L30: Blood Gases, Acids And Bases

Question 1

Body constant acid production

Answer 1

1. CO2 (constant metabolism)
2. Non-volatile acid:
   - Lactate (from incomplete carbohydrates and fat metabolism)
   - Acetoacetate
   - Sulphuric acid (from protein metabolism)

Question 2

3 defence of body pH

Answer 2

1. Respiratory system
2. Kidney
3. Chemical buffers
   - HCO3
   - protein
   - phosphate

Question 3

Henderson-Hasselbach equation for HCO3 buffer system

Answer 3

pH = pKa + log [A-]/[HA]

—> pH = pKa + log [HCO3-]/[H2CO3]

—> pH = pKa + log [HCO3-]/k(PCO2)(k = solubility coefficient of CO2)

***Any defect in [HCO3-] —> Metabolic acidosis/alkalosis
Any defect in PCO2 —> Respiratory acidosis/alkalosis

Question 4

How body deals with increase in non-volatile acid and volatile acid

Answer 4

Non-volatile acid:
H+ (from non-volatile acid) + HCO3- —> H2O + CO2 (then excreted)

Volatile acid:
CO2 (from volatile acid) + H2O —> H+ + HCO3-

ALL catalysed by carbonic anhydrase

Question 5

CO2 release from tissue —> RBC —> lungs

Answer 5

In tissue:

1. CO2 diffuses into RBC (low O2 favours loading of CO2: Haldane effect)
2. CO2 + H2O —> H+ + HCO3- (carbonic anhydrase)
3. HCO3- moved out by chloride shift in
   * **4. H+ taken up by Hb and phosphate (H+ uptake helps Hb release O2 into tissue (HbO2- + H+ —> HHb + O2) —> Bohr’s effect)

In lungs:

1. HCO3- transported in blood
2. O2 + HHb —> HbO2- + H+ (Low CO2 favours loading of O2 (Bohr’s effect))
3. H+ + HCO3- —> H2O + CO2 in lungs (carbonic anhydrase)
4. CO2 is expired (High O2 favours unloading of CO2 (Haldane effect))

Question 6

Hb roles on release of CO2 and O2

Answer 6

In tissue: Hb bind H+ (from CO2) —> release O2

In lungs: Hb bind O2 —> release H+ —> + HCO3- —> release CO2

Question 7

Effect of ventilation rate on pH balance

Answer 7

CO2 + H2O ⇌ H2CO3 ⇌ HCO3- + H+

Adding CO2 (Hypoventilate) —> shift equilibrium to right —> lower pH

Removing CO2 (Hyperventilate) —> shift equilibrium to left —> increase pH