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Acids and Bases and Buffers

Acids Release H + into solution Bases Remove H + from solution Acids and bases Grouped as strong or weak. Buffers: Resist changes in pH When H + added, buffer removes When H + removed, buffer replaces Types of buffer systems Carbonic acid/bicarbonate Protein Phosphate.

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Acids and Bases and Buffers

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  1. Acids Release H+ into solution Bases Remove H+ from solution Acids and bases Grouped as strong or weak Buffers: Resist changes in pH When H+ added, buffer removes When H+ removed, buffer replaces Types of buffer systems Carbonic acid/bicarbonate Protein Phosphate Acids and Basesand Buffers

  2. Buffer Systems

  3. ACIDS AND BASES • Acid is a substance that can donate H+ ions and a base is a substance that can accept H+ ions . These properties are independent of charge. Thus, H2CO3, HCl, NH4+, and H2PO4- all can act as acids: •     H2CO3    <->    H+  +  HCO3- •          HCl   <->    H+  +  Cl- •       NH4+    <->    H+  +  NH3 •     H2PO4-   <->   H+  +  HPO42- •       Acid                Base

  4. General Acid-Base Relationships • Concentration of H+ ions in body: 40 Nano mol/lit • 40 / 1000,000,000 • 4 / 100,000,000 • 4 * 10-8 • Log 4*10-8 = (Log 4) - 8 • (0,6) – 8 = -7.4 • PH : - Log H+ concentration • PH : 7.4

  5. General Acid-Base RelationshipsLAW OF MASS ACTION The velocity of a reaction is proportional to the product of the concentrations of the reactants • Co2 + H2O Co3H2  Co3H- + H+ • H+ = (K)* Co3H- / Co3H2 • H+ = (k)* 24 / 40*0.03 • H+= (k)* 24/ 1.2 • H+= (k)* 20 • PH= Pk + Log 20 • PH= 6.1 + 1.3 • PH= 7.4

  6. General Acid-Base Relationships Henderson-Hasselbach equation: pH = pK + log HCO3_/pCO2 H+= 24 x pCO2/HCO3_ 0.1pH unit =10 nm/L H+

  7. Respiratory Regulation ofAcid-Base Balance • Respiratory regulation of pH is achieved through carbonic acid/bicarbonate buffer system • As carbon dioxide levels increase, pH decreases • As carbon dioxide levels decrease, pH increases • Carbon dioxide levels and pH affect respiratory centers • Hypoventilation increases blood carbon dioxide levels • Hyperventilation decreases blood carbon dioxide levels

  8. Respiratory Regulation ofAcid-Base Balance

  9. Renal Regulation of Acid-Base Balance • Secretion of H+ into filtrate and reabsorption of HCO3- into ECF cause extracellular pH to increase • HCO3- in filtrate reabsorbed • Rate of H+ secretion increases as body fluid pH decreases or as aldosterone levels increase • Secretion of H+ inhibited when urine pH falls below 4.5

  10. Kidney Regulation of Acid-Base Balance

  11. Hydrogen Ion Buffering

  12. Acidosis and Alkalosis • Acidosis: pH body fluids below 7.35 • Respiratory: Caused by inadequate ventilation • Metabolic: Results from all conditions other than respiratory that decrease pH • Alkalosis: pH body fluids above 7.45 • Respiratory: Caused by hyperventilation • Metabolic: Results from all conditions other than respiratory that increase pH • Compensatory mechanisms

  13. Regulation of Acid-Base Balance

  14. Regulation of Acid-Base Balance

  15. Acidosis and Alkalosis

  16. Vacoular H - ATPase (1) HCO3- Na 3 Na ATP 2 K+ HCO3- Na Na K+ CA II H+ + HCO3 H2O + CO2 + H+ Na H2O + CO2 3 HCO3 - HCO3 Net effect of Na/H+ , H - ATPase : Reabsorption Of 70% of bicarbonate

  17. Approach to Acid-Base Disorders • 1. Consider the clinical setting! • 2. Is the patient acidemic or alkalemic? • 3. Is the primary process metabolic or respiratory? • 4. If metabolic acidosis, gap or non-gap? • 5. Is compensation appropriate? • 6. Is more than one disorder present?

  18. Simple Acid-Base Disorders Primary Compensatory DisorderpHH+DisorderResponse Metabolic acidosis  HCO3_  pCO2 Metabolic alkalosis HCO3_  pCO2 Respiratory acidosis pCO2 HCO3_ Respiratory alkalosis pCO2 HCO3_

  19. Metabolic Acidosis • Etiology: Inability of the kidney to excrete the dietary H+ load, or increase in the generation of H+ (due to addition of H+ or loss of HCO3-)

  20. Metabolic Acidosis: Elevated Anion Gap AG = Na+ - (Cl- + HCO3-) = 12 ± 2 [Note: Diagnostic utility is best when AG > 25] Causes: Ketoacidosis Lactic acidosis Intoxications Renal failure Rhabdomyolysis

  21. Renal Tubular Acidosis Type 1 (distal)Type 2 (proximal) Type 4 Defect distal acid. prox HCO3 reab aldo HCO3 May be < 10 12-20 > 17 Urine pH > 5.3 Variable < 5.3 Plasma K Usually low Usually low High Response Good Poor Fair to HCO3 Rx

  22. Calculation of Bicarbonate Deficit • Bicarb deficit = HCO3- space x HCO3- deficit/liter • HCO3- space = 0.4 x lean body wt (kg) • HCO3- deficit/liter = [desired HCO3-] - [measured HCO3-]

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