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Lecture 21
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Lecture 21


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  • 1. POTASSIUM (K+)
    Dominant Intracellular Electrolyte
    Normal level of plasma in extracellular fluids is 3.5-5.1 mEq/l
  • 2. Potassium Function
    Potassium is responsible for control intracellular fluid osmolarity
    Maintaining resting membrane potential, nerve impulse and muscle contraction
    Play role in acid/base balance
  • 3. Potassium
    K is filtered through glomerulus
    K is reabsorbed to plasma at proximal convoluted tubule (PCT) and the loop of Henle
    Aldosterone reabsorb Na in the plasma and secret K in the distal convoluted tubule (DCT)
    Mostly K excreted in the urine
  • 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
    Hyperkalemia A high level of K in the extracellular fluid of more than 5.1 mEq/l may cause diarrhea, restlessness, muscle weakness
  • 5. Calcium
    Total Ca level in the plasma 9 – 11 mEq/l
    Hypercalcemia: Excess of Ca in the extracellular fluid fatigue, confusion, coma,
    Hypocalcemia: A low concentration of Ca in the extracellular fluids of less than 9 mEq/l muscle spasm occur
  • 6. Effect of calcitonin
    When Ca concentration too high. Thyroid gland releases calcitonin in the blood
    Calcitonin stimulate osteoblast which caused bone formation
    Calcitonin reduces Ca concentration
  • 7. Effect of parathyroid hormone
    When Ca concentration too low parathyroid gland releases parathyroid hormone
    PTH increases the activity of osteoclast which increases the Ca concentration in the plasma
    Parathyroid hormone increase the uptake of Ca from the filtrate in the kidney into the plasma
  • 8. Acid/Base Balance
    Homeostasis of hydrogen ion content
    Body fluids are classified as either acids or bases depending on H ion concentration
    Acid is an H donor and elevates the hydrogen ion content of the solution to which it is added
    Base is an H acceptor and can bind hydrogen ions
    Measure the acidity and alkalinity of a solution in units of pH, which is the measurement of free H ion in solution
    Normal pH of blood is 7.35-7.45 (alkaline)
  • 9. Acids
    During the process of cellular metabolism acids are continually being formed and excess hydrogen ions must be eliminated
    There are two types of acids formed: volatile acids are excreted by the lungs and nonvolatile acids are excreted by the kidney
    Volatile acids can be excreted from the body as gas. Carbonic acid produced by the hydration of carbon dioxide is a volatile acid
    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
  • 10.
  • 11.
  • 12. Some electrolyte found in the plasma:
    Basis: HCO3, HPO4, SO4
    Acid: H2CO3, H2PO4
  • 13. Regulation of pH
    Three methods control pH
    1. chemical buffers-when Hydrogen is removed a buffer replaces it
    2. regulation of carbon dioxide by respiratory system
    3. regulation of plasma bicarbonate concentration by the kidneys-slower, second line of defense
  • 14. Chemical buffers
    These are the first line of defense against changes in pH
    Act within a fraction of a second for immediate defense against H+ shift
    Buffers are composed of weak acid and weak base pairs
    Convert strong acids into weak acids and strong bases into weak bases
  • 15. Chemical Buffer System
    H2CO3/HCO3 buffer system
    H2PO4/HPO4 buffer system
    Proteins buffer
  • 16. Chemical Buffers
    Carbonic acid-bicarbonate system is most important extracellular buffer because it can be regulated by both lungs and kidneys
    Carbonic acid/bicarbonate ratio is usually 1:20
    Phosphates act as a buffer like the bicarbonate system does and protein buffers are the most abundant buffers in body cells and blood
  • 17. Regulation of pH through respiratory system
    Decreases respiration rate causes
    Increase CO2 in the plasma
    Less CO2 is exhaled
    Results in hypoventilation
    Accumulate CO2 results in increase H2CO3 and H concentration
    pH decreases
  • 18. Renal control of pH
    If acid increases kidney regulate pH by:
    Re-absorption of bicarbonate in proximal convoluted tubule
    Generate bicarbonate in the renal tubule
    Secreting H ions. In urine, hydrogen ion is buffered by phosphate and ammonia
    If the pH is high, bicarbonate is not re-absorbed in the renal tubule and eliminated
    pH decreases