The Collecting Duct Flashcards
What are the two main cells in the collecting duct?
Principal cells and intercalated cells
What is the role of principal cells?
Regulating salt and water concentrations
What is the role of intercalated cells?
Acid-base homeostasis regulation
Describe the ion movement in the distal convoluted tubule
A sodium gradient is set up across the basolateral membrane via Na/K/ATPase
Sodium and chloride is cotransported across the apical membrane
Chloride the diffuses via facilitated diffusion out of the cell
Describe the ion movement in the collecting duct principal cells
A sodium and potassium gradient is set up across the basolateral membrane via Na/K/ATPase
Sodium is reabsorbed by ENaC channels
Potassium is secreted and moves out across the basolateral membrane via ROMK channels
How does aldosterone alter principal cell ion movement?
Increases activity and abundance of Na/K/ATPase, ENaC and ROMK channels
Why is the potassium channel coupling in the collecting duct needed to aid sodium transport?
Sodium reabsorption would depolarise the cell and slow export if not for potassium secretion
How does increased tubular flow increase sodium entry?
Increased flow bends cilia on the apical membrane
The bending of the cilia increases calcium entry by activating PKD1/2
Calcium entry activates ROMK channels
Increased potassium secretion allows for increased sodium reabsorption
Describe the process of calcium reabsorption
Can diffuse paracellularly
Diffuses via TRPV5/6 channels
Is exported over basolateral membrane via Ca ATPase or Na/Ca exchanger
Absorbed by calbindin
What effect does parathyroid hormone have on calcium reabsorption? How?
Increases reabsorption
Increases TRPV5/6 activity
What effect does vitamin D have on calcium reabsorption? How?
Increases reabsorption
Increases abundance of TRPV5/6 and calbindin
Describe the effect of antidiuretic hormone
Increases vesicular exocytosis of aquaporins and urea transport proteins
Increases water rand urea reabsorption
What do alpha intercalated cells secrete? Describe the process
Protons
Carbonic anhydrase converts water and carbon dioxide into proton and bicarbonate
The proton is pumped out via K/H/ATPase and H/ATPase
The proton is combined with bicarbonate in the lumen via carbonic anhydrase
What do beta intercalated cells secrete? Describe the process
Bicarbonate ions
Ions are produced by carbonic anhydrase and exchanged for chloride
