Lecture 3: Acid Base

Question 1

Why is tight pH regulation necessary?

Answer 1

1. Proper enzyme structure and function
2. Proton gradient between inner and outer mitochondrial membrane drives oxidative phosphorylation which produces ATP

Question 2

What is the normal concentration of H in arterial blood?

Answer 2

35-45 nmol/L

Question 3

What is the normal range for pH in the blood?

Answer 3

7.35-7.45

Question 4

What is the normal concentration of bicarbonate in the blood?

Answer 4

21-28 mmol/L

Question 5

What is the normal range for pCO2?

Answer 5

35-45 mm Hg

Question 6

How is regulation of pH achieved?

Answer 6

1. HCO₃ reabsorption
2. H⁺ excretion
3. CO₂ Expiration
4. Buffer systems in blood

Question 7

How does HCO₃ reabsorption work to regulate pH?

Answer 7

1. HCO₃ is filtered at glomeruli and almost all is reabsorbed in the proximal tubules of the kidney
2. Luminal surface of the renal tubular cells of the kidney is impermeable to HCO₃ so it must convert into carbon dioxide and water
3. Carbon dioxide and water can now go into the renal tubular cells where it is converted back into HCO₃ and H
4. HCO₃ crosses the basolateral surface and enters blood
5. H returns to the renal tubular lumen in exchange for Na

Question 8

Where does H+ excretion occur? How does H⁺ excretion work to regulate pH?

Answer 8

1. H+ excretion occurs in the distal convoluted tubule and the collecting duct
2. H combines with buffers HPO₄ and NH₃ to form H₂PO₄ and NH₄⁺
3. HCO₃ is regenerated in this process

Question 9

How does buffer systems in blood work to regulate pH?

Answer 9

Buffers bind to H as they are generated and limit the increase in H concentration

Question 10

What is the major extracellular and intracellular buffer?

Answer 10

Extra: bicarbonate
Intra: hemoglobin

Question 11

What is the Henderson-Hasselbalch equation?

Answer 11

pH = 6.1 + log(HCO3/0.03xpCO2)

Question 12

What are the acids produced by the human body?

Answer 12

Carbonic, phosphoric, sulphuric, lactic, and ketoacids

Question 13

What are the acid base patterns associated with metabolic acidosis?

Answer 13

Low pH
High H
Very low bicarbonate

Question 14

What are the causes of metabolic acidosis?

Answer 14

1. H formation ex. ketoacidosis, lactic acidosis
2. Decreased H excretion ex. renal failure, renal tubular acidosis
3. Loss of bicarbonate ex. renal tubular acidosis type 2, diarrhea

Question 15

What are the acid base patterns associated with respiratory acidosis?

Answer 15

Low pH
High H
Normal (acute) or high bicarbonate (chronic)

Question 16

What are the causes of respiratory acidosis?

Answer 16

1. Decreased respiratory drive ex. brain tumour
2. Neuromuscular disease ex. toxins
3. Airway obstruction ex. asthma
4. Pulmonary disease ex. severe pneumonia

Question 17

What are the acid base patterns associated with metabolic alkalosis?

Answer 17

High pH
Low H
Very high bicarbonate
Increased pCO2 due to compensation

Question 18

What are the causes of metabolic alkalosis?

Answer 18

1. Volume depletion ex. vomiting, gastric suction
2. Potassium depletion ex. inadequate intake, increased excretion
3. Alkali ingestion/administration

Question 19

What are the acid base patterns associated with respiratory alkalosis?

Answer 19

High pH
Low H
Decreased pCO2
HCO3 normal (acute) or low (chronic)

Question 20

What are the causes of respiratory alkalosis?

Answer 20

Increased ventilation
1. Brain tumour/trauma
2. High altitude, anemia, lung disease
3. Drugs
4. Anxiety

Question 21

What does the body do to compensate for an acid base imbalance if it was a metabolic disorder?

Answer 21

Compensate by lungs to either increase or decrease the ventilation rate; fast

Question 22

What does the body do to compensate for an acid base imbalance if it was a respiratory disorder?

Answer 22

Compensate by kidneys to change the excretion or absorption of protons or bicarbonate; slow

Question 23

How does respiratory compensation work?

Answer 23

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.

Question 24

How to calculate the anion gap? What is the normal range?

Answer 24

Na - (Cl + HCO₃)
8-12 mmol/L

Question 25

What are the causes of metabolic acidosis with a normal anion gap?

Answer 25

1. Diarrhea 2. 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

Question 26

What are the causes of metabolic acidosis with an elevated anion gap?

Answer 26

G - Glycols O - Oxaproline L - L-lactate D - D-lactate M - Methanol A - Aspirin R - Renal failure K - Ketoacidosis

Question 27

What should you do when you solve an acid base problem?

Answer 27

1. pH 2. Respiratory or metabolic? (pCO2 and HCO3) 3. Compensation and secondary disorders 4. If metabolic acidosis, calculate anion gap