GMS 6401 STUDY QUESTIONS AND 100%
VERIFIED CORRECT ANSWERS!!
what is the most abundant extracellular cation?
Na+ ~140mEq/L
How much Na+ is filtered daily?
GFR= 120 mL/min ~1kg of Na+ is filtered daily (~24,000mEq)
How much of Na+ filtered is reabsorbed?
~99%
What is Na+ reabsorption essential for?
Volume homeostasis
Electrolyte balance
Driving reabsorption of other solutes and water
Luminal (Apical) Membrane
Function: for Na+ to enter passively
How does Na+ enter passively?
Cotransporters (e.g., Na+/glucose)
Exchangers (e.g., NHE3)
Channels (e.g., ENaC)
Basolateral (Peritubular) Membrane
,Na+ is actively pumped out by Na+/K+ ATPase, establishing the Na+ gradient
Tight Junctions
allow for paracellular Na+ movement (especially in proximal tubule)
How much Na+ gets reabsorbed the proximal tubule and what are the transporters?
65-70%
Transporters: NHE3, Na+/solute cotransporters
High water permeability
Bulk absorption; load dependent
How much Na+ gets reabsorbed at the thick ascending limb? What are the transporters?
20-25%
NKCC2, NHE3
Water Impermeable
Generates lumen (postive ve)
How much Na+ gets reabsorbed at the distal convoluted tubule? What are the
transporters?
~5%
Transporters: NCC (Na+Cl- cotransporter)
Water Impermeable
Thiazide-sensitive
How much Na+ gets reabsorbed at the collecting duct? What are the transporters?
, ~3-5%
Transporters: ENaC (epithelial Na+ channel)
Water permeability is ADH-dependent
Aldosterone-regulated
What transporterts are in the proximal tubule- early phase?
NHE3 (Na+/H+) exchanger: coupled with HCO3- reabsorption
Na+/Glucose cotransporter (SGLT): dependent on both sites being occupied
Other coupled transporters:
Na+/PO4 3-
Na+/amino acids
Na+/ lactate
What are the characteristics of the proximal tubule early phase?
Iso-osmotic reabsorption (H2O follows Na+)
High water permeability via aquaporins
Minimal Cl- reabsorption early on --> inc. Cl- concentration lumen
What is the mechanism of the proximal tubule- late phase?
Continued NEH3 activity
Cl-/anion exchanger enables transcellular Cl- reabsorption
High luminal Cl- concentration drives paracellular Cl- diffusion
Na+ follows via solvent drag and electrochemical coupling
What does early PT favor?
VERIFIED CORRECT ANSWERS!!
what is the most abundant extracellular cation?
Na+ ~140mEq/L
How much Na+ is filtered daily?
GFR= 120 mL/min ~1kg of Na+ is filtered daily (~24,000mEq)
How much of Na+ filtered is reabsorbed?
~99%
What is Na+ reabsorption essential for?
Volume homeostasis
Electrolyte balance
Driving reabsorption of other solutes and water
Luminal (Apical) Membrane
Function: for Na+ to enter passively
How does Na+ enter passively?
Cotransporters (e.g., Na+/glucose)
Exchangers (e.g., NHE3)
Channels (e.g., ENaC)
Basolateral (Peritubular) Membrane
,Na+ is actively pumped out by Na+/K+ ATPase, establishing the Na+ gradient
Tight Junctions
allow for paracellular Na+ movement (especially in proximal tubule)
How much Na+ gets reabsorbed the proximal tubule and what are the transporters?
65-70%
Transporters: NHE3, Na+/solute cotransporters
High water permeability
Bulk absorption; load dependent
How much Na+ gets reabsorbed at the thick ascending limb? What are the transporters?
20-25%
NKCC2, NHE3
Water Impermeable
Generates lumen (postive ve)
How much Na+ gets reabsorbed at the distal convoluted tubule? What are the
transporters?
~5%
Transporters: NCC (Na+Cl- cotransporter)
Water Impermeable
Thiazide-sensitive
How much Na+ gets reabsorbed at the collecting duct? What are the transporters?
, ~3-5%
Transporters: ENaC (epithelial Na+ channel)
Water permeability is ADH-dependent
Aldosterone-regulated
What transporterts are in the proximal tubule- early phase?
NHE3 (Na+/H+) exchanger: coupled with HCO3- reabsorption
Na+/Glucose cotransporter (SGLT): dependent on both sites being occupied
Other coupled transporters:
Na+/PO4 3-
Na+/amino acids
Na+/ lactate
What are the characteristics of the proximal tubule early phase?
Iso-osmotic reabsorption (H2O follows Na+)
High water permeability via aquaporins
Minimal Cl- reabsorption early on --> inc. Cl- concentration lumen
What is the mechanism of the proximal tubule- late phase?
Continued NEH3 activity
Cl-/anion exchanger enables transcellular Cl- reabsorption
High luminal Cl- concentration drives paracellular Cl- diffusion
Na+ follows via solvent drag and electrochemical coupling
What does early PT favor?
