5.8. Acid/Base Balance - Ammonium Excretion

Question 1

What is the purpose of ammonium excretion?

Answer 1

This is a major adaptive response to acid load

Question 2

What does ammonium secretion allow for?

Answer 2

1. Generation of new bicarbonate

2. Excretion of H+ ions

Question 3

1. Is NH3 lipid soluble?

2. Is NH4+ lipid soluble?

Answer 3

1. Yes

2. No

Question 4

What is the basis for the distal tubule mechanism of ammonium excretion?

Answer 4

1. NH3 being lipid soluble

2. NH4+ not being lipid soluble

Question 5

What is the process of ammonium excretion dependent on?

Answer 5

CO2 leaving the blood and entering into the Renal Tubule Cells

Question 6

What happens to the CO2, from the blood, which enters into the Renal Tubule Cells?

Answer 6

It combines with H2O to form Carbonic Acid (H2CO3)

Question 7

What happens to the newly formed Carbonic Acid?

Answer 7

It is in the presence of Carbonic Anhydrase, which causes the Carbonic acid to dissociate, forming H+ ions and Bicarbonate (HCO3-)

Question 8

What happens to the Bicarbonate formed within the Renal Tubule Cells?

Answer 8

It is excreted into the Peritubular Capillaries

Question 9

What happens to the H+ ions formed within the Renal Tubule Cells?

Answer 9

It is secreted into the Tubule Lumen

Question 10

1. What produces NH3?

2. Where does this occur?

Answer 10

1. Deamination of amino-acids (primarily glutamine) by the action of Renal Glutaminase
2. The Renal Tubule Cells

Question 11

What happens to the NH3, produced in the distal tubule cells?

Answer 11

It is excreted out into the tubule lumen

Question 12

What happens to the NH3, once it has been excreted into the tubule lumen?

Answer 12

It combines with the H+ ions, secreted from the Tubule Cells to form NH4+

Question 13

1. Where are NH4+/Na+ exchangers found?

2. What does this result in?

Answer 13

1. The proximal tubule

2. NH4+ being excreted into the lumen

Question 14

What happens to all of the NH4+ ions in the tubule lumen?

Answer 14

They react with Cl- ions, to form NH4Cl

Question 15

What happens to the NH4Cl?

Answer 15

It is excreted

Question 16

What is the activity of renal glutaminase (which produces NH3) dependent on?

Answer 16

pH - so when intracellular pH falls, there is an increase in renal glutaminase activity (therefore more NH4+ produced / excreted).

Question 17

1. Normally, how much H+ ions are lost as NH4+?

2. What can this rise to, in the case of severe acidosis?

Answer 17

1. 30-50mmols of H+ ions

2. 250mmol/L