Week 4 - Plasma Volume Flashcards
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?
- NHE
- Na:Glucose
- Na:a’a
Name the transporter of LoH?
-NKCC2
Name the transporter of DCT
-NCC2
Name the transport channel of late DCT and CD
-ENaC
Why is it significant that the tubular cells are polarised?
-Stop transporters from switching membranes
What governs uptake of solutes into peritubular capillaries?
-Concentration gradient
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?
-Ascending
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
-Hypo-osmotic
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?
-ADH
What diuretics target NCCT?
-Thiazide
How much Na is reabsorbed in DCT?
-5-8%
Besides from Na, what other main solute is absorbed in DCT? What controls this?
- Calcium
- PTH
What are the two distinct cell types in the late DCT and CD?
- Principle cells
- Intercalated cells
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
- BP decreases
What is the major osmotically effective molecule in ECF?
-Na
