Renal Respiratory Compensation/acid Base Status

Question 1

Respiration is regulated by __________

Answer 1

Plasma CO2

Question 2

How does CO2 regulate respiration?

Answer 2

CO2 diffuses across the BBB, forms with water, and the dissociated H+ will stimulate chemoreceptors of the medulla and increase respiration

(This will Lower the denominator in the Henderson hasselbach equation so pH goes up….there will be less PCO2 )

Question 3

How do kidneys stabilize HCO3?

Answer 3

1. Complete “recover” of filtered bicarb when HCO3 is below 26 (normal range is 22-26)
2. Synthesizing “new” bicarb beyond what was filtered in the nephron
3. Excreting HCO3 when its over 26

Question 4

How does the kidney “recover” HCO3?

Answer 4

1. Within the nephron cell, carbonic anhydrase forms H+ by splitting H2CO3 into H+ and HCO3-
2. The H+ is then either exchanged with Na+ in the lumen, or is actively secreted into the lumen.
3. The HCO3- will enter the capillary blood
4. The secreted H+ will react with HCO3- in the filtrate to form H2O and CO2 that can cross into the nephron cell

Question 5

Does HCO3- cross the apical membrane?

Answer 5

No

It must react with secreted H+ to form CO2 and H2O in order to cross the apical membrane

Question 6

Where does most of the HCO3- get reabsorbed?

Answer 6

Proximal tubule 85%

Ascending thick limb-10%

Collecting duct- 5%

Question 7

Does most of the HCO3- that gets filtered end up getting reabsorbed?

Answer 7

Yes, 99.9% gets reabsorbed

Question 8

What enzyme turns H2CO3 into H20 and CO2, and then once inside the cell turns those into H+ and HCO3-?

Answer 8

Carbonic anhydrase

Question 9

Why do you have to multiply the PCO2 by 0.03 when calculating pH?

Answer 9

.03 is a solubility constant

Question 10

What is the normal range of PCO2 and what would be the perfect value?

Answer 10

35-45

Ideal= 40

Question 11

What is the normal range for HCO3 and what is the perfect value?

Answer 11

22-26

Perfect= 24

Question 12

What is the normal range for pH and what is the perfect value’/

Answer 12

7.35-7.45

Perfect= 7.4

Question 13

When the kidney generates new bicarb, does it depend on how much bicarb was filtered out in the first place?

Answer 13

No

Question 14

Do we have a transporter on the apical surface to transport bicarb into the cell?

Answer 14

NO!!!!**

HCO3 does NOT cross the apical membrane***

Question 15

True or false:

Recovery of each bicarb in the proximal tubule depends on the secretion of an H+

Answer 15

Trueeeeee

Question 16

Do Angiontensin II and Aldosterone have a function in acid base balance?

Answer 16

No

Question 17

What is the primary difference between recovery of HCO3 in the proximal tubule vs in the collecting duct?

Answer 17

Proximal tubule: NHE and H+ ATPase both secrete H+ into the lumen

Collecting duct: “H+ ATPase” and “H+,K+ antiporter ATPase” secrete H+ into the lumen

There’s no NHE in collecting duct

There’s no H+, K+ antiporter ATPase in the proximal tubule

Question 18

Once all the HCO3 is gone form the filtrate, does the pH of the urine change?

Answer 18

Yes, it can drop as low as 4.5 as H+ keeps getting secreted.

Phospate and NH4+ buffer systems are in place to absorb extra H+ in the lumen and keep it from getting too acidic

Question 19

What is meant by “titratable acidity”?

Answer 19

Phosphate (which gets filtered out of plasma) floats around in the lumen and absorbs H+. Forms H2PO4

This allows for the synthesis of additional HCO3-

(This is not under physiological control)

Question 20

What is the pK of phosphate?

Answer 20

6.8 (excellent for buffering urine)

Question 21

What happens when you breakdown glutamine?

Answer 21

You get two NH3 and two α-ketoglutarate.

The NH3 diffuses into the tubular fluid, traps an H+ to form NH4+, and is lost in the urine

The α-ketoglutarate is metabolized to form two HCO3 that goes into the blood!

