Keef: Renal handling of bicarbonate

Question 1

What do the kidneys do to help mitigate changes in acid load?

Answer 1

1) The kidneys conserve filtered bicarbonate
2) The kidneys can make “new” bicarbonate to replace the bicarbonate lost during buffering.
3) The kidneys can excrete excess bicarbonate (alkalosis)
4) The kidneys can excrete fixed acid
H2CO3 HCO3-(New) + H+(excrete

Question 2

In the proximal tubule, how low can the pH go?

Answer 2

6

Question 3

In the distal tubule, how low can the pH go?

Answer 3

4.4

Question 4

In the distal tubule, is there carbonic anhydrase in the membrane between the cell and the tubular lumen?

Answer 4

No!

Question 5

What else is different about bicarbonate absorption in the distal nephron?

Answer 5

The H+ cannot move freely into the tubular lumen via the exchange of Na+. Instead it must use an H+ATP-ase.

Question 6

What kind of cells are found in the distal nephron, which secrete H+?

Answer 6

alpha intercalated cells

Question 7

During alkalosis, what happens to excretion of bicarb?

Answer 7

It increases! If the pH goes up, less H+ secretion, so more bicarb will show up in the urine, because it is not being reabsorbed, and urine pH will become more basic.

Question 8

What is the main point of carbonic anhydrase inhibitors?

Answer 8

Increase bicarb excretion by blocking carbonic anhydrase. This returns pH toward 7.4

Question 9

2 methods in which the kidney can eliminate fixed acid?

Answer 9

1. Formation of NH4+ (NH4+ can be secreted in proximal tubule from glutamine–>NH4+ + HCO3-; in the distal nephron, it is secreted as NH3+ and combines with H+ to form NH4Cl)
2. Formation of titratable acid

Question 10

What is the predominate titratable acid in the tubular fluid?

Answer 10

Phosphate

Question 11

At low pH, what form is phosphate in?

At high pH?

Answer 11

H2PO4-

HPO42-

Question 12

Predominate form of phosphate in the body. What does it get converted to in the lumen, for secretion and excretion?

Answer 12

NaHPO4-

H2PO4-

Question 13

Glutamine can enter the proximal tubule and form NH4+ and HCO3-. Then, NH4+ can leave into the tubule lumen via exchange with Na+ and can form (blank) and be excreted.

Answer 13

NH4Cl

Question 14

What is the biggest “job” the kidneys perform?

Answer 14

Reabsorption of filtered bicarb.

Question 15

When calculating reabsorption rate of bicarb, what should be considered?

Answer 15

Reabsorption rate = filtered load - excretion rate

BUT excretion rate is negligible

Question 16

Net acid excretion equation

Answer 16

NAE = TA + NH4+ - HCO3 in the urine = new HCO3- generation

Question 17

Net acid excretion is equal to (blank)

Answer 17

The amount of new HCO3- generated. Acid is secreted at the same rate of formation of new bicarb.

Question 18

Amount of new HCO3 in mmol added to body per day under normal conditions.

Answer 18

59mmol/day

Question 19

In acidosis, amount of new HCO3 in mmol added to body per day.

Answer 19

200mmol/day

Question 20

In alkalosis, amount of new HCO3 in mmol lost from body per day.

Answer 20

-80mmol/day

Question 21

Which is greater: reabsorbed or new bicarbonate?

Answer 21

Reabsorbed bicarbonate FAR EXCEEDS new bicarbonate.

Question 22

Is more H+ secreted or excreted?

Answer 22

The amount of H+ secreted FAR EXCEEDS the amount of H+ excreted.

Question 23

How to measure fixed acid in the urine?

Answer 23

Titratible acid is determined by titrating urine back to pH 7.4. The amount of OH required to get pH back up to 7.4 will give you the amount of titratible acid.

Question 24

About how much H+ combined with NH3 is excreted in diabetic acidosis? How about H+ as titratible acid?

Answer 24

LOTS (tenfold!)

Kind of a lot!

Question 25

About how much H+ combined with NH3 is excreted in chronic renal disease? How about H+ as T.A.?

