Renal diluting segments and collecting systems Flashcards
Where on the nephron is water permeable?
Proximal tubule
Descending Loop of Henle
Where on the nephron is water impermeable?
Ascending thin loop of Henle
Thick ascending loop of Henle
Early part of distal convoluted tubule
Where is permeability to water regulated by ADH?
late part of distal convoluted tubule
Collecting tubule
What aquaporin channel is found in the proximal tubule and descending loop of Henle?
AQP1
AQP7 - straight PT
What aquaporin channel is found in the late distal convoluted tubule and collecting tubule?
Constitutive AQP3 and AQP4 on basolateral
Facultative AQP2 on apical
Where is NaCl reabsorbed?
Thin and thick ascending limb
What is the conc of fluid leaving TAL compared to plasma?
Dilute
What is the driving force for transcellular transport in the TAL?
Basolateral Na+K+ATPase pump - maintains low intracellular Na+
What mediates Na+ movement across apical membrane of the TAL?
NKCC2 symporter (also expressed by macula densa cells)
What is essential for continued operation of NKCC2 symporter in the TAL?
K+ channels on apical membranes
What else mediates Na+ movement across apical membrane of TAL?
Na+-H+ antiporter
What other channels are present on the basolateral membrane of TAL?
Na+-HCO3- symporter
Cl- channels
K+Cl- channel
K= channels
What drives paracellular reabsorption in the TAL?
Lumen-positive potential driven by K+ channels on apical membrane
What cations does the TAL reabsorb?
Na+, K+, Mg2+ and Ca2+
How do loop diuretics work?
Increase volume of excreted urine by blocking Na+ reabsorption at specific sites
What loop diuretics block NKCC2?
Furosemide
Bumetanide
What maintains the low intracellular Na+ in the early DCT?
Na+-K+-ATPase pump
What mediates entry of NaCl across apical membrane in early DCT?
Na+-Cl- symporter
How does Cl- leave the cell in early DCT?
Via Cl- channels on basolateral membrane
What 2 cells are found in the late DCT and collecting ducts?
Principal and intercalated cells
What is the MoA of principal cells?
Reabsorb Na+. Cl- and water
Secrete K+
Dependent on Na+-K+-ATPase pump on basolateral membrane
What is the MoA of intercalated cells?
Reabsorb K+
Secrete H+ or HCO3-
Dependent on apical H+-K+ATPase pump
What channels absorb Na+ on the apical membrane of the late DCT and collecting duct?
ENaC channels
What is transported paracellularly in the late DCT and collecting ducts?
Cl-
What regions of the kidney and low water permeability without ADH?
Outer medullary and cortical regions
What triggers ADH production?
Hyper osmosis
What does ADH bind to in the late DCT and collecting ducts?
V2 receptor on basolateral membrane
What does the V2 receptor activate?
cAMP
Where is the AQP2 water channel expressed?
Apical membrane of late DCT and collecting ducts
How is water absorbed into the blood?
By osmosis via constitutively AQPs on basolateral membrane
