7.2 Renal acid-base control Flashcards
What pH indicates acidosis and alkalosis
Acidosis: 7.35
Alkalosis: 7.45
What are the three levels of protection of influx of acid
Chemical buffering
Respiratory response
Renal response
What are the two mechanisms of making HCO3-
- Produced during titration of urinary buffers
2. Synthesis of NH4+ by the kidney produces HCO3-
What is the process of titration of filtered HCO3-? (reabsorption) H
CO2 and H2O get converted to H+ and HCO3- by carbonic anhydrase. H+ will be actively pumped across the apical membrane into the tubular fluid and bind to a buffer to be excreted. The HCO3- will be exchanged with Cl on the basolateral membrane into the blood.
how is HCO3- reabsorption regulated?
The H+ gradient (as well as expression of the transporters)
What happens to the transporters in acidosis?
The H ATPase will be upregulated in the collecting duct
NA/H antiporter and Na/3HCO3- in the proximal tubule will be upregulated
How is filtered HCO3- reabsorbed in the proximal tubule?
H+ efflux into the tubular fluid occurs via H ATPase and mainly the Na/H antiporter. The H+ couples with HCO3- to form H2CO3. This H2CO3 is converted by CA to H2O and CO2 which is able to diffuse across the apical membrane. Once in the cell the H2O and CO2 are converted into HCO3- and H+ by CA. The H+ is then recycled out into the tubular fluid while the HCO3- is able to move across the basolateral membrane via the Na/3HCO3 symporter and the HCO3-/Cl exchanger.
How is HCO3- secreted in the collecting duct and when does this occur?
occurs only in metabolic alkalosis
H2O and CO2 enter via teh basolateral membrane. These are converted by CA into HCO3- and H+. The HCO3- wil be transported into the tubular fluid via the HCO3-/Cl- antiporter. The H+ is pumped out of basolateral membrane via the H+ ATPase
What is the purpose of creating new HCO3-
To replace that which was lost during neutralization of the non volatile acids produced during metabolism (formation of titratable acid)
where is the main site of HCO3- production and how is it produced?
Proximal tubule from the synthesis of NH4+
How is HCO3- produced in the proximal tubule?
Glutamine enter via Na/Glutamine co-transporter. This enters the mitochondria. The glutamine is broken down by glutaminase into NH4+ and glutamate. The NH4+ exits teh mitochondria. The glutamate will form alpha ketoglutarate (glutamate dehdrogenase) - this reatcion will produce another NH4. The 2 NH4+ molecules will form 2NH3 and 2H+ which are transported across the apical membrane. Meanwhile the alpha ketoglutarate combines with 2 H+ to form 1/2 glucose . The consumption of 2H+ is equivalent to forming 2 HCO3- ions.
When will the urine anion gap be zero/slightly positive and when will it be negative?
Zero/slightly positive = normal NH4 production
Strongly negative = increased NH4 production
