Lecture 3: Acid Base Flashcards
Why is tight pH regulation necessary?
- Proper enzyme structure and function
- Proton gradient between inner and outer mitochondrial membrane drives oxidative phosphorylation which produces ATP
What is the normal concentration of H in arterial blood?
35-45 nmol/L
What is the normal range for pH in the blood?
7.35-7.45
What is the normal concentration of bicarbonate in the blood?
21-28 mmol/L
What is the normal range for pCO2?
35-45 mm Hg
How is regulation of pH achieved?
- HCO₃ reabsorption
- H⁺ excretion
- CO₂ Expiration
- Buffer systems in blood
How does HCO₃ reabsorption work to regulate pH?
- HCO₃ is filtered at glomeruli and almost all is reabsorbed in the proximal tubules of the kidney
- Luminal surface of the renal tubular cells of the kidney is impermeable to HCO₃ so it must convert into carbon dioxide and water
- Carbon dioxide and water can now go into the renal tubular cells where it is converted back into HCO₃ and H
- HCO₃ crosses the basolateral surface and enters blood
- H returns to the renal tubular lumen in exchange for Na
Where does H+ excretion occur? How does H⁺ excretion work to regulate pH?
- H+ excretion occurs in the distal convoluted tubule and the collecting duct
- H combines with buffers HPO₄ and NH₃ to form H₂PO₄ and NH₄⁺
- HCO₃ is regenerated in this process
How does buffer systems in blood work to regulate pH?
Buffers bind to H as they are generated and limit the increase in H concentration
What is the major extracellular and intracellular buffer?
Extra: bicarbonate
Intra: hemoglobin
What is the Henderson-Hasselbalch equation?
pH = 6.1 + log(HCO3/0.03xpCO2)
What are the acids produced by the human body?
Carbonic, phosphoric, sulphuric, lactic, and ketoacids
What are the acid base patterns associated with metabolic acidosis?
Low pH
High H
Very low bicarbonate
What are the causes of metabolic acidosis?
- H formation ex. ketoacidosis, lactic acidosis
- Decreased H excretion ex. renal failure, renal tubular acidosis
- Loss of bicarbonate ex. renal tubular acidosis type 2, diarrhea
What are the acid base patterns associated with respiratory acidosis?
Low pH
High H
Normal (acute) or high bicarbonate (chronic)
What are the causes of respiratory acidosis?
- Decreased respiratory drive ex. brain tumour
- Neuromuscular disease ex. toxins
- Airway obstruction ex. asthma
- Pulmonary disease ex. severe pneumonia
What are the acid base patterns associated with metabolic alkalosis?
High pH
Low H
Very high bicarbonate
Increased pCO2 due to compensation
What are the causes of metabolic alkalosis?
- Volume depletion ex. vomiting, gastric suction
- Potassium depletion ex. inadequate intake, increased excretion
- Alkali ingestion/administration
What are the acid base patterns associated with respiratory alkalosis?
High pH
Low H
Decreased pCO2
HCO3 normal (acute) or low (chronic)
What are the causes of respiratory alkalosis?
Increased ventilation
1. Brain tumour/trauma
2. High altitude, anemia, lung disease
3. Drugs
4. Anxiety
What does the body do to compensate for an acid base imbalance if it was a metabolic disorder?
Compensate by lungs to either increase or decrease the ventilation rate; fast
What does the body do to compensate for an acid base imbalance if it was a respiratory disorder?
Compensate by kidneys to change the excretion or absorption of protons or bicarbonate; slow
How does respiratory compensation work?
When pH is low and there is an increase in the concentration of hydrogen ions, excess hydrogen ions are buffered to form carbonic acid which decreases the amount of carbonate in the body. Excess hydrogen ions stimulate the respiratory center to increase the respiration rate in order to remove carbon dioxide.
How to calculate the anion gap? What is the normal range?
Na - (Cl + HCO₃)
8-12 mmol/L
What are the causes of metabolic acidosis with a normal anion gap?
- Diarrhea
- Renal tubular acidosis (RTA)
Type 1 - defect in H secretion in distal tubules
Type 2 - defect in bicarbonate reabsorption in PT
Type 3 - both 1 and 2
Type 4 - aldosterone deficiency, defect in HCO3 regeneration due to lack of urine buffers
What are the causes of metabolic acidosis with an elevated anion gap?
G - Glycols
O - Oxaproline
L - L-lactate
D - D-lactate
M - Methanol
A - Aspirin
R - Renal failure
K - Ketoacidosis
What should you do when you solve an acid base problem?
- pH
- Respiratory or metabolic? (pCO2 and HCO3)
- Compensation and secondary disorders
- If metabolic acidosis, calculate anion gap
