Flashcards in Week 4 - Plasma Volume Deck (36)
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1
Why must Na excretion be able to change in the kidney?
-In order to maintain Na balance and match ingestion to excretion
2
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
3
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
4
What are the target cells of aldosterone?
-Principle cells of late DCT and CD
5
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
6
Name the transporters found in the PCT?
-NHE
-Na:Glucose
-Na:a'a
7
Name the transporter of LoH?
-NKCC2
8
Name the transporter of DCT
-NCC2
9
Name the transport channel of late DCT and CD
-ENaC
10
Why is it significant that the tubular cells are polarised?
-Stop transporters from switching membranes
11
What governs uptake of solutes into peritubular capillaries?
-Concentration gradient
12
What is the difference between S1 of PCT and S2?
-Different apical Na transporters
13
What transporters are involved in S1 of pct?
-NaKATPase and NaHCO3 on basolat
-NHE, Na:glu, Na:a'a and NaPi on apical
14
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
15
What transporters are involved in S2 of pct?
-NaKATPase on basolat
-NHE, paracellular Cl-, Transcellular Cl-
16
What drives water reabsorption into peritubular capillaries?
-Osmotic gradient caused by solute reabsorption
-Hydrostatic force of interstitium
-Oncotic pressure in peritubular capillary
17
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
18
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
19
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
20
Which limb in the loop of henle is impermeable to water?
-Ascending
21
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
22
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
23
Which part of the nephron is most sensitive to hypoxia and why?
-Thick ascending limb
-Uses alot of energy to function NKCC2 and NaKATPase
24
What is significant about solute and water reabsorption in the loop of henle?
-Solute and water reabsorption is separated in the loop
25
Describe the filtrate at the top of the ascending limb of loop of henle
-Hypo-osmotic
26
What is the function of the DCT?
-Fine-tune the filtrate to allow extra absorption of solutes and water
27
What determines that water permeability of late DCT and CD?
-ADH
28
What diuretics target NCCT?
-Thiazide
29
How much Na is reabsorbed in DCT?
-5-8%
30
Besides from Na, what other main solute is absorbed in DCT? What controls this?
-Calcium
-PTH
31
What are the two distinct cell types in the late DCT and CD?
-Principle cells
-Intercalated cells
32
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
33
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
34
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
35
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
-BP decreases
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