Acid-base regulation

Question 1

what is the henderson-hasselbalch equation for the bicarbonate buffer system?

Answer 1

pH = 6.1 + log [HCO3-] / (0.03) x PCO2)

Question 2

what largely determines blood pH?

Answer 2

RATIO of bicarbonate ion to dissolved CO2

Question 3

how does the kidney regulate acid-base biochemistry?

Answer 3

• H+ excretion

- bicarb reabsorption

Question 4

how are protons removed from the body?

Answer 4

• filtered buffers (phosphate buffers)

- binding to NH3 (NH4+)

Question 5

what transporter proteins are located at the PCT?

Answer 5

• luminal Na/H exchanger (protons into lumen)

- basolateral Na/K ATPase (3 Na reabsorbed, 2 K into cell)

Question 6

what transporter protein is located at the DCT?

Answer 6

proton ATPase (protons into lumen)

Question 7

what happens at the DCT in response to low pH?

Answer 7

insertion of ATPase into luminal membrane (more protons enter tubular fluid)

Question 8

what % of bicarb is reabsorbed at the PCT? what % is reabsorbed at the collecting tubule?

Answer 8

• 90% at PCT

- 10% at collecting tubule

Question 9

what are the steps of bicarb reabsorption at the PCT? what is the net effect?

Answer 9

• protons secreted into tubule lumen
• reacts with bicarb in filtrate, forming carbonic acid
• carbonic anhydrase converts carbonic acid to water and CO2
• water and CO2 diffuse into renal tubular cell
• carbonic anhydrase converts water and CO2 to carbonic acid
• carbonic acid dissociates, protons exported to tubule lumen and bicarb exported to blood

NET EFFECT: movement of NaHCO3 from filtrate to blood

Question 10

what are the steps of bicarb reabsorption at the collecting duct? what is the net effect?

Answer 10

• formation of carbonic acid in tubular lumen
• water and CO2 re-enter tubular cell
• carbonic acid is re-made in tubular cell
• dissociation to bicarb and proton in tubular cell
• bicarb reabsorbed by a chloride-bicarb transporter

pumping out proton, which forms carbonic acid, acted upon by carbonic anhydrase, CO2 and water are taken back up

Question 11

what is the difference between bicarb reabsorption betwee nthe PCT and collecting duct?

Answer 11

• different way to put proton in the tubular lumen

- different pump putting bicarb back into system

Question 12

where are beta intercalated cells located? what is special about them?

Answer 12

• collecting duct

- reverse polarity of membrane transporters

Question 13

what are the transporters in beta intercalated cells?

Answer 13

• HCO3 / Cl

- H+ ATPase

Question 14

what is the limiting urine pH? what cant it be lower?

Answer 14

4.4

the proton translocator cannot pump any more protons into lumen

Question 15

what is the main non-bicarb urinary buffer? what form is excreted?

Answer 15

• phosphate

- H2PO4 -

Question 16

the ability to excrete protons as H2PO4 - is limited by:

Answer 16

• amount of HPO4 in filtrate

- requirement of body to retain phosphate

Question 17

for each newly formed H2PO4 excreted into the urine, what happens to 1) proton, and 2) bicarb?

Answer 17

• one proton eliminated

- one new bicarb formed and added to the blood

Question 18

where in the kidney does ammonia formation occur?

Answer 18

tubule cells

Question 19

what enzyme is expressed by the kidney allowing it to convert glutamine to glutamate?

Answer 19

glutaminase

Question 20

what happens to glutamate after being converted from glutamine from glutaminase? what is the net effect?

Answer 20

converted to a-ketoglutarate and ammonia by glutamate dehydrogenase

NET EFFECT: ammonia exported to tubular lumen, bicarb released to the blood - excretion of protons into the lumen and addition of NEW molecules of bicarb to the blood

Question 21

how many bicarb ions are formed from glutamate?

Answer 21

2

Question 22

what happens to ammonia excretion in repose to increased urine acidity?

Answer 22

rapid increase

Question 23

the rate of proton secretion is dependent on _____

Answer 23

pH

Question 24

what does a reduced pH do to the Na/H antiporter and H+ ATPase?

Answer 24

activation

Question 25

what happens to ammonia formation during acidosis?

Answer 25

increase

Question 26

what happens to 1) glutamine uptake / glutaminase activity, and 2) ammonia excretion during acidosis?

Answer 26

increase

Question 27

during alkalosis, proton secretion is _________ (sufficienct / insufficient) to allow bicarb reabsorption

Answer 27

insufficient

Question 28

what happens to bicarb during alkalosis?

Answer 28

excreted in urine

Question 29

what is the effect of beta intercalated cells during alkalosis?

Answer 29

actively SECRETE bicarb into tubular lumen

Question 30

how is arterial bicarb calculated?

Answer 30

• from concentration of CO2 and pH

Question 31

what is the equation for anion gap?

Answer 31

[Na]plasma - ([HOC3]plasma + [Cl-]plasma)

Question 32

what is base excess or deficit (delta base)?

Answer 32

difference between measured [HCO3-] and [HCO3-] predicted by the normal buffer slope at that pH