Renal Regulation of Acid Base

Question 1

• Why must the [H+] of body fluids be kept constant?

Answer 1

So that detrimental changes in proteins, enzyme structure and cellular structure don’t occur

Question 2

• What is a buffer?

Answer 2

A buffer is a compound that can accept or donate protons and minimize the change in pH

Question 3

• What is the primary buffer of the ECF?

Answer 3

Bicarbonate

Question 4

• How is H+ excreted by the kidneys?

Answer 4

H+ cannot be excreted freely, therefore it is bound to filtered buffers such as phosphate or ammonia

Question 5

ammonia

• Which organs are involved in the bodies’ regulation of acid base balance?

Answer 5

Lungs, liver and kidneys

Question 6

• What are the two main roles of the proximal convoluted tubule?

Answer 6

Acidification & bicarbonate reabsorption

Question 7

• What enzyme catalyses the formation of H+ and HCO3-?

Answer 7

Carbonic anhydrase

Question 8

• What are the two mechanisms by which H+ leaves the proximal tubule cell and enters the PCT?

Answer 8

Via a Na+/H+ antiporter, via a H+/ATPase (proton pump)

Question 9

• What are the four major factors which control bicarbonate reabsorption?

Answer 9

Luminal HCO3- concentration, luminal flow rate, arterial pCO2, angiotensin II

Question 10

• What is the effect of parathyroid hormone?

Answer 10

An increase in hormone level increases cAMP and decreases bicarbonate reabsorption

Question 11

• What does secretion of H+ in cortical and medullary collecting tubules minimise?

Answer 11

K+ loss

Question 12

• Where is ammonium produced and why?

Answer 12

Ammonium is produced predominantly within the proximal tubular cells, the kidneys have the ability to excrete H+ as ammonium

Question 13

• How is ammonium produced? And what is one of the key by-products?

Answer 13

Produced from glutamine by the action of the enzyme glutaminase, bicarbonate is generated as a by-product

Question 14

• Which part of the renal tubules is involved in removing ammonium?

Answer 14

Thick ascending limb of the loop of Henle

Question 15

• What does a low pH augment?

Answer 15

Transfer of ammonium from the medullary interstitium into the luminal fluid as it passes through the medulla – increased ammonium excretion tends to increase extracellular pH towards normal

Question 16

• What does hypokalaemia cause?

Answer 16

Stimulates an increase in H+ secretion and HCO3- reabsorption