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potassium homeostasis and its renal handling

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potassium homeostasis and its renal handling

  1. 1. Addis Ababa UniversityCollege of Health ScienceDepartment of Medical Physiology<br />Presentation on Potassium Homeostasis and its Renal Handling<br />By Girmay F<br />10/8/2011<br />1<br />
  2. 2. presentation out line <br />1.Objectives <br />2. Introduction <br />3. Physiological roles of potassium <br />4. Potassium homeostasis<br /> 4.1 Hormonal control of K+ homeostasis<br /> 4.2 Miscellaneous factors<br />5.Renal handling of potassium<br /> 5.1 K+ secretion by the principal cells <br /> 5.2 regulation of K+ excretion <br />6. Clinical correlations<br /><ul><li> Hyperkalemia
  3. 3. Hypokalemia</li></ul>7. References <br />10/8/2011<br />2<br />Potassium homeostasis and its renal handling<br />
  4. 4. 1.Objectives <br />At the end of this presentation students will able to:-<br /> Mention the major physiological role of potassium.<br />Explain the main mechanisms of potassium homeostasis.<br />Elaborate renal handling of potassium.<br />Identify factors that affect potassium excretion.<br />List the homeostatic disturbance of potassium.<br />10/8/2011<br />Potassium homeostasis and its renal handling<br />3<br />
  5. 5. 2.Introduction <br />The total body stores are approximately 50 to 55 meq/kg.<br />The main intracellular cation.<br />98% located ICF,150 meq/L.<br />2% located ECF,4meq/L.<br />90% readily exchangeable<br />10% non exchangeable<br />Amount ingested = up to 100meq/d = 2.5 gm/d<br />92% urinary excretion<br />8% GIT excretion<br />10/8/2011<br />4<br />Potassium homeostasis and its renal handling<br />
  6. 6. Introduction ..cont’d<br />10/8/2011<br />5<br />Potassium homeostasis and its renal handling<br />
  7. 7. 3.Physiological roles of potassium <br />1.Roles of intracellular K+:<br />Cellular volume maintenance<br />Intracellular pH regulation<br />Cell enzyme function<br />DNA/protein synthesis<br />Cell growth<br />2.Roles of transcellular K+ ratio:<br /><ul><li>Resting cell membrane potential
  8. 8. Neuromuscular excitability
  9. 9. Cardiac pacemaker rhythmicity</li></ul>10/8/2011<br />6<br />Potassium homeostasis and its renal handling<br />
  10. 10. 4.Potassium homeostasis <br />1.Internal balance ( ICF and ECF K+ distribution)<br />2. External balance ( Renal excretion of K+)<br />1.Internal balance<br />Physiological and pathological conditions can influence this process.<br /><ul><li>Hormones like insulin , catecholamines ,aldosterone
  11. 11. Acid base imbalance
  12. 12. Changes in osmolarity
  13. 13. Exercise
  14. 14. Cell lysis</li></ul>10/8/2011<br />7<br />Potassium homeostasis and its renal handling<br />
  15. 15. 4.1 Hormonal control of K+ homeostasis<br />Insulin and beta 2agonsists shifts K+ to the cell, by increase the activity of Na+,K+-ATPase, the 1Na+-1K+-2Cl- symporter, and the Na+-Cl- symporter.<br />Aldosterone acting on uptake of K+ into cells and altering urinary K+ excretion.<br />Stimulation of α-adrenoceptors releases K+ from cells, especially in the liver.<br />insulin and epinephrine act within a few minutes, aldosterone requires about an hour to stimulate uptake of K+ into cells. <br />10/8/2011<br />8<br />Potassium homeostasis and its renal handling<br />
  16. 16. 10/8/2011<br />9<br />Potassium homeostasis and its renal handling<br />
  17. 17. 10<br />Hormonal control of K+ homeostasis<br />
  18. 18. 4.2 Miscellaneous factors …..<br />1.Acid base imbalance <br />Metabolic acidosis increases the plasma [K+].<br /> Metabolic alkalosis decreases the plasma [K+] .<br />2.Plasma osmolarity <br /><ul><li>Hyperosmolarity associated with hyperkalemia .
