Epithelial Transport Flashcards
What is the normal plasma volume?
3L
What is the normal volume of lymph?
100ml
Give the free ion distribution across cell membranes
Outside = Na (133-146), Cl (95-108), Ca (2.1-2.6), K (3.5-5.3)
Inside = Na (10-12), Cl (4.2), Ca (10^-7), K (140-155)
What is the role of primary active transport in the nephron?
Sets up Na/K gradients
Describe Na+ reuptake by the thick ascending limb
Na/K ATPase creates gradient via capillary
NKCC2 (Na K Cl co-transporter) able to take Na from the tubular fluid
ROMK (renal outer medullary potassium channel) K into the tubular fluid
Where do loop diuretics work?
On NKCC2 in the thick ascending limb
Block Na reuptake therefore excreting more fluid
Describe Na+ reuptake by the distal convoluted tubules?
Na/K ATPase creates gradient via capillary
NCCT (Na Cl co-transporter)
ENaC (epithelial channel) electrochemical gradient taking Na from tubule fluid
Which drugs work on the DCT and which pumps are involved?
Thiazides = block NCCT
Amiloride = block ENaC
Block Na reuptake, therefore, excreting more fluid
Describe Na+ reuptake by the cortical collecting duct
Na/K ATPase creates gradient via capillary
Aquaporin = water uptake
ENaC = Na uptake
CIC = chlorine uptake
ROMK = K removal
What hormones act on the cortical collecting duct?
ADH = enhances aquaporins
Aldosterone = enhances ENaC and ROMK
Which drugs work on the cortical collecting duct and which pumps are involved?
Spironolactone = acts as aldosterone antagonist therefore inhibiting ENaC and ROMK
Amiloride = block ENaC
Block Na reuptake therefore excreting more fluid
Describe Na+ and bicarb reuptake in the early proximal tubule
Na pump = sets up the Na+ gradient
NHE (Na/H exchanger) = H combines and forms carbonic acid, that then dissociates, CO2 is then absorbed, carbonic acid is reformed which splits to form the original H and bicarb
Anion exchanger = bicarb in for Cl out
Which drugs work on the early proximal tubule and which pumps are involved?
Amiloride = blocks NHE
Block Na reuptake therefore excreting more fluid
Outline Cl reabsorption in the proximal tubule
Na pump sets up Na gradient
NHE = removes H, forms formic acid which goes back into the cell, then forms formate
Anion exchanger = removes formate from the cell but puts Cl into the cell
How can Cl move through tight junctions?
Going down the tubule the conc of Cl increases = high enough conc for it to move through tight junctions into the cell
Describe phosphate reuptake in the proximal tubule
Na/K ATPase creates gradient via capillary
Na dependent phosphate transporter = co-transports 2Na in with 1Pi in
Phosphate conc rises and passively diffuses into the capillary
Phosphate reuptake in the proximal tubules is hormonally regulated by what?
PTH
Vit D
How does glucose reuptake into the proximal tubules take place?
Na/K ATPase creates gradient via capillary
SGLT2 (Na-Glucose transporter 2) into cell
GLUT2 from cell to capillary
As glucose conc rises all the transporters become saturated and more is seen in the urine
How does AA reuptake into the proximal tubule occur?
Na/K ATPase creates gradient via capillary
Na-dependent AA transporter
Passive AA transporter into the capillary
How does urea reuptake into the proximal tubule occur?
Na/K ATPase creates gradient via capillary
Na-dependent urea transporter
Passive urea transport into the capillary
Outline receptor-mediated endocytosis
Ligand binds ligand
Coated pit created
Pinches off
Uncoated vesicle fused with lysosome
Dissociation of receptor
E.g. Albumin, vit B12 via transcobalamin, vit D3,
Describe Ca2+ reuptake in the proximal tubule
TRPV6 Ca channels = into the cell
Na/K ATPase creates gradient via capillary
NCX = Na/Ca exchanger into the capillary
How is K secreted in the thick ascending limb?
ROMK (renal outer medullary K channels)
Blocked by spironolactone = less water secreted
How are organic acids secreted in the proximal tubule?
Acid-base antiporter
