Renal Physiology: Acid Base

Question 1

Blood Buffer pH equation…

Answer 1

pH = 6.1 + log [bicarb] / (0.03 x PCO2)

Question 2

A 1 unit change in pH indicates a ___-fold increase in hydrogen ion concentration

Answer 2

10x

Question 3

13,000 - 20,000 mEq/day of volatile acid is handled by ______ and excreted as_____

Answer 3

lungs as CO2

Question 4

Non-volatile, or fixed, acids are handled by…

Answer 4

the kidney

Question 5

What is responsible for 75% of fixed acid production?

Answer 5

methionine and cysteine catabolism forming sulfuric acid

Question 6

What are the primary intracellular buffers?

Answer 6

proteins

Phosphate

Question 7

Mass action rule notes that for every ________ increase in PCO2, bicarb will increase by _______

Answer 7

10 mmHg PCO2 increase

1 mEq/L bicarb increase

Question 8

Mass action rule notes that for every ________ decrease in PCO2, bicarb will decrease by _______

Answer 8

10 mmHg PCO2 decrease

2 mEq/L bicarb decrease

Question 9

What regulates respiration?

Answer 9

plasma PCO2

Question 10

By what 3 mechanisms do the kidneys keep bicarb steady between 22-26?

Answer 10

complete recovery of filtered bicarb when over 26

synthesis above GFR

Excretion when excess

Question 11

What drives bicarb recovery in the nephron?

Answer 11

secretion of hydrogen ions

Question 12

In the PT, H+ is __________ and in the DT H+ is ________

Answer 12

H+ - sodium exchange (NHE) in PT

Active secretion in DT

Question 13

Bicarbonate is most absorbed in the _____ (x%), then the _____ (x%), and then the _____ (x%)

Answer 13

PT (85%)

Ascending thick limb (10%)

Collecting duct (5%)

Question 14

What percent of filtered bicarb is reabsorbed?

Answer 14

99.9%

Question 15

What two hormones, when acting on the PT, increase bicarb reabsorption?

Answer 15

AT II

Aldosterone

Question 16

This hormone, when active in the PT:

increases expression of sodium-hydrogen exchanger, which pumps hydrogen from ICF to lumen, allowing Bicarb to be transported to the ECF via sodium cotransport

Answer 16

AT II

Question 17

This hormone, when active in the PT:

increases expression of H+ ATPase, which pumps hydrogen from ICF to lumen, allowing Bicarb to be transported to the ECF via sodium cotransport

Answer 17

Aldosterone

Question 18

What enzyme catalyzes the reaction of water and carbon dioxide to form hydrogen ions and bicarb?

Answer 18

carbonic anhydrase

Question 19

This hormone, when active in the alpha-intercalated cells of the CD:

Increases expression of the H+-ATPase which pumps hydrogen from ICF to lumen, allowing Bicarb to be transported to the ECF via chloride cotransport

Answer 19

aldosterone

Question 20

hydrogen ions leave the PT tubule cells by what two mechanisms?

Answer 20

Sodium - Hydrogen Exchanger

H+-ATPase

Question 21

Hydrogen ions leave the alpha intercalated cells of the CD by what two mechanisms?

Answer 21

H+-ATPase

H+-Potassium Exchanger

Question 22

Bicarb leaves the alpha intercalated distal tubule cell for reabsorption via what mechanism?

Answer 22

bicarb-chloride exchanger

Question 23

Bicarb leaves the tubule cell of the PT via what two mechanisms?

Answer 23

Sodium-Bicarb cotransport

Bicarb-chloride exchange

Question 24

for every bicarb neutralized in the tubule, ___ bicarb(s) is/are released into the PTC…

Answer 24

1

Question 25

luminal pH may drop as low as ____ once bicarb is absent from filtrate

Answer 25

4.5

Question 26

How is the kidney able to release more bicarb to the PTC than is present in the filtrate?

Answer 26

phosphate and NH3 accept H+ in the tubule to allow secretion of H+, and release of bicarb to PTC

Question 27

Describe the mechanism by which bicarbonate can be produced in the distal nephron…

Answer 27

H20 + CO2 –> Carbonic acid
(catalyzed by carbonic anhydrase)

In order for carbonic acid to enter the tubule, there must be a non-bicarb buffer (PO4, NH3)

H+ crosses apical border to tubule, binds with NH4+ or PO4, and bicarb free to enter PTC

Question 28

In the PT, Glutamine becomes ____ and _____ via glutaminase.

NH4+ splits to NH3 and hydrogen, they both diffuses to the lumen (together/separate?), where they are rejoined as NH4+

AKG is converted to ______, and is cotransported to the PTC with ______

Answer 28

AKG and NH4+

NH3 and H+ diffuse to lumen separately

AKG converted to bicarb

Cotransported with sodium

Question 29

1 glutamine will yield ___ bicarbs and ____ NH4+s

Answer 29

2

Question 30

What regulates synthesis of NH4+ from glutamine?

Answer 30

pH

Question 31

acidosis _____ glutamine catabolism…

Answer 31

increases

Question 32

What is the primary mechanism for dealing with chronic acid loads?

Answer 32

synthesis of NH4+ from glutamine