Chapter 2 Acid-Base/Potassium

Question 1

What percentage of filtered bicarbonate is resorbed in the proximal tubule?

Answer 1

80 - 85% of filtered bicarbonate is resorbed in the proximal tubule.

*Distal bicarbonate resorption is small but can increase in disorders of the proximal tubule.

Question 2

What transporter is used in acute metabolic acidosis?

Answer 2

The sodium-bicarbonate transporter NBC-1 is recruited into the basolateral membrane to enhance bicarbonate resorption in acute metabolic acidosis.

Question 3

What happens to NBC-1 in metabolic alkalosis?

Answer 3

The NBC-1 transporter is redistributed to the cytoplasm in metabolic alkalosis, thereby reducing bicarbonate resorption.

Question 4

What happens to NBC-1 in respiratory acidosis?

Answer 4

NBC-1 protein synthesis is unregulated in respiratory acidosis.

Question 5

Where does H+ secretion occur?

Answer 5

Secretion of hydrogen ions occurs predominantly in the late distal tubule, connecting segment and collecting tubules.

Question 6

What four factors are necessary for optimal secretion of hydrogen ions and potassium?

Answer 6

1. Adequate sodium delivery to the distal nephron
2. Presence of aldosterone
3. Intact ENaC
4. Good urine flow

Question 7

What is the substrate for ammoniagenesis?

Answer 7

Glutamine is the substrate for ammoniagenesis.

Question 8

What two factors stimulate ammoniagenesis?

Answer 8

1. Metabolic acidosis

2. Hypokalaemia

Question 9

What should lead you to suspect renal tubular acidosis?

Answer 9

1. Non-anion gap metabolic acidosis
2. Positive urine anion gap
3. Urine osmolality gap < 150 mEq/kg