L6 - Acid Base Balance II Flashcards
What is the long term way to regulate acid-base balance?
Renal mechanisms
What are the 3 renal mechanisms to controlling acid-base balance?
HCO3 handling - 90% proximal tubule - 10% distal tubule Urine acidification Ammonia synthesis
Proximal cell model - HCO3 handling
Na influx and recycling of halogen ion across apical membrane
This allows the cell to absorb 90% of the filtered bicarbonate
How is base conserved?
Acidification of urine – 25%
Ammonia synthesis - 75%
How is urine acidified?
In tubular fluid…which is then excreted in urine
- Alkaline salt –> acid salt
- Alkaline phosphate –> acid phosphate
- Na2HPO4 –> NaH2PO4
- Other examples - uric acid and creatinine
How is ammonia synthesised?
NH3 + H+ –> NH+4
- Ammonia is permeable
- Ammonium is impermeable
NH3 formed by glutamine –> alpha keto-glutarate
How do the kidneys respond to acidosis?
Increase in H+ excretion
Normal HCO3- excretion (nearly 0)
Decrease in urine pH
Increase in change in plasma pH
How do the kidneys respond to alkalosis?
Decrease in H+ excretion
Increase in HCO3- excretion
Increase in urine pH
Decrease in change in plasma pH
What are respiratory disorders caused by?
Changes in CO2 levels
What are metabolic disoders caused by?
Changes in acid and base levels
What are the two different types of respiratory disorders?
Respiratory acidosis – low pH and high [HCO3]
Respiratory alkalosis – high pH and low [HCO3]
What are the two different types of metabolic disorders?
Metabolic acidosis – low pH and low [HCO3]
Metabolic alkalosis – high pH and high [HCO3]
What is respiratory acidosis?
CO2 elimination decreases
Caused by lung diseases – emphysema, chronic bronchitis
What is the renal compensation for respiratory acidosis?
Increase in H+ secretion
Increase in reabsorption of HCO-3
Rise in pH but further rise in HCO-3
What is respiratory alkalosis?
CO2 elimination increases
Caused by hyperventilation, fear, stress, pain
What is the renal compensation for respiratory alkalosis?
Decrease in H+ secretion
Decrease in reabsorption of HCO-3
Fall in pH but further fall in HCO-3
What is metabolic acidosis caused by?
Ingestion acid or loss of alkaline fluid
Diarrhoea, cholera, diabetic ketoacidosis
What is the respiratory compensation for metabolic acidosis?
Increase in respiratory rate
Decrease in arterial PCO2
Increase in pH and drop in PCO2
What is the renal compensation for metabolic acidosis?
Increase in H+ secretion
Increase in reabsorption of HCO3-
What is metabolic alkalosis caused by?
Ingestion of alkaline fluid or loss of acid
Vomiting
What is the respiratory compensation for metabolic alkalosis?
Decrease in respiratory rate
Increase in arterial PCO2
Decrease in pH and rise in PCO2
What happened if you have a mix or respiratory and metabolic disorders?
Both same type – pH additive – life threatening
Opposite types – pH subtractive – mild
What are the 4 examples of mixed disorders?
Alcoholics
Asthma
COPD patients treated with diuretics
Salicylate poisoning
How do alcoholics have a mixed disorder?
Met acidosis (breakdown) Met alkalosis (vomiting)
How do asthma patients have a mixed disorder?
Respiratory acidosis Lactic acidosis (due to lack O2 for aerobic respiration)
How do COPD patients treated with diuretics have a mixed disorder?
Respiratory acidosis Metabolic alkalosis (caused by the diuretics)
How is salicylate poisoning a mixed disorder?
Respiratory alkalosis (stimulated respiratory centre) Metabolic acidosis
