Friday, 2 January 2015

Fluid, Electrolyte and Acid-Base Balance III

pH: concentration of free hydrogen ions in a solution

Intracellular fluid has the lowest pH

Acidosis: When the pH of systemic arterial blood falls below the normal range
Alkalosis: When pH rises above the normal range

Respiratory acidosis: blood CO2 levels increase and blood pH drops due to low breathing rate
Metabolic acidosis: kidneys are unable to remove acid from the body; kidneys not functioning normally and is unable to remove H+ ions in urine

Respiratory alkalosis: blood CO2 levels drop and blood pH increases due to high breathing rate
Metabolic alkalosis: body lose large amounts of H+ (vommitting) or when large amounts of bicarbonate ions build up in body.




Ways to control pH
  1. Chemical buffer systems (fastest)
  2. Respiratory mechanisms
  3. Renal mechanisms (slowest)
Buffer systems

  1. Carbonic acid-bicarbonate buffer system
    • ALL BODY FLUID COMPARTMENTS
  2. Protein buffer system
    • blood plasma fluid and intracellular fluid
    • act as zwitterion
    • haemoglobin as a buffer (deoxyhaemoglobin)
  3. Phosphate buffer system
    • intracellular fluid



Respiratory mechanisms
- Can regulate the pH of the blood using rate and depth of breathing due to carbonic acid-bicarbonate buffer system

Alkalosis- respiratory muscles contract and relax more slowly, decreasing the rate of breathing
- Increased acidity of blood (less CO2 is exhaled, more H2CO3 produced, which dissociates, liberating more H+)

Acidosis- respiratory muscles contract and relax more rapidly, increasing rate and depth of breathing
- More Co2 exhaled, less H2CO3 produced, resulting in lower concentration of H+.



Renal compensation
  1. Na+/H+ antiporters
    • Increasing body pH by pumping H+ ions out of tubule epithelial cells and into the filtrate within the tubule lumen and then excreted as urine
  2. Reabsorption of bicarbonates
    • Reabsorbed from the glomerular filtrate in the proximal convoluted tubule of the nephron in the kidney
    • reabsorbed from intercalated cells at collecting ducts
  3. Regulation of urine pH
    • phosphate and ammonia




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