Flashcards in Week 4 - Plasma Volume Deck (36)
Why must Na excretion be able to change in the kidney?
-In order to maintain Na balance and match ingestion to excretion
Why must water and salt be added/removed together?
-If you removed one or the other you would change the osmolarity of plasma so addition/removal needs to be isotonic
What effect does osmotic and hydrostatic pressure of the peritubular capillaries have on Na reabsorption in PCT?
-If they are reduced it promotes Na and water reabsorption
-If they are increased it inhibits Na and water reabsorption
What are the target cells of aldosterone?
-Principle cells of late DCT and CD
What is the connection between Na and Cl reabsorption?
-NaKATPase on basolat geeratea Na gradient
-Na resorption occurs down its gradient with Cl accompanying it to maintain electro-neutrality
Name the transporters found in the PCT?
Name the transporter of LoH?
Name the transporter of DCT
Name the transport channel of late DCT and CD
Why is it significant that the tubular cells are polarised?
-Stop transporters from switching membranes
What governs uptake of solutes into peritubular capillaries?
What is the difference between S1 of PCT and S2?
-Different apical Na transporters
What transporters are involved in S1 of pct?
-NaKATPase and NaHCO3 on basolat
-NHE, Na:glu, Na:a'a and NaPi on apical
What happens to the concentration of Cl and Urea in S1? What affect does this have on S2?
-Increases to compensate for loss of glucose
-Creates a conc gradient for chloride reabsorption in S2-3
What transporters are involved in S2 of pct?
-NaKATPase on basolat
-NHE, paracellular Cl-, Transcellular Cl-
What drives water reabsorption into peritubular capillaries?
-Osmotic gradient caused by solute reabsorption
-Hydrostatic force of interstitium
-Oncotic pressure in peritubular capillary
What is glomerulotubular balance?
-A mechanism to control Na excretion in proportion to the volume of ultrafiltrate
-ie Blunts Na excretion response to any GFR change ->67% of Na in PCT always resorbed regardless of volume of ultrafiltrate
How is the medulla specialised for H2O reabsorption? What does this achieve?
-Has an increasing osmolarity into the medulla so water is drawn out of descending limb of loop of henle creating a hyperosmotic filtrate at the bottom of the loop
Why is it significant that the filtrate is hyperosmotic at the bottom of the loop of henle?
-Creates a concentration gradient for solutes so they can be pumped out of the ascending limb
Which limb in the loop of henle is impermeable to water?
Describe Na reabsorption in the ascending limb of loop of henle
-Na reabsorption is passive in the thin ascending limb through paracellular means
-Na reabsorption is active in the thick ascending limb by NaKATPase generating a gradient for NKCC2
How does K diffuse back into the interstitium from the thick ascending limb? Why is this vital?
-Leaky RomK channels allow K to diffuse out of tubule cells back into the filtrate
-Vital because NKCC2 uses K from the filtrate to function and pump Na into the tubule cell
Which part of the nephron is most sensitive to hypoxia and why?
-Thick ascending limb
-Uses alot of energy to function NKCC2 and NaKATPase
What is significant about solute and water reabsorption in the loop of henle?
-Solute and water reabsorption is separated in the loop
Describe the filtrate at the top of the ascending limb of loop of henle
What is the function of the DCT?
-Fine-tune the filtrate to allow extra absorption of solutes and water
What determines that water permeability of late DCT and CD?
What diuretics target NCCT?
How much Na is reabsorbed in DCT?
Besides from Na, what other main solute is absorbed in DCT? What controls this?
What are the two distinct cell types in the late DCT and CD?
What are the function of principle cells and intercalated cells?
-Principle cells -> Reabsorption of Na via ENaC
-Intercalated cells-> Active Reabsorption of Cl, Secretion of H or HCO3
Describe Na Reabsorption by Principle cells
What effect does this have on Cl reabsorption
-NaKATPase on basolat membrane creates Na gradient
-Concentration gradient for active uptake of ENaC
-No accompanying anion through ENaC so there is a negative charge created in lumen
-Driving force for paracellular Cl uptake
How does ADH influence water permeability in Late DCT and CD?
-ADH increases the expression of AQP2 channels on apical membrane of tubule cells
-AQP channels always present on basolat
-Water moves into interstitium down osmotic gradient
What is pressure natiuresis and diuresis?
-Increased renal artery bp
-Reduced number of NHE and NaKATPase in PCT
-Reduced Na and H2O reabsorption in PCT
-Thus increased Na (natriuesis) and H2O excretion
-ECF volume decreased