Week 4 - Plasma Volume

Question 1

Why must Na excretion be able to change in the kidney?

Answer 1

-In order to maintain Na balance and match ingestion to excretion

Question 2

Why must water and salt be added/removed together?

Answer 2

-If you removed one or the other you would change the osmolarity of plasma so addition/removal needs to be isotonic

Question 3

What effect does osmotic and hydrostatic pressure of the peritubular capillaries have on Na reabsorption in PCT?

Answer 3

• If they are reduced it promotes Na and water reabsorption

- If they are increased it inhibits Na and water reabsorption

Question 4

What are the target cells of aldosterone?

Answer 4

-Principle cells of late DCT and CD

Question 5

What is the connection between Na and Cl reabsorption?

Answer 5

• NaKATPase on basolat geeratea Na gradient

- Na resorption occurs down its gradient with Cl accompanying it to maintain electro-neutrality

Question 6

Name the transporters found in the PCT?

Answer 6

• NHE
• Na:Glucose
• Na:a’a

Question 7

Name the transporter of LoH?

Answer 7

-NKCC2

Question 8

Name the transporter of DCT

Answer 8

-NCC2

Question 9

Name the transport channel of late DCT and CD

Answer 9

-ENaC

Question 10

Why is it significant that the tubular cells are polarised?

Answer 10

-Stop transporters from switching membranes

Question 11

What governs uptake of solutes into peritubular capillaries?

Answer 11

-Concentration gradient

Question 12

What is the difference between S1 of PCT and S2?

Answer 12

-Different apical Na transporters

Question 13

What transporters are involved in S1 of pct?

Answer 13

• NaKATPase and NaHCO3 on basolat

- NHE, Na:glu, Na:a’a and NaPi on apical

Question 14

What happens to the concentration of Cl and Urea in S1? What affect does this have on S2?

Answer 14

• Increases to compensate for loss of glucose

- Creates a conc gradient for chloride reabsorption in S2-3

Question 15

What transporters are involved in S2 of pct?

Answer 15

• NaKATPase on basolat

- NHE, paracellular Cl-, Transcellular Cl-

Question 16

What drives water reabsorption into peritubular capillaries?

Answer 16

• Osmotic gradient caused by solute reabsorption
• Hydrostatic force of interstitium
• Oncotic pressure in peritubular capillary

Question 17

What is glomerulotubular balance?

Answer 17

• 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

Question 18

How is the medulla specialised for H2O reabsorption? What does this achieve?

Answer 18

-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

Question 19

Why is it significant that the filtrate is hyperosmotic at the bottom of the loop of henle?

Answer 19

-Creates a concentration gradient for solutes so they can be pumped out of the ascending limb

Question 20

Which limb in the loop of henle is impermeable to water?

Answer 20

-Ascending

Question 21

Describe Na reabsorption in the ascending limb of loop of henle

Answer 21

• 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

Question 22

How does K diffuse back into the interstitium from the thick ascending limb? Why is this vital?

Answer 22

• 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

Question 23

Which part of the nephron is most sensitive to hypoxia and why?

Answer 23

• Thick ascending limb

- Uses alot of energy to function NKCC2 and NaKATPase

Question 24

What is significant about solute and water reabsorption in the loop of henle?

Answer 24

-Solute and water reabsorption is separated in the loop

Question 25

Describe the filtrate at the top of the ascending limb of loop of henle

Answer 25

-Hypo-osmotic

Question 26

What is the function of the DCT?

Answer 26

-Fine-tune the filtrate to allow extra absorption of solutes and water

Question 27

What determines that water permeability of late DCT and CD?

Answer 27

-ADH

Question 28

What diuretics target NCCT?

Answer 28

-Thiazide

Question 29

How much Na is reabsorbed in DCT?

Answer 29

-5-8%

Question 30

Besides from Na, what other main solute is absorbed in DCT? What controls this?

Answer 30

- Calcium | - PTH

Question 31

What are the two distinct cell types in the late DCT and CD?

Answer 31

- Principle cells | - Intercalated cells

Question 32

What are the function of principle cells and intercalated cells?

Answer 32

- Principle cells -> Reabsorption of Na via ENaC | - Intercalated cells-> Active Reabsorption of Cl, Secretion of H or HCO3

Question 33

Describe Na Reabsorption by Principle cells | What effect does this have on Cl reabsorption

Answer 33

- 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

Question 34

How does ADH influence water permeability in Late DCT and CD?

Answer 34

- 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

Question 35

What is pressure natiuresis and diuresis?

Answer 35

- 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

Question 36

What is the major osmotically effective molecule in ECF?

Answer 36

-Na