Lecture 21


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Lecture 21

  1. 1. POTASSIUM (K+)<br />Dominant Intracellular Electrolyte<br />Normal level of plasma in extracellular fluids is 3.5-5.1 mEq/l<br />
  2. 2. Potassium Function<br />Potassium is responsible for control intracellular fluid osmolarity <br />Maintaining resting membrane potential, nerve impulse and muscle contraction<br />Play role in acid/base balance<br />
  3. 3. Potassium <br />K is filtered through glomerulus<br />K is reabsorbed to plasma at proximal convoluted tubule (PCT) and the loop of Henle<br />Aldosterone reabsorb Na in the plasma and secret K in the distal convoluted tubule (DCT)<br />Mostly K excreted in the urine <br />
  4. 4. Hypokalemia: A below level of K in the extracellular fluids of less than 3.5 mEq/l, may cause skeletal muscle weakness, respiratory arrest<br />Hyperkalemia A high level of K in the extracellular fluid of more than 5.1 mEq/l may cause diarrhea, restlessness, muscle weakness<br />
  5. 5. Calcium<br />Total Ca level in the plasma 9 – 11 mEq/l<br />Hypercalcemia: Excess of Ca in the extracellular fluid fatigue, confusion, coma, <br />Hypocalcemia: A low concentration of Ca in the extracellular fluids of less than 9 mEq/l muscle spasm occur <br />
  6. 6. Effect of calcitonin<br />When Ca concentration too high. Thyroid gland releases calcitonin in the blood<br />Calcitonin stimulate osteoblast which caused bone formation<br />Calcitonin reduces Ca concentration<br />
  7. 7. Effect of parathyroid hormone<br />When Ca concentration too low parathyroid gland releases parathyroid hormone <br />PTH increases the activity of osteoclast which increases the Ca concentration in the plasma <br />Parathyroid hormone increase the uptake of Ca from the filtrate in the kidney into the plasma <br />
  8. 8. Acid/Base Balance<br />Homeostasis of hydrogen ion content<br />Body fluids are classified as either acids or bases depending on H ion concentration<br />Acid is an H donor and elevates the hydrogen ion content of the solution to which it is added<br />Base is an H acceptor and can bind hydrogen ions<br />Measure the acidity and alkalinity of a solution in units of pH, which is the measurement of free H ion in solution<br />Normal pH of blood is 7.35-7.45 (alkaline)<br />
  9. 9. Acids<br />During the process of cellular metabolism acids are continually being formed and excess hydrogen ions must be eliminated <br />There are two types of acids formed: volatile acids are excreted by the lungs and nonvolatile acids are excreted by the kidney<br />Volatile acids can be excreted from the body as gas. Carbonic acid produced by the hydration of carbon dioxide is a volatile acid <br />Normally carbon dioxide is excreted by the lungs as fast as metabolism produces it, so carbonic acid is not allowed to accumulate and alter pH<br />
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  12. 12. Some electrolyte found in the plasma:<br />Basis: HCO3, HPO4, SO4<br />Acid: H2CO3, H2PO4 <br />
  13. 13. Regulation of pH<br />Three methods control pH<br />1. chemical buffers-when Hydrogen is removed a buffer replaces it<br />2. regulation of carbon dioxide by respiratory system<br />3. regulation of plasma bicarbonate concentration by the kidneys-slower, second line of defense<br />
  14. 14. Chemical buffers<br />These are the first line of defense against changes in pH<br />Act within a fraction of a second for immediate defense against H+ shift<br />Buffers are composed of weak acid and weak base pairs<br />Convert strong acids into weak acids and strong bases into weak bases<br />
  15. 15. Chemical Buffer System<br />H2CO3/HCO3 buffer system<br />H2PO4/HPO4 buffer system<br />Proteins buffer <br />
  16. 16. Chemical Buffers<br />Carbonic acid-bicarbonate system is most important extracellular buffer because it can be regulated by both lungs and kidneys<br />Carbonic acid/bicarbonate ratio is usually 1:20<br />Phosphates act as a buffer like the bicarbonate system does and protein buffers are the most abundant buffers in body cells and blood<br />
  17. 17. Regulation of pH through respiratory system<br />Decreases respiration rate causes <br />Increase CO2 in the plasma<br />Less CO2 is exhaled<br />Results in hypoventilation<br />Accumulate CO2 results in increase H2CO3 and H concentration <br />pH decreases<br />
  18. 18. Renal control of pH<br />If acid increases kidney regulate pH by:<br />Re-absorption of bicarbonate in proximal convoluted tubule<br />Generate bicarbonate in the renal tubule<br />Secreting H ions. In urine, hydrogen ion is buffered by phosphate and ammonia<br />If the pH is high, bicarbonate is not re-absorbed in the renal tubule and eliminated<br />pH decreases<br />