  19. 19. A fall in plasma osmolality has the opposite effect. </li></ul>3.Cell lysis<br /><ul><li>Crush injury,burns,tumor lysis syndrome, rhabdomyolysis associated with destruction of cells and release of K+ to ECF. </li></ul>4. Exercise<br /> vigorous exercise, plasma [K+] may increase by 2.0 mEq/L. <br />10/8/2011<br />11<br />Potassium homeostasis and its renal handling<br />
  20. 20. …………Cont’d<br />Physiological: Keep Plasma [K+] Constant<br /> Epinephrine<br /> Insulin<br /> Aldosterone<br />Pathophysiological: Displace Plasma [K+] from Normal<br /> Acid-base balance<br /> Plasma osmolality<br /> Cell lysis<br /> Exercise<br />Drugs That Induce Hyperkalemia<br /> Dietary K+ supplements<br /> ACE inhibitors<br /> K+-sparing diuretics<br /> Heparin<br />10/8/2011<br />12<br />Potassium homeostasis and its renal handling<br />
  21. 21. 5.Renal handling of potassium<br />The PCT reabsorbs about 67% of the filtered K+ under most conditions by K+-H+ exchanger and K+-Cl- symport.<br />20% of the filtered K+ is reabsorbed by the TALH.<br /> The distal tubule and collecting duct are able to reabsorb or secrete K+.<br />10/8/2011<br />Potassium homeostasis and its renal handling<br />13<br />
  22. 22. ……….cont’d<br />The rate of K+ reabsorption or secretion by the distal tubule and collecting duct depends on a variety of hormones and factors.<br />Most of the daily variations in potassium excretion is caused by changes in potassium secretion in the distal and cortical collecting tubules.<br />10/8/2011<br />Potassium homeostasis and its renal handling<br />14<br />
  23. 23. ……………cont’d<br />10/8/2011<br />Potassium homeostasis and its renal handling<br />15<br />
  24. 24. 5.1 K+ SECRETION BY PRINCIPAL CELLS<br />Secretion from blood into the tubule lumen is a two-step process:<br />1.uptake of K+ from blood across the basolateral membrane by Na+,K+-ATPase and <br />2. diffusion of K+ from the cell into tubular fluid via K+ channels. <br /><ul><li>Three major factors that control the rate of K+ secretion by the distal tubule and the collecting duct </li></ul>The activity of Na+,K+-ATPase .<br />The driving force (electrochemical gradient) for movement of K+ across the apical membrane. <br />The permeability of the apical membrane to K+ .<br />10/8/2011<br />Potassium homeostasis and its renal handling<br />16<br />
  25. 25. ……..cont’d<br />10/8/2011<br />Potassium homeostasis and its renal handling<br />17<br />
  26. 26. ………….Cont’d<br />Intercalated cells reabsorb K+ via an H+,K+-ATPase transport mechanism located in the apical membrane . <br />This transporter mediates uptake of K+ in exchange for H+. This phenomena only occur during low potassium dietary intake.<br />10/8/2011<br />Potassium homeostasis and its renal handling<br />18<br />
  27. 27. 5.2 REGULATION OF K+ SECRETION ..<br />1.Dietary K+ <br />A diet high in K+ increases K+ secretion .a diet low in K+ decreases K+ secretions. <br />2. Aldosterone<br />Increases K+ secretion.<br />Hyperaldosteronism increases K+ secretion and causes hypokalemia .<br />Hypoaldestronism decreases K+ secretion and causes hyperkalemia <br />MOA<br />10/8/2011<br />Potassium homeostasis and its renal handling<br />19<br />
  28. 28. …………….cont’d<br />10/8/2011<br />Potassium homeostasis and its renal handling<br />20<br />
