Role of the Kidneys in Acid/Base Balance

Question 1

What is the molarity of [H+] at 7.40 pH?

Answer 1

0.00004 mmol/L

Question 2

What is the difference between acidosis and acidemia?

Answer 2

Acidemia is the state of having more protons in the blood, while acidosis is the process of getting more acid in the blood.

Question 3

How much metabolic acid is produced per day?

Answer 3

1 mmol/kg/day

Question 4

__________ acids must be eliminated by the kidneys.

Answer 4

Nonvolatile

Question 5

What two molecules often get metabolized to acidic compounds?

Answer 5

Nucleic acids (to phosphaturic acid) and sulfur-containing proteins

Question 6

How much nonvolatile acid does the average Westerner consume per day?

Answer 6

60 - 70 mmol

Question 7

List three general pH functions of the kidney.

Answer 7

Eliminate acid anions (sulfuric acid and phosphuric acid)
Reabsorb bicarb (~85% in the PCT)
Synthesize new bicarb (60 - 70 mmol daily; mainly in the intercalated cells of the DCT)

Question 8

Essentially no bicarb synthesis can take place until _____________.

Answer 8

bicarb reabsorption is complete

Question 9

How much HCO3 do we need to synthesize daily?

Answer 9

60 - 70 mmol

Question 10

Impaired proximal-tubule resorption of bicarb will result in ____________.

Answer 10

proximal renal tubule acidosis

Question 11

For every proton that is excreted, a new ________ is synthesized.

Answer 11

bicarb (this occurs because CO2 diffuses into the intercalated cells; carbonic anhydrase converts it to carbonic acid; a proton is excreted; and the remaining bicarb is reabsorbed)

Question 12

What prevents the urinary pH from being so low?

Answer 12

Titratable acids (creatinine, phosphate, and urate) and ammonia trapping keep the pH from being lower than 4.5

Question 13

NH3 diffuses easily through the _________.

Answer 13

apical membrane of the renal rubule

Question 14

NH3 binds to ______ and becomes trapped as ______.

Answer 14

H+; NH4+

Question 15

Ammonia is generated in the ___________ via ___________.

Answer 15

proximal tubule cells; glutaminase

Question 16

One molecule of bicarb can bind to _____ protons.

Answer 16

two

Question 17

Acidosis stimulates the bones to ______________.

Answer 17

release buffers such as phosphate and carbonate

Question 18

How is bicarb different than other buffers?

Answer 18

Other buffers just bind H+ in the blood. Bicarb carries it into the tubule and to excretion.

Question 19

With chronic metabolic alkalosis, bicarb excretion can go to _________.

Answer 19

80 mmol per day (from the usual zero)

Question 20

How does hypokalemia lead to metabolic alkalosis?

Answer 20

Hypokalemia induces the intercalated cells to preferentially reabsorb K and secrete H+. More H+ secretion happens alongside bicarb synthesis.

Question 21

Hyperkalemia induces metabolic acidosis, but hyperkalemia also ____________, a counteractive effect.

Answer 21

induces increased bicarb synthesis

Question 22

How is bicarb absorbed in the proximal tubule?

Answer 22

By conversion to CO2. Carbonic anhydrase converts HCO3 and a proton to CO2 and water. The CO2 diffuses into the PCT cells, where it is converted to HCO3 and a proton. The proton is pumped back into the lumen (to participate in the carbonic anhydrase reaction again) and the bicarb is actively pumped into the interstitium with sodium.

Question 23

There are two membrane transporters that are crucial for secreting acid and synthesizing bicarb in intercalated cells. What are they?

Answer 23

On the apical side, there are ATP proton pumps that secrete protons. On the basolateral side, there are bicarb/chloride antiporters that allow for the reabsorption of chloride.