BIOC34H3 Lecture Notes - Lecture 21: Metabolic Acidosis, Tubular Fluid, Proximal Tubule

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BIOC34:(Lecture(20( ( Final(
Mar.%14,%2018%
84%
Acid-Base%Balance"
Acid-Base*Regulation*by*Renal*System*
During%metabolic%acidosis,%the%kidney:%
o Increases%HCO3-%reabsorption%
o Increases%H+%secretion%
o Synthesizes%HCO3-%
In%response%to%metabolic%alkalosis,%the%kidney:%
o Decreases%HCO3-%reabsorption%
o Decreases%H+%secretion%
Acidosis*in*the*Proximal*Tubule*
When%blood%pH%is%acidic,%HCO3-%
that’s%been%filtered%into%the%
tubular%fluid%reacts%with%
secreted%H+%to%form%H2CO3%
which%is%converted%into%H2O%
and%CO2%by%CA(catalysis%
The%CO2%diffuses%into%the%
epithelial%cell%and%is%converted%
to%H+%and%HCO3%once%more%by%
CA%along%with%another%H2O%
The%H+%is%returned%to%the%tubular%fluid%to%react%with%another%HCO3-%while%
HCO3%is%transported%into%the%peritubular%fluid%with%Na/HCO3%co-transporters%
and%Cl/HCO3%antiporters%
Overall:%
o HCO3-%is%reabsorbed%into%the%plasma%
o H+%is%secreted%into%the%tubular%fluid%and%excreted%as%H2O%
o Na+%is%reabsorbed%as%
well%
Acidosis*in*Distal*Tubule*and*
Collecting*Duct*
In%the%proximal%tubule,%all%of%
HCO3-%has%been%reabsorbed%
so%in%the%tubular%fluid%it%must%
be%synthesized%
CO2%diffuses%from%the%
peritubular%fluid%into%the%cell%
and%reacts%with%H2O%to%
produce%HCO3-%and%H+%
o The%HCO3%s%transported%into%peritubular%fluid%via%HCO3/Cl%anti-porter%
o The%Cl%transported%into%the%cell%is%transported%back%out%à%Cl%
recycling%
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Document Summary

Acid-base regulation by renal system: during metabolic acidosis, the kidney, increases hco3, increases h+ secretion, synthesizes hco3. In response to metabolic alkalosis, the kidney: decreases hco3, decreases h+ secretion. Ca along with another h2o: the h+ is returned to the tubular fluid to react with another hco3. Hco3 is transported into the peritubular fluid with na/hco3 co-transporters and cl/hco3 antiporters: overall: Is reabsorbed into the plasma: hco3, h+ is secreted into the tubular fluid and excreted as h2o, na+ is reabsorbed as well. Hco3 so in the tubular fluid it must be synthesized: co2 diffuses from the peritubular fluid into the cell and reacts with h2o to. And h+ produce hco3: the hco3 s transported into peritubular fluid via hco3/cl anti-porter, the cl transported into the cell is transported back out cl recycling. Final: the h+ is transported into the tubular fluid and reacts with hpo4.

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