Acid Base Balance In Fishes


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  • I suspect it should have been HPO42- as the stochiometery is off otherwise.
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  • Thank you very-very much for your work and your upload. It has been very enlightening. It was proposed by a good friend from US. I have a question to ask.
    On page 18 you write: H2PO42-
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Acid Base Balance In Fishes

  2. 2. Introduction <ul><li>Acid –base balance involves the maintenance of internal pH. </li></ul><ul><li>Regulation of acid –base homeostasis is of critical importance to fishes. </li></ul><ul><li>In order to achieve homeostasis, there must be a balance between the intake or production of hydrogen ions and the net removal of hydrogen ions from the body. </li></ul>
  3. 3. CONT…. <ul><li>A delicate balance of fluids, electrolytes, and acids and bases is required to maintain good health. </li></ul><ul><li>This balance is called Homeostasis </li></ul>
  4. 4. pH Review <ul><li>pH = - log [H + ] </li></ul><ul><li>H + is really a proton </li></ul><ul><li>Range is from 0 - 14 </li></ul><ul><li>If [H + ] is high, the solution is acidic; pH < 7 </li></ul><ul><li>If [H + ] is low, the solution is basic or alkaline ; pH > 7 </li></ul>
  5. 5. <ul><li>Acids are H + donors. </li></ul><ul><li>Bases are H + acceptors, or give up OH - in solution. </li></ul><ul><li>Acids and bases can be: </li></ul><ul><ul><li>Strong – dissociate completely in solution </li></ul></ul><ul><ul><ul><li>HCl, NaOH </li></ul></ul></ul><ul><ul><li>Weak – dissociate only partially in solution </li></ul></ul><ul><ul><ul><li>Lactic acid, carbonic acid </li></ul></ul></ul>
  6. 6. Body Fluids <ul><li>Intracellular fluid (ICF) </li></ul><ul><ul><li>found within the cells of the body </li></ul></ul><ul><ul><li>constitutes 2/3 of total body fluid </li></ul></ul><ul><ul><li>major cation is potassium </li></ul></ul><ul><li>Extracellular fluid (ECF) </li></ul><ul><ul><li>found outside the cells </li></ul></ul><ul><ul><li>accounts of 1/3 of total body fluid </li></ul></ul><ul><ul><li>major cation is sodium </li></ul></ul>
  7. 7. The Body and pH <ul><li>Homeostasis of pH is tightly controlled </li></ul><ul><li>Intracellular fluid = 7.2 – 7.5 </li></ul><ul><li>Blood pH = 7.7 – 8.0 </li></ul><ul><li>< 7.0 or > 8.5 death occurs </li></ul><ul><li>Acidosis (acidemia) below 7.4 </li></ul><ul><li>Alkalosis (alkalemia) above 8.3 </li></ul>
  8. 8. pH of Fish Blood 7.7 8.0 Normal blood pH Alkalosis Acidosis 8.2 8.4 7.4 7.2 7.0
  9. 9. Small changes in pH can produce major disturbances <ul><li>Most enzymes function only with narrow pH ranges </li></ul><ul><li>Acid-base balance can also affect electrolytes (Na + , K + , Cl - ) </li></ul><ul><li>Can also affect hormones </li></ul>
  10. 10. The body produces more acids than bases <ul><li>Acids take in with foods </li></ul><ul><li>Acids produced by metabolism of lipids and proteins </li></ul><ul><li>Cellular metabolism produces CO 2 . </li></ul><ul><li>CO 2 + H 2 0 ↔ H 2 CO 3 ↔ H + + HCO 3 - </li></ul>
  11. 11. How the Body defends against fluctuations in pH <ul><li>Three Systems in the body: </li></ul><ul><li>1.Buffers in the blood </li></ul><ul><li>2.Respiration through the gills </li></ul><ul><li>3.Excretion by the kidneys </li></ul>
  12. 12. Buffers in the Blood <ul><li>Buffers are substances that neutralize acids or bases </li></ul><ul><li>Bicarbonate which is a base and carbonic acid in the body fluids protect the body against changes in acidity </li></ul><ul><li>These buffer systems serve as a first line of defense against changes in the acid-base balance </li></ul>
  13. 13. Respiration through the gills <ul><li>Carbon Dioxide which is formed during cellular metabolism forms carbonic acid in the blood decreasing the pH </li></ul><ul><li>When the pH drops respiration rate increases this hyperventilation increases the amount of CO2 exhaled thereby lowering the carbonic acid concentration and restoring homeostasis </li></ul>
  14. 14. Excretion by the Kidneys <ul><li>The kidneys play the primary role in maintaining long term control of Acid-Base balance </li></ul><ul><li>The kidney does this by selecting which ions to retain and which to excrete </li></ul><ul><li>The kidneys adjust the body’s Acid-Base balance </li></ul>
