Flashcards in Session 6 - Acidosis and Alkalosis Deck (79)
How do the kidneys control plasma volume?
• Filtering and variably recovering salts
How do the kidneys control plasma osmolarity?
• Filtering and variably recovering water
How do the kidneys variably control plasma pH?
• Filtering and variably recovering hydrogen carbonate and active secretion of hydrogen ions
What is normal pH range?
• 7.38 - 7.42
When does alkalaemia occur?
When does acidaemia occur?
What is normal conc of H+?
Outline what occurs in alkalaemia
• Lowers solubility of Ca2+ salts, free Ca2+ binds to proteins. Results in hypocalcaemia
○ Increases excitability of nerves
What is % mortality at pH 7.55?
What is % mortality at pH 7.65?
Outline what occurs in acidaemia
• Hyperkalaemia (heart arrythmias and arrest)
• Affects many enzymes
○ Reduces cardiac and skeletal muscle contractility
○ Reduced glycolysis in many tissues
○ Reduced hepatic function
• Effects severe under 7.1
• Life threatening below pH 7.0
How much HCO3- is required for accurate pH maintenance?
• 20x as much HCO3- as there is CO2
• pH = pK + log (HCO3-/pCO2 x 0.23)
• Log 20 (20x higher) = 1.3
• pK - 6.1 + 1.3 = 7.4
What is CO2 determined by?
• Controlled by chemoreceptors
• Disturbed by respiratory disease
What is HCO3- conc determined by?
• Controlled by kidney
Disturbed by metabolic and renal disease
What is HCO3- largely created by?
• Red blood cells
What is respiratory acidaemia (acidosis)?
• Hypoventilation leads to hypercapnia
• Hypercapnia causes plasma pH to fall
• Less than 20x amount of HCO3-
• pH <7.35
What is respiratory alkalaemia (alkalosis)?
• Hyperventilation leads to hypocapnia
• Fall in pCO2 causes pH to rise
• More than 20x amount of HCO3- than CO2
What is normal pH?
7.38 - 7.42
What is normal HCO3-
• 22 - 29 mmol/l
What is normal pO2?
• 9.8 - 14.2 kPa
What is normal pCO2?
• 4.2 - 6.0 kPa
How is pH corrected in respiratory alkalosis/acidosis?
• Central chemoreceptors normally control pCO2 within tight limits
• Peripheral chemoreceptors enable changes in respiration driven by changes in plasma pH
• This is CORRECTION - Changing the factor at hand
How is pH compensated in respiratory acidosis/alkalosis
• changes in pCO2 compensated by changes in HCO3-
• Kidney control HCO3-
• Respiratory acidosis is compensated by kidneys increasing HCO3-
• Respiratory alkalosis is compensated by kidneys decreasing HCO3-
What is metabolic acidosis?
• Tissues produce acid (or acid in blood - amino acids)
• H+ reacts with HCO3-, leading to fall in pH
How is metabolic acidosis compensated (acidosis means alteration in buffer base!)?
• Compensated by changes in ventilation
○ Peripheral chemoreceptors increase ventilation
○ This lowers pCO2
Restores pH towards normal
What is metabolic alkalosis caused by?
• Plasma HCO3- rises (after vomiting for instance)
• Plasma pH rises
• Metabolic alkalosis
How is metabolic alkalosis compensated?
• Partially compensated by decreased ventilation
How are respiratory changes in pH changed? (use correct terminology)
• Compensated by kidney
• Corrected by breathing
How are metabolic changes in pH modified? (use correct terminology)
• Compensated by breathing (changing factor than other directly changes)
• Corrected by kidney