ACID EXCRETION

Question 1

What are the two broad types of acid produced in the body? Which organ excretes each one?

Answer 1

Volatile (CO₂): lungs

Non-volatile: buffered in plasma by bicarbonate from kidneys

Question 2

Where does most of the HCO₃ reabsorption happen in the kidneys? Which channels are involved?

Answer 2

Proximal tubule (~80%)

​sodium/hydrogen pump + sodium/HCO₃ pump

Question 3

Where is HCO3 generated in the kidney?

Answer 3

Collecting duct

Carbon dioxide and water combine to form HCO₃ and hydrogen. HCO₃ reabsorbed and hydrogen excreted in urine

Question 4

Since bicarbonate is being reabsorbed through the kidney and not excreted, what is buffering the hydrogen ions that are being excreted in urine thus preventing the hydrogen from damaging their nephron?

Answer 4

Phosphate

Ammonia

Question 5

In an acidotic state an increase of which 2 buffers will be seen in the urine? How would you work out if this is happening?

Answer 5

Ammonium and phosphate (titratable acid)

24-hour urine collection. Work out net acid excretion by:

(titratable acid + ammonium) - HCO3

Positive value indicates acid is being excreted