Question 22

Where does the metabolism of glutamate happen

Answer 22

Proximal tubule

Question 23

Each glutamine metabolized yields _______HCO3 and ________ NH4+

Answer 23

2 HCO3 (to blood)

2 NH4+ (lost in urine)

Question 24

What is meant by diffusion trapping?

Answer 24

It is when the NH3 formed from the breakdown of glutamate diffuses into the lumen and binds with an H+ to form NH4+.
The NH4+ is highly impermeable, and so the H+ is “trapped” in the lumen until you pee it out

Question 25

Every time a glutamine molecule is broken down you lose _______ H+ and gain _______ HCO3-

Answer 25

Lose 2 H+

Gain 2 HCO3-

Question 26

Is the breakdown of glutamine under physiological control?

Answer 26

Yes, it is regulated by intracellular pH (in the proximal tubule)

Question 27

What happens when intracellular pH gets too acidic in the proximal tubule?

Answer 27

The cell ramps up its glutamine catabolism to form additional HCO3- to be returned to the blood to neutralize the extra H+

Question 28

What is the body’s primary mechanism for dealing with chronic acid loads like Diabetic Ketoacidosis?

Answer 28

Glutamine catabolism

Question 29

HYPOkalemia will (stimulate/inhibit) glutamine catabolism

Answer 29

Stimulate

(Related to the H+/K+ exchange across cell membrane. Remember how if a K+ goes into a cell, a H+ will go out and vice versa? If there is not enough K+ in the blood, the cell will release K+ and take up H+. This increases the acidity inside the cell and stimulates the cell to break down more glutamine, and thus form more HCO3-.)

Question 30

HYPERkalemia will (stimulate/inhibit) glutamine synthesis

Answer 30

Inhibit

(The cell will take up excess K+ in exchange for the release of an H+. This makes the inside of the cell more alkaline and will inhibit the catabolism of glutamine, and the formation of HCO3-.)

Acidosis is often accompanied by hyperkalemia never ever forget it

Question 31

The majority of fixed acid produced in the body (DKA, lactic acid, etc..) will be handled by (NH4+/ titratable acid)

Answer 31

NH4+

The titratable acid (phosphate) is limited

Question 32

If someone has chronic kidney failure, will they be able to handle H+ load efficiently?

Answer 32

No, they won’t be able to filter enough phosphate as titratable acid or make enough NH3

Question 33

What is this:
Defect in HCO3 or CO2

No change in the other parameter

Answer 33

Uncompensated/pure state

Question 34

What is this:

Defect in either HCO3 or CO2

Other parameter is compensating (moving in the SAME direction)

Answer 34

Simple disturbance with compensation

Question 35

What is this:

both HCO3 and CO2 are moving in opposite directions

Answer 35

Mixed state

Both HCO3 and CO2 are contributing to the acid/base disturbance

Ex: a COPD patient with diabetes

Question 36

What is meant by mass action?

Answer 36

When PCO2 changes, it will automatically cause a small change in HCO3 due to mass action. Nothing to do with compensation.

This has to do with the balance of this formula:
CO2+H2O HcCO3 H+ + HCO3

Question 37

How do you calculate mass action?

Answer 37

For every 10 mm that CO2 increases= HCO3 goes up by 1

For every 10 mm that CO2 decreases=HCO3 decreases by 2

(You need to add the 1 or 2 to 24! The expected normal value of HCO3, not the HCO3 that you are seeing in the patient right now.)

Question 38

When is calculating the mass action most helpful?

Answer 38

When you have a bicarb that is just barely outside of 24, and you aren’t sure if metabolic compensation is even happening, or if it’s just due to mass action.

Obviously if your bicarb was 18, that is a profound change and the body is definitely compensating

Question 39

If your patient’s pH is 7.38, is that considered an acidosis? They are in the normal range of 7.35-7.45!

Answer 39

Yes, this is considered an acidosis because they are still under 7.4. BUT it is considered completely compensated, since they are still in the normal range.

Question 40

Where will aldosterone stimulate H+ ATPase?

Answer 40

The proximal tubule

Not in the collecting duct