[8] Placeholder Flashcards
Proximal Tubule Reabsorption
- Active transport Na creates intracellular (-) allowing intracellular movement of Na
- H+ is secreted into the lumen by Na-H Exchanger
- H+ combines with filtered HCO3 -> H2CO3 -> H2O + CO2
- CO2 diffuses into the cell to combine with H2O to form H2CO3 -> H+ + HCO3
Renal Threshold for Bicarbonate Absoprtion
25mM before it starts being excreted
Titratable Acid in Urine
H2PO4
What is responsible for forming Bicarbonate?
Distal Tubule
Function: Intercalated Cell
Secretes hydrogen ions into the filtrate
Function: Principal Cells
Hormonally regulated water and sodium reabsorption
Potassium secretion
Diffefence: Alpha and Beta Intercalated cells
A: H+ Excreted through H+-ATPase Pump
B: Active when you remove Bicarbonate
Two Characteristics of Hyperaldosterone
Hypokalemia
Hypertension
Secretion of H+ by the Alpha-Intercalated Cell at the Cortical Collecting Tubule
- Intracellular H2O and CO2 in the presence of Carbonic Anhydrase form H+ and HCO3-
- H+ secreted by an active H+ATPase Pump
- HCO3 returns to circulation via Cl-HCO3 exchanger
- Formation of NH4+
- Formation of Titrable Acid
Define: Ionic Trapping
Ammonia can freely leave the Collecting Duct because it is uncharged. Once this passes into the lumen, it combines with Hydrogen ions to become NH4+ and can no longer return
Differentiate NH3 and NH4+
NH3: Base Form, Uncharged, Permeable
NH4: Charged, Impermeable
Regulation of HCO3 reaborption
- Primary
- Secondary
P: Systemic Acid Base Balance
S:
- Increase in filtered load of HCO3
- Decrease in ECF volume
- Increase in Angiotensin II
- Hypokalemia
How to test the amount of H+ produced during HCO3 formation?
Titrate with Sodium Hydroxide until pH = 7.4
Fates of Secreted H+
90% Titrates filtered Bicarbonate in Reclamation
1% Buffered by NH3
1% Buffered by other Tubular Buffers, mostly HPO4
Minute amount remains free
