buffering system in the renal tubules & inside cells of the body for buffering the H+ ion secreted by the kidneys & inside cells ,as its concentration in the renal tubules & cells is high.
    • C.Protein Buffer system:
      • Is important in buffering inside cells as the concentration of protein inside cells is high. The proteins are dissociated into amino acids which are acidic radicals giving H+ .
      • Bicarbonate BS diffuse slowly to inside cells ,so the protein BS inside cells corrects any acid – base abnormalities until the Bicarbonate BS arrives & corrects the final abnormalities after several hours.
    • 2.Respiratory regulation of Acid – Base balance:
      • Respiratory buffering power is ½ of all other buffering systems. Alveolar ventilation causes reciprocal changes in the H+ ion concentration of the blood as H+ in the blood affects the respiratory center causing increase or decrease in the alveolar ventilation.
      • CO2 = 1/Alveolar ventilation .
      • Alveolar ventilation can increase 15 times.
      • Feed back control of H ion concentration of the blood by respiratory center:
      • The efficiency of respiratory system buffering power is 50 – 75% ,when the acid – base abnormality is outside the respiratory system ,when PH shifts from normal of 7.4 to 7 or to 7.8 ,the respiratory system works in 1- 12 minutes returning the PH to 7.2 – 7.3 ,but not to normal i.e 50 – 75% efficient.
      • .In Acidosis kidneys secrete excess H+ in urine , while in Alkalosis kidneys regenerate & reabsorb bicarbonate.
      • .Renal Hydrogen H+ ion & bicarbonate secretion is directly related to H+ & Bicarbonate concentration in blood & ECF i.e in acidosis there will be more H+ secretion than Bicarbonate & vice versa in Alkalosis.
      • .Normally slightly more acid is secreted than bicarbonate
      • .Kidneys are more powerful buffering system but they are slow as chemical buffers act within seconds, respiratory system within minutes & kidneys within hours to days.
      3.Renal control of H+ ion concentration & acid – base balance:
    • Renal tubular secretion of H+ ion: Proximal tubules. Distal tubule. 1.Occure in proximal tubule segments.   2.Contributes to 95% of H+ secreted by kidneys. 3.Concentrates H+ *4. 4.It is secondary active secretion. 5.It occurs in all proximal tubular cells.   1.Occure in distal tubule segments & pelvis.   2.Contributes to 5% of H+ secreted by kidneys. 3.Concentrates H+ *900. 4.It is primary active secretion. 5.It occurs in only intercalated or dark cells.
    • Renal tubTransport of Excess H+ ion in the urine with urinary buffers: .Urinary PH is 6(4.8 – 8),only 1% of H ion secreted in urine is free while 99% is secreted with the urinary buffering systems which include: 1.Amonia BS. 2.Phosphate BS.
    • 1.Amonia BS in the renal tubules: Amonia is formed from Gultamin by the enzyme glutaminase in the tubular cells ,the formed ammonia diffuses into the lumen to bind the excess H+ secreted into the tubular lumen to form NH4 which binds with CL coming from NaCL to form NH4CL.
    • 2.Phosphate BS in the renal tubules: It is an effective buffer system in the renal tubules as its concentration there is high &its PK 6.8 near to the normal blood PH of 7.4.
    • Causes of Acid – Base abnormalities: Acidosis.   Alkalosis.   Respiratory Metabolic Respiratory Metabolic 1.Hypoventilation causing CO2 accumulation. 2.Respiratory center damage. 3.Respiratory obstruction. 4.Pneumonia. 1.Diabetes Mellitus. 2.Renal failure. 3.Acid ingestion. 4.Alcoholic ketoacidosis. 5.Lactic acidosis. 1.Hyperventilation causing CO2 wash as in hysteria or high altitude. 1.Diuretics. 2.Alkali ingestion. 3.Pyeloric obstruction. 4.Hyperaldosteronism.  
    • Clinical features: Acidosis: CNS depression leading to drowsiness ,confusion & coma with deep sighing respiration called kausmal’s breath. Alkalosis: On the other hand causes hyper excitability of the CNS causing tetany ,carpopedal spasm ,numbness & convulsions. Treatment: Acidosis: Sodium Bicarbonate or lactate or gluconate IV slowly. Alkalosis: Oral NH4CL or lysine monoHCL. PH measurements; By Glass electrode PH meter of plasma with special care during pl