Acid-Base Homeostasis Flashcards
K+ secretion is controlled by ________ and ______.
[K+]; aldosterone!!
Excretion of potassium ranges from — to —% of all filtered amounts.
1% - 110%
Principal cell
K+ secretion
KCC, K+ channels (as well as ENaC)
Active uptake, passive diffusion to urine.
α-intrecalated cells
Only reabsorb potassium.
H+, K+ ATPase in apical membrane
Active transport from urine to cell, passive diffusion to blood.
α-intercalated cells provide ______ reabsorption.
Constant!
Principal cells provide ________ excretion.
HIGHLY variable!
(works most when K+ is high)
Stimulation of K+ secretion by plasma K+
Na/K ATPase activity inc
Apical K+ channel activity inc
Aldosterone secretion from the adrenal cortex
Aldosterone on K+ secretion
Increases Na/K ATPase activity
Increase ENaC expression (increases driving force)
Increase in apical K+ permeability
Contribution of diet and metabolism to plasma pH
Introduction of amino acids, fatty acids
Production of CO2, lactic acids, ketoacids.
Leads to decrease in pH
Contributors to balancing plasma pH
Volatile acids (CO2) in respiration, fixed acids in urine.
Overall CA reaction equation
CO2 + H2O <—> HCO3- (bicarbonate) + H+
pKa of CO2/HCO3-
6.1, almost all in bicarbonate in the blood pH
Phosphate pKa
6.8, much closer to that of blood but much lower concentration in biological fluids.
Concentrations of HCO3- and CO2 are tightly regulated by the _____ and _____, respectively.
Kidneys; lungs!!
(through reabsorption/(excretion of H+), and expiration)
Most HCO3- is reabsorbed in the ________ (__%)
Proximal tubule; 87%!!
Process from NHE excretion of H+ to K+ reabsorption in the proximal tubule
H+ excretion meets with urine HCO3-, pushes towards CO2/H2O which can then enter the cell. Cellular CO2/H2O is converted by enzyme carbonic anhydrase into HCO3- which then leaves at the basolateral membrane through active transport.
NBC secondary active
Cotransport of Na and HCO3- into the blood.
In proximal tubule
AE transporter
Anion exchanger that moves Cl- into the cell and HCO3- out into the blood
In proximal tubule
α-intercalated cells in HCO3- regulation
Use H+ ATPase on the apical membrane and AE1 (anion exchanger) on the basolateral membrane to cause bicarbonate reabsorption.
β-intercalated cells in HCO3- regulation
HCO3- secretion through Pendrin on the apical membrane and H+ ATPase on the basolateral membrane.
Pendrin
Another anion exchanger targeted to the apical membrane of β-intercalated cells, Cl- in, HCO3- out.
Main two buffers of the urine
- titratable acids
- NH4+ (ammonium)
H2PO4 as a titratable acid
HPO4(2-) takes up H+, excrete in the form of H2PO4(1-)
Titratable acids
organic buffers found in the distable tubule and collecting duct that take up the H+ protons as they are secreted from β-intercalated cells.
