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Lec48

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Lec48

  1. 1. Regulation of acid base balance<br />Regulation of H+ concentration balance<br />Measuring the acidity and alkalinity of a solution in the units of pH, which is the measurement of the concentration of free H+ in solution <br />The H+ concentration of the body fluids normally is kept at a low level, which averages only 0.00004 mEq/L in the extracellular fluids<br />
  2. 2. Acids and bases definitions<br />Molecules containing hydrogen atoms that can release hydrogen ions in solutions are referred to as acids. HCl, which ionizes in water to form hydrogen ions (H+) and chloride ions Cl-<br />A base is an ion or a molecule that can accept an H+. For example, HCO3- is a base<br />
  3. 3. Alkalosis refers to excess removal of H+ from the body fluids<br />Acidosis refers to excess addition of H+<br />
  4. 4. Strong and Weak Acids and Bases<br />Strong acid: rapidly dissociates and releases especially large amounts of H+ in solution. An example is HCl <br />Weak acids have less tendency to dissociate their H+ ions in solution. An example is H2CO3<br />Strong base is one that reacts rapidly and strongly with H+ and, therefore, quickly removes these from a solution, (NaOH).<br />Weak base is HCO3- it binds with H+ much more weakly than does OH-. <br />Most of the acids and bases in the extracellular fluid that are involved in normal acid-base regulation are weak acids and bases. The most important ones are H2CO3 and bicarbonate base. <br />
  5. 5. pH is inversely related to the H+ concentration<br /> Low pH corresponds to a high H+ concentration, and a high pH corresponds to a low H+ concentration.<br />
  6. 6. Normal pH of arterial blood is 7.4, a person is considered to have acidosis when the pH falls below 7.4 and to have alkalosis when the pH rises above 7.4<br />The lower limit of pH at which a person can live more than a few hours is about 6.8, and the upper limit is about 8.0<br />
  7. 7. pH and H+ concentration of body fluids<br />
  8. 8. Defenses against changes in hydrogen ion concentration<br />There are three primary systems that regulate the H+ concentration in the body fluids to prevent acidosis or alkalosis: <br />(1) the chemical acid-base buffer systems of the body fluids<br />(2) the respiratory center<br />(3) the kidneys, which can excrete either acid or alkaline urine, thereby readjusting the extracellular fluid H+ concentration toward normal during acidosis or alkalosis<br />
  9. 9. Buffer system<br /> A chemical substance that minimizes changes in pH by releasing or binding hydrogen ions<br />
  10. 10. Buffer system<br />Most buffers composed of weak acid and weak base<br />The purpose of the buffer is to help the body maintain pH<br />Three important buffer system:<br />H2CO3/HCO3 buffer system<br />H2PO4-/HPO4-2 buffer system<br />Protein buffers<br />
  11. 11. Respiratory control of pH<br />Within body fluids, CO2 and H2O coming together to form H2CO2 which breaks down into HCO3- and H+<br />HCO3- and H+ are constantly forming H2CO3 which can split apart to form CO2 and H2O<br />
  12. 12. Respiratory control of pH<br />When we breathe more quickly, more CO2 leaves the body<br />When we breathe more slowly, less CO2 leaves the body<br />
  13. 13. Renal control of pH<br />The kidneys control acid-base balance by excreting either an acidic or a basic urine<br />Excreting an acidic urine reduces the amount of acid in the extracellular fluids<br />Excreting a basic urine removes base from the extracellular fluids<br />
  14. 14. Under normal conditions, almost all HCO3- are reabsorbed from the tubules, thereby conserving the buffer system of the extracellular fluid<br />This reabsorption of HCO3- are accomplished through the process of H+ secretion by the tubules<br />
  15. 15. Renal control of acid base balance<br />The kidneys regulate extracellular fluid H+ concentration through three mechanisms:<br />Secretion of H+<br />Reabsorption of filtered HCO3-<br />Production of new HCO3-<br />
  16. 16. About 80 to 90 per cent of the bicarbonate reabsorption (and H+ secretion) occurs in the proximal tubule<br />In the thick ascending loop of Henle, another 10 per cent of the filtered bicarbonate is reabsorbed<br />The remainder of the reabsorption takes place in the distal tubule and collecting duct<br />
  17. 17. Secretion of Hydrogen Ions <br />CO2 arrive at the kidney tubules cells <br />Within tubular cells, CO2 combine with H2O to form H2CO3 by carbonic anahydrase <br />Then H2CO3 split to HCO3 and H+<br />The H+ is secreted from the cell into the tubular lumen by Na-H counter transport<br />The HCO3- generated in the cell moves into the peritubular capillary blood<br />The epithelial cells in PCT, thick ascending limb and DCT all secrete H+ into the tubular lumen<br />
  18. 18. Reabsorption of HCO3- from filtrate<br />HCO3- that is filtered by the glomerulus combines with H+ to form H2CO3 which eventually becomes CO2 and H2O<br />The H2CO3 formed dissociate into CO2 and H2O <br />CO2 diffuses into tubular cell where it recombine with H2O under the influence of CA to generate H2CO3 <br />Then H2CO3 split to HCO3 and H+<br />The HCO3- generated in the cell moves into the renal interstitial fluid and the peritubular capillary blood<br />
  19. 19. Generating new HCO3-<br />H+ combined with HCO3- in the tubular fluid which results in reabsorption of HCO3-<br />If high H+ (as in acidosis), the kidneys generate new HCO3- by phosphate and ammonia buffers mechanisms<br />
  20. 20. Phosphate buffer system carries excess H+ into the urine and generate new bicarbonate<br />Phosphate buffer composed of HPO4= and H2PO4-<br />Excess H+ can combine with HPO4=<br />After H+ combines with HPO4= to form H2PO4 , it can be excreted as a NaH2PO4 carrying with it the excess H+ <br />
  21. 21. Excretion of excess H+ and generation of new HCO3- by ammonia buffer system<br />The glutamine delivered to the kidneys is transported into the epithelial cells of the proximal tubules, thick ascending loop of Henle, and distal tubules<br />Glutamine is metabolized to form two NH4+ and two HCO3-<br />The HCO3 is transported across the basolateral membrane along with reabsorbed Na+ into the peritubular capillaries<br />In chronic acidosis the dominant mechanism by which acid is eliminated is excretion of NH4+ <br />

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