6. Control Of Volume

Question 1

What does a change in Na+ ion concentration in the extracellular fluid result in?

Answer 1

Affects the effective circulating volume, effecting BP.

Question 2

How is Na consumed in the diet?

Answer 2

Salt.

Question 3

Why do you need to add isosmotic solution to increase ECF?

Answer 3

So that plasma osmolarity doesn’t change.

Question 4

Where in the nephron is the most Na+ absorbed?

Answer 4

Proximal convoluted tubule and thick ascending limb of the loop of Henle.

Question 5

Where is the most water reabsorbed in the nephron (and so the most aquaporins are found here)?

Answer 5

Proximal convoluted tubule and collecting duct.

Question 6

What 3 factors alter proximal convoluted tubule Na+ reabsorption?

Answer 6

Changes in osmotic pressure.
Changes in hydrostatic pressure.
RAAS.

Question 7

What is pressure natriuresis?

Answer 7

Increased renal artery BP leading to increased sodium excretion.

Question 8

What is pressure diuresis?

Answer 8

Increased renal artery BP leading to increased water excretion.

Question 9

How is Na+ reabsorption altered when renal artery BP increases?

Answer 9

Reduction in the number of Na-H antiporters and reduction in Na-K ATPase activity in the proximal tubule.

Question 10

What aquaporins are found in the proximal convoluted tubule?

Answer 10

AQP1.

AQP7.

Question 11

What aquaporins are found in the collecting duct?

Answer 11

AQP2.
AQP3.
AQP4.

Question 12

How is chloride reabsorbed from the nephron?

Answer 12

Transcellular (active) and some paracellular (passive) reabsorption. Couples to 3Na-2K-ATPase pumps. So when talk about Na+ reabsorption, Cl- is implied.

Question 13

In which area of the proximal convoluted tubule are Na+ and Cl- mainly reabsorbed?

Answer 13

S2 and S3.

Question 14

What 3 forces drive water reabsorption in the PCT?

Answer 14

Osmotic gradient established by solute absorption (increased osmolarity in interstitial spaces).
Increased hydrostatic force in interstitium.
Increased oncotic force in the peritubular capillary.

Question 15

What part of the nephron is impermeable to water?

Answer 15

Thick ascending limb of the loop of Henle.

Question 16

What is the purpose of water reabosprtion in the descending limb of the loop of Henle?

Answer 16

Concentration of Na+ and Cl- in the lumen of the descending limb, ready for active transport in the ascending limb.

Question 17

Is Na+ reabsorption active or passive in the thin ascending limb of the loop of Henle?

Answer 17

Passive.

Question 18

Which region of the nephron is particularly sensitive to hypoxia and why?

Answer 18

Thick ascending limb of the loop of Henle, as it uses lots of active transport channels to move Na+, K+ and Cl-, so is very metabolically active.

Question 19

What part of the nephron is known as the diluting segment and why?

Answer 19

Ascending limb of the loop of Henle, as absorbs NaCl but not water.

Question 20

In the late distal convoluted tubule and collecting duct, water permeability is variable depending on what hormone?

Answer 20

ADH.

Question 21

What are the two regions of the DCT called?

Answer 21

DCT 1 (early).
DCT 2 (late).

Question 22

What area of the nephron is a major site for calcium reabsorption?

Answer 22

Distal convoluted tubule.

Question 23

Describe the reabsorption of calcium once it has entered a DCT cell.

Answer 23

Cytosolic calcium immediately binds to cal Indian, shuttles calcium to the basolateral aspect of the DCT cell. Transported out of the cell into the blood across the basolateral membrane by sodium calcium exchanger (NCX).

Question 24

What 2 hormones tightly regulate calcium reabsorption in the nephron?

Answer 24

Parathyroid hormone.

1,25-dihydroxyvitamin D (calcitriol).

Question 25

What are the two cell types found in the cortical portion of the collecting duct? What ions do they reabsorb?

Answer 25

Principle cells - Na+.
Intercalated cells (acid and bicarbonate secreting types) - Cl-.