Acid-Base balance

Question 1

What are the two places in the nephron where the kidney regulates acid/base balance?

Answer 1

• Proximal tubule
• Collecting duct

Question 2

What are the two methods of excreting acid in the proximal tubule?

Answer 2

• Protons out, sodium and bicarb in
• Glutamine metabolism

Question 3

Proximal tubule, sodium exchanger

Answer 3

In basolateral membrane (into body):
- Sodium reabsorption is coupled with bicarb

In apical membrane (into lumen):
- Sodium into the cell, protons exchanged, secreted

!! There are two things pushing sodium into the cell: concentration gradient and electrical gradient

Question 4

What happens when protons accumulates in the lumen of the proximal tubule?

Answer 4

• Protons combined with bicarbonate in the filtrate, forming water and CO2
• CO2 is freely permeable so absorbed into body (if not, effervessent urine)

Question 5

Glutamine metabolism

Answer 5

• Glutamine breakdown yields NH4, containing protons
• NH4 is exchanged for sodium in the apical membrane, sodium enters cell

Question 6

What are the two types of cells in the collecting duct that regulate acid/base balance?

Answer 6

Type A and Type B cells

Question 7

A cell of collecting duct

Answer 7

• Causes excretion of protons
• H2O and CO2 form bicarb and H+
• Bicarb absorbed into body, exchanged for chloride into cell
• To excrete the acid, there is no sodium exchanger like in the PT (trying to modulate Na+ levels in collecting duct)
• So, use a proton pump using ATP to pump H+ into the lumen
• H+ pumping causes potassium reabsorption

Question 8

H+ excretion causes what change in body levels of potassium?

Answer 8

Increase

Question 9

B cells

Answer 9

• H2O and CO2 –> bicarb and H+
• Bicarb into lumen, exchanged for chloride into cell
• In basolateral membrane, active pumping of protons back into the body
• H+ exchanged for K+, which is lost in urine

Question 10

At a normal pH in the body, there is much more ___ than ___

Answer 10

Bicarb than acid (CO2 and carbonic acid)

Question 11

Is there a lot of carbonic acid in the blood? CO2?

Answer 11

Little carbonic acid, mostly CO2

Question 12

What can happen to bicarb if there is an excess of acid, and what allows for this

Answer 12

• If there’s an excess of acid, it can bind with bicarbonate
• This is because there’s a lot more bicarb in the body than acid

(This means it’s more difficult to add more acid if pH is too high. However, CO2 is constantly made, so readily available)