Role Of Kidneys

Question 1

What are the three fundamental mechanisms by which the kidneys control acid-base balance?

Answer 1

1. Secretion of H+
2. Reabsorption of filtered HCO3-
3. Production of new HCO3-

These mechanisms help maintain the pH of extracellular fluid.

Question 2

What is the pH range of acidic urine?

Answer 2

Lower than 5.0

Question 3

What is the pH range of basic urine?

Answer 3

8.0 to 8.5

Question 4

What happens if more H+ is secreted than HCO3- is filtered?

Answer 4

There will be a net loss of acid from the extracellular fluid.

Question 5

What occurs if more HCO3- is filtered than H+ is secreted?

Answer 5

There will be a net loss of base.

Question 6

In which parts of the renal tubules do hydrogen ion secretion and bicarbonate reabsorption occur?

Answer 6

Virtually all parts except the descending and ascending thin limbs of the loop of Henle.

Question 7

What is the role of the sodium-hydrogen exchanger protein in the kidneys?

Answer 7

It couples the active secretion of H+ with the transport of Na+ into the cell.

Question 8

What is the source of energy for H+ secretion against a concentration gradient?

Answer 8

The sodium gradient favoring Na+ movement into the cell.

Question 9

What enzyme facilitates the formation of H2CO3 from CO2 and H2O in the tubular cells?

Answer 9

Carbonic anhydrase

Question 10

What happens to H2CO3 after it is formed in the tubular cells?

Answer 10

It dissociates into CO2 and H2O.

Question 11

How is HCO3- transported across the basolateral membrane?

Answer 11

By Na+/HCO3- co-transport and Cl-/HCO3- exchange.

Question 12

What occurs during metabolic alkalosis regarding HCO3-?

Answer 12

Excess HCO3- cannot be reabsorbed and is excreted into the urine.

Question 13

What occurs during acidosis regarding HCO3- and H+?

Answer 13

Excess H+ passes into the urine while HCO3- is completely reabsorbed.

Question 14

What is the primary mechanism by which kidneys correct acidosis or alkalosis?

Answer 14

Incomplete titration of H+ against HCO3-.

Question 15

How is H+ secreted in the late distal tubule and collecting tubules?

Answer 15

By primary active transport via a hydrogen-transporting ATPase.

Question 16

What stimulates increased H+ secretion by the tubules in acidosis?

Answer 16

1. Increase in PCO2 of the extracellular fluid
2. Increase in H+ concentration of the extracellular fluid (decreased pH)

Question 17

What buffers are primarily used for H+ excretion in the urine?

Answer 17

1. Phosphate buffer
2. Ammonia buffer

Question 18

What happens when H+ combines with HPO42- in the tubular fluid?

Answer 18

It forms H2PO4-, which can be excreted as a sodium salt (NaH2PO4).

Question 19

What is formed from the metabolism of glutamine in the renal tubular cells?

Answer 19

2 NH4+ and 2 HCO3-

Question 20

How does extracellular fluid H+ concentration affect renal glutamine metabolism?

Answer 20

Increase in H+ concentration stimulates metabolism; decrease has the opposite effect.

Question 21

What is the role of ammonia buffer during acidosis?

Answer 21

Significantly increases during chronic acidosis but not during acute acidosis.