  29. 29. …..cont’d<br />3.Acid–Base <br />Acidosis decreases K+ secretion.<br />Alkalosis increases K+ secretion <br />Metabolic acidosis may either inhibit or stimulate excretion of K+ . <br />10/8/2011<br />Potassium homeostasis and its renal handling<br />21<br />
  30. 30. ………….cont’d<br />10/8/2011<br />Potassium homeostasis and its renal handling<br />22<br />
  31. 31. ………….Cont’d<br />4.Flow of Tubular Fluid <br />A rise in the flow of tubular fluid (e.g., with diuretic treatment, ECF volume expansion) stimulates secretion of K+ within minutes.<br />A fall (e.g., ECF volume contraction caused by hemorrhage, severe vomiting, or diarrhea) reduces secretion of K+ by the distal tubule and collecting duct. <br />MOA<br />10/8/2011<br />Potassium homeostasis and its renal handling<br />23<br />
  32. 32. ………….Cont’d<br />10/8/2011<br />Potassium homeostasis and its renal handling<br />24<br />
  33. 33. 10/8/2011<br />Potassium homeostasis and its renal handling<br />25<br />……………..Cont’d<br />
  34. 34. 6.Clinical correlations <br />10/8/2011<br />Potassium homeostasis and its renal handling<br />26<br />1.Hyperkalemia<br /> plasma concentration of K+ > 5.5 mEq / L<br />Causes <br /> a. Reduced excretion- acute renal failure <br /> -potassium –sparing diuretics.<br />b. Increased intake or release .<br /> -potassium supplements<br /> - Rhabdomyolysis <br /> -Hemolytic sates <br />
  35. 35. ………………..cont’d<br />c. Trans cellular shifts of potassium <br /><ul><li>Acidosis
  36. 36. Beta blockers ,cell destruction
  37. 37. Insulin deficiency
  38. 38. Addison’s disease
  39. 39. Cell lysis </li></ul>10/8/2011<br />Potassium homeostasis and its renal handling<br />27<br />
  40. 40. 28<br />……………….cont’d<br />Clinical manifestation <br />Early – hyperactive muscles , paresthesia<br />Late - Muscle weakness, flaccid paralysis<br />Dysrhythmias<br />Bradycardia , heart block, cardiac arrest<br />Change in ECG pattern<br /><ul><li>Appearance of tall, thin T waves on the ECG.
  41. 41. prolong the PR interval, depress the ST segment
  42. 42. Lengthen the QRS interval of the ECG.
  43. 43. As plasma [K+] approaches 10 mEq/L, the P wave disappears, the QRS interval broadens, the ECG appears as a sine wave, and the ventricles fibrillate .</li></li></ul><li>29<br />………..cont’d<br />2.Hypokalemia<br />Serum K+ < 3.5 mEq /L<br />Causes <br />In diabetic patient <br />Insulin gets K+ into cell<br />Ketoacidosis – H+ replaces K+, which is lost in urine<br />β – adrenergic drugs or epinephrine<br />
  44. 44. 30<br />……………cont’d<br />Decreased intake of K+<br />Increased K+ loss<br />Diuretics<br />Metabolic alkalosis <br />Trauma and stress<br />Conn’s diseases <br />Redistribution between ICF and ECF. <br />
  45. 45. 31<br />………….Cont’d<br />Clinical manifestation <br />Neuromuscular disorders<br />Weakness, flaccid paralysis, respiratory arrest, constipation<br />Dysrhythmias<br />Cardiac arrest <br />Prolongs the QT interval, inverts the T wave, and lowers the ST segment of the ECG. <br />
  46. 46. 7.References <br />Berne and levy physiology, sixth edition Bruce M.Koeppen, Bruce A. Stanton<br />Guyton and Hall Textbook of Medical Physiology, 12th Edition.<br />Human physiology: The Basis of Medicine, 3rd Edition.<br />Institutional websites <br />10/8/2011<br />Potassium homeostasis and its renal handling<br />32<br />
  47. 47. THANK YOU <br />

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