Answer 25

Hardly any - a low amount :( | Normal amount

Question 26

When using loop diuretics (K+ losing), will you experience hypo or hyperkalemia? Alkalosis or acidosis?

Answer 26

Hypokalemia; alkalosis

Question 27

When using K+ sparing diuretics (amiloride), will you experience hypo or hyperkalemia? Alkalosis or acidosis?

Answer 27

Hyperkalemia; acidosis

Question 28

What determines the lowest possible urine pH in the distal nephron?

Answer 28

Gradient for H+ ions in distal nephron

Question 29

Does the extent of HCO3- reabsorption determine the lowest possible tubular pH?

Answer 29

NO! Although H+ secretion and tubular pH fuel bicarbonate (HCO3-) reabsorption this process is virtually complete at tubular pH values greater than 4.4

Question 30

An increase in luminal carbonic anhydrase activity would enhance the production of (blank) and hence the reabsorption of (blank)

Answer 30

CO2 | HCO3-

Question 31

Normal range for anion gap?

Answer 31

8-16 mEq/L

Question 32

``` The anion gap is useful for the differential diagnosis of (blank). Thus, conditions which lead to (blank) can be divided into those which change the anion gap and those which do not. ```

Answer 32

Metabolic acidosis; metabolic acidosis

Question 33

A change in the anion gap is produced by conditions in which an unmeasured (blank) is introduced into the body.

Answer 33

anion

Question 34

If HCO3- or Cl- DECREASE what happens to the anion gap?

Answer 34

It becomes larger! More cation than anion!

Question 35

As lactic acidosis develops, (blank) buffers the excess H+ and is lost, while lactate (A-) concentration in the body increases to replace the lost (blank)

Answer 35

HCO3-; HCO3-

Question 36

Ingesting NH4Cl results in HCl formation. The excess acid is buffered by (blank) resulting in loss of (blank) and a proportionate gain of Cl-. Since the increase in Cl- counterbalances the loss in (blank) in the anion gap equation, will there be a net change in anion gap?

Answer 36

HCO3-; HCO3-; HCO3-; NO

Question 37

Things that might occur with chronic K+ deficiency (HYPOKALEMIA)

Answer 37

Low K+ will cause K+ to leave cells, and H+ to enter. a. high plasma pH b. neutral or acidic urinary pH c. elevated plasma bicarbonate levels d. low intracellular pH

Question 38

When bicarb rises, Cl- will likely do what?

Answer 38

DECREASE. Reciprocal relationship.

Question 39

With hypokalemia, will plasma bicarbonate increase or decrease.

Answer 39

INCREASE. Think about it. K+ will spill OUT of cells, so H+ will ENTER cells and be "trapped" there. So, cannot exchange for Bicarb.

Question 40

Hypokalemia results in a shift of K+ out of cells, and a shift of H+ into cells. This loss of H+ from the extracellular compartment will lead to what?

Answer 40

Metabolic alkalosis

Question 41

Unless some other complicating factor is involved (e.g., introduction of a foreign anion) the plasma concentrations of HCO3- and chloride (Cl-) vary in opposite directions to one another (i.e., as one goes up the other goes down). Thus during hypochloremia a (blank) in plasma HCO3- concentration is expected.

Answer 41

increase

Question 42

What condition can result in a decreased plasma bicarbonate?

Answer 42

diabetic ketoacidosis

Question 43

Is phosphate secreted in the proximal tubule?

Answer 43

NO

Question 44

Does diabetic ketoacidosis cause hypo or hyperkalemia?

Answer 44

Hyperkalemia!

Question 45

Would diarrhea cause hyperkalemia?

Answer 45

No! Loss of bicarb, so build up of H+. This will cause K+ stores to be depleted.

Question 46

If you throw up lots, what will happen to pCO2?

Answer 46

You will have alkaline plasma pH, so breathing rate will decrease and pCO2 will rise a bit to compensate.

Question 47

One characteristic of renal failure is the inability to excrete sufficient (blank).

Answer 47

Acid. This leads to a decrease in pH, and will increase respiratory rate to eliminate some CO2.