  15. 15. Control of Acids <ul><li>Buffer systems: </li></ul><ul><ul><li>Take up H+ or release H+ as conditions change </li></ul></ul><ul><ul><li>Buffer pairs – weak acid and a base </li></ul></ul><ul><ul><li>Results in a much smaller pH change </li></ul></ul>
  16. 16. Cont… <ul><li>1. Extracellular buffer </li></ul><ul><li>- Bicarbonate , Ammonia </li></ul><ul><li>2.Intracellular buffer </li></ul><ul><li>- Protein, Phosphate </li></ul>
  17. 17. Bicarbonate buffer <ul><li>Sodium Bicarbonate (NaHCO 3 ) and carbonic acid (H 2 CO 3 ) </li></ul><ul><li>Maintain a 20:1 ratio : HCO 3 - : H 2 CO 3 </li></ul><ul><li>HCl + NaHCO 3 ↔ H 2 CO 3 + NaCl </li></ul><ul><li>NaOH + H 2 CO 3 ↔ NaHCO 3 + H 2 O </li></ul>
  18. 18. Phosphate buffer <ul><li>Major intracellular buffer </li></ul><ul><li>H + + HPO 4 2- ↔ H 2 PO4 - </li></ul><ul><li>OH - + H 2 PO 4 - ↔ H 2 O + H 2 PO 4 2- </li></ul>
  19. 19. Protein Buffers <ul><li>Non-bicarbonate buffers (Nbbs) – plasma proteins and hemoglobin. </li></ul><ul><li>Includes hemoglobin, work in blood </li></ul><ul><li>Carboxyl group gives up H + </li></ul><ul><li>Amino Group accepts H + </li></ul>
  20. 20. 2. Respiratory mechanisms <ul><li>Exhalation of carbon dioxide </li></ul><ul><li>CO 2 solubility in water is 25 times higher than that of oxygen ,so CO 2 is easily lost to the envt. </li></ul><ul><li>CO 2 + H 2 0 ↔ H 2 CO 3 ↔ H + + HCO 3 - </li></ul><ul><li>Body pH can be adjusted by changing rate and depth of breathing. </li></ul>
  21. 21. 3. Kidney excretion <ul><li>Can eliminate large amounts of acid </li></ul><ul><li>Can also excrete base </li></ul><ul><li>Can conserve and produce bicarb ions </li></ul><ul><li>Most effective regulator of pH </li></ul><ul><li>If kidneys fail, pH balance fails </li></ul>
  22. 22. Rates of correction <ul><li>Buffers function almost instantaneously </li></ul><ul><li>Respiratory mechanisms take several minutes to hours </li></ul><ul><li>Renal mechanisms may take several hours to days </li></ul>
  23. 25. Acid-Base Imbalances <ul><li>pH< 7.4acidosis </li></ul><ul><li>pH > 8.3 alkalosis </li></ul><ul><li>The body response to acid-base imbalance is called compensation </li></ul><ul><li>Partial compensation if range is still outside norms. </li></ul>
  24. 26. Compensation <ul><li>If underlying problem is metabolic, hyperventilation or hypoventilation can help : respiratory compensation . </li></ul><ul><li>If problem is respiratory, renal mechanisms can bring about metabolic compensation. </li></ul>
  25. 27. 7–8.0
  26. 28. There are 4 Types of Acid-base Imbalances <ul><li>1.Respiratory Alkalosis </li></ul><ul><li>2.Respiratory Acidosis </li></ul><ul><li>3.Metabolic Alkalosis </li></ul><ul><li>4.Metabolic Acidosis </li></ul>
  27. 29. Respiratory Alkalosis <ul><li>Is a decrease in CO2, decrease in H+ (Hydrogen ions) and in increase in pH </li></ul><ul><li>This condition can be caused by continuous fish movement or anxiety reaction </li></ul><ul><li>The body compensates by the gills slowing the respiration rate and kidneys excreting more bicarbonate </li></ul>
  28. 30. Respiratory Acidosis <ul><li>Is an increase in CO2, an increase in H+ and a decrease in pH </li></ul><ul><li>This condition can be caused by , restrictive or obstructive gill diseases </li></ul><ul><li>The body compensates by the gills increasing respiration rate and the kidneys by conserving bicarbonate ions and increasing renal net acid excretions </li></ul>
  29. 31. Metabolic Alkalosis <ul><li>Is a decrease in CO2, a decrease in H+ and an increase in pH </li></ul><ul><li>This condition can be caused by , increased ingestion of alkali </li></ul><ul><li>The body compensates by the gills creating a slow respiration rate and the kidneys excreting more bicarbonate </li></ul>
  30. 32. Metabolic Acidosis <ul><li>Is an increase in CO2, and increase in H+ and a decrease in pH </li></ul><ul><li>This condition can be caused by alkaline loss, excess acid production or ingestion </li></ul><ul><li>The body compensates by the gills increasing respiration rate and the kidneys increasing renal net acid excretion </li></ul>
  31. 34. Conclusion <ul><li>Fishes are capable of regulating their internal pH using both internal buffering and transepithelial exchanges across the gills. </li></ul><ul><li>Though their Pco 2 and HCO 3 - are well below those found in mammals, they can tolerate a variety of acid-base challenges. </li></ul>
  32. 35. <ul><li>QUERIES ? </li></ul>