Acid-base regulation Flashcards
what is the henderson-hasselbalch equation for the bicarbonate buffer system?
pH = 6.1 + log [HCO3-] / (0.03) x PCO2)
what largely determines blood pH?
RATIO of bicarbonate ion to dissolved CO2
how does the kidney regulate acid-base biochemistry?
- H+ excretion
- bicarb reabsorption
how are protons removed from the body?
- filtered buffers (phosphate buffers)
- binding to NH3 (NH4+)
what transporter proteins are located at the PCT?
- luminal Na/H exchanger (protons into lumen)
- basolateral Na/K ATPase (3 Na reabsorbed, 2 K into cell)
what transporter protein is located at the DCT?
proton ATPase (protons into lumen)
what happens at the DCT in response to low pH?
insertion of ATPase into luminal membrane (more protons enter tubular fluid)
what % of bicarb is reabsorbed at the PCT? what % is reabsorbed at the collecting tubule?
- 90% at PCT
- 10% at collecting tubule
what are the steps of bicarb reabsorption at the PCT? what is the net effect?
- 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
what are the steps of bicarb reabsorption at the collecting duct? what is the net effect?
- 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
what is the difference between bicarb reabsorption betwee nthe PCT and collecting duct?
- different way to put proton in the tubular lumen
- different pump putting bicarb back into system
where are beta intercalated cells located? what is special about them?
- collecting duct
- reverse polarity of membrane transporters
what are the transporters in beta intercalated cells?
- HCO3 / Cl
- H+ ATPase
what is the limiting urine pH? what cant it be lower?
4.4
the proton translocator cannot pump any more protons into lumen
what is the main non-bicarb urinary buffer? what form is excreted?
- phosphate
- H2PO4 -
the ability to excrete protons as H2PO4 - is limited by:
- amount of HPO4 in filtrate
- requirement of body to retain phosphate
for each newly formed H2PO4 excreted into the urine, what happens to 1) proton, and 2) bicarb?
- one proton eliminated
- one new bicarb formed and added to the blood
where in the kidney does ammonia formation occur?
tubule cells
what enzyme is expressed by the kidney allowing it to convert glutamine to glutamate?
glutaminase
what happens to glutamate after being converted from glutamine from glutaminase? what is the net effect?
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
how many bicarb ions are formed from glutamate?
2
what happens to ammonia excretion in repose to increased urine acidity?
rapid increase
the rate of proton secretion is dependent on _____
pH
what does a reduced pH do to the Na/H antiporter and H+ ATPase?
activation
what happens to ammonia formation during acidosis?
increase
what happens to 1) glutamine uptake / glutaminase activity, and 2) ammonia excretion during acidosis?
increase
during alkalosis, proton secretion is _________ (sufficienct / insufficient) to allow bicarb reabsorption
insufficient
what happens to bicarb during alkalosis?
excreted in urine
what is the effect of beta intercalated cells during alkalosis?
actively SECRETE bicarb into tubular lumen
how is arterial bicarb calculated?
- from concentration of CO2 and pH
what is the equation for anion gap?
[Na]plasma - ([HOC3]plasma + [Cl-]plasma)
what is base excess or deficit (delta base)?
difference between measured [HCO3-] and [HCO3-] predicted by the normal buffer slope at that pH
