Control of Plasma Volume

Question 1

What is the major effective solute in ECF?

Answer 1

Na

Therefore water in ECF depends on Na content

Question 2

When we talk about the movement of sodium what do we infer moves with it?

Answer 2

Cl-

Question 3

How is sodium lost?

Answer 3

Sweat

faeces

Urine

Question 4

Where does the biggest movement of Na take place?

Answer 4

PCT 67%

Question 5

Briefly outline Na % movement in the nephron

Answer 5

PCT = 67%

Ascending limb = 25%

DCT = 5% (variable)

Collecting duct = 3%

Question 6

Outline pressure natriuresis/diuresis

Answer 6

If hydrostatic pressure in the capillaries is high = loose Na

Thus = reduced number of Na-H antiporters and NA/K ATPase = keep reabsorption at 67%

Question 7

Define reabsorption

Answer 7

From the lumen to the capillary

Paracellular = between cell lining tubule

Transcellular = though nephron cell

Mainly driven by the gradient from Na/K ATPase

Question 8

What are aquaporins?

Answer 8

Port for water to move down conc gradient

Present in = PCT, descending limb, collecting duct

Not present = ascending limb

Question 9

Outline the PCT characteristics

Answer 9

Brush border

Large diameter

Lots of mitochondria

Na reabsorption stim by RAAS

Question 10

Discuss PCTs handling of solute/solvent

Answer 10

S1 = fast preferential reabsorption of glucose, AA, phosphate, lactate = 100% reabsorbed, HCO3

S2/3 = Large [Cl] = passive paracellular down conc gradient into capillary

Process of water moving with factors above = reabsorb isosmotic volume, but piece at a time

Question 11

What does bulk uptake refer to?

Answer 11

Very fast isosmotic reabsorption in the PCT

Question 12

Discuss the descending limbs handling of solute/solvent

Answer 12

Aquaporins present = concentrate filtrate by removing water

Thin cells with loose junctions = permeable = subject to conc gradient in interstitium = draw water out of the filtrate

Question 13

Discuss the ascending limbs handling of solute/solvent

Answer 13

Thin seg = water reabsorption creates gradient for passive paracellular Na reabsorption

Thick seg = active transporters removes solute, K secreted, +ve luminal charge allows pick up Ca/Mg, very susceptible hypoxia = as uses lots of energy

NO aquaporins

Question 14

How does the conc gradient change as we move from the cortex to the medulla?

Answer 14

Cortex to the medullar = increase of conc gradient of interstitium

Cortex = isosmotic to plasma

Medullar = VERY concentrated

Use gradient to assist with reabsorption of water in loop of Henle

Question 15

Discuss the DCTs handling of solute/solvent

Answer 15

Region of choice

Hypo osmotic fluid

5-8% Na reabsorption

ENaC (ep Na channel) = sensitive to diuretics

Site for Ca reabsorption = sensitive to PTH

Site of target for aldosterone

Question 16

Discuss the collecting ducts handling of solute/solvent

Answer 16

Runs all the way through the kidney = all the way down the conc gradient

Principle cells = reabsorb Na via ENaC

Intercalated cells = reabsorb Cl, type A secrete H, type B secrete HCO3