18. Renal Control of Acid-Base Balance

Question 1

What is the fate of bicarbonate once it enters through the glomerulus?

Answer 1

About 85% is immediately reabsorbed in the PCT. 14% is reabsorbed in other parts. About 1% is excreted.

Question 2

How is bicarbonate reabsorbed?

Answer 2

It is converted to H2O and CO2 by carbonic anhydrase. H2O and CO2 are then brought inside the cells where carbonic anhydrase converts them back to bicarbonate.

Question 3

Describe phosphate buffering of secreted hydrogen ions.

Answer 3

Once carbonic anhydrase regenerates bicarbonate in tubular cells, an H+ is sent out into the lumen where it will be buffered with NaHPO4- to become NaH2PO4. This leaves bicarbonate in the HCO3- form as it returns to the blood.

Question 4

During what process is “new” bicarbonate generated?

Answer 4

During urinary acidification where secreted H+ is buffered by NH3 –> NH4+, phosphate, ect, for excretion while bicarbonate is reabsorbed.

Question 5

What is the difference between α and β in intercalated cells?

Answer 5

α: secretes H+, reabsorbs HCO3-

β: reabsorbs H+, secretes HCO3-

Question 6

What constitutes most of the net acid excretion?

Answer 6

1/3 is titratable acids, primarily phosphate

2/3 is ammonium (NH4+) through synthesis and secretion

Question 7

What are the requirements to be in renal tubular acidosis (RTA)?

Answer 7

Acidemia
Normal anion gap
Normal serum creatinine
No diarrhea

Question 8

What is the primary defect in RTA Type 1?

Answer 8

Impaired distal H+ secretion. Presents with hypokalemia. Severe acidosis.

Question 9

What is the primary defect in RTA Type 2?

Answer 9

Impaired proximal HCO3- reabsorption. Presents with hypokalemia. Moderate-severe acidosis.

Question 10

What is the primary defect in RTA Type 4?

Answer 10

Lack of aldosterone or failure of kidney to respond to it. Presents with hyperkalemia. Low NH3 in urine. Mild acidosis. Most common.