Lecture 6-Control Of Volume

Question 1

To change the plasma (ECF) volume, why not just add or remove water to or from the plasma?

Answer 1

Because that would change the plasma osmolarity so an iso-osmotic solution needs to be added to increase the volume

Question 2

Describe the effect of ECF volume in terms of pressure natriuresis and diuresis

Answer 2

When renal artery BP increases, it reduces the number of NHE and Na/K ATPase in the PCT -> reduced sodium and water reabsorption -> increased sodium and water excretion (natriuresis and diuresis) -> ECF volume decreases and initial BP rise diminished

Question 3

What are the Na+ transporters in the PCT?

Answer 3

NHE
SGLT2
Na-AA co-transporter
Na-Pi

Question 4

What are the Na+ transporters in the Loop of Henle?

Answer 4

NKCC2

Question 5

What are the Na+ transporters in the early DCT?

Answer 5

NaCl co-transporter

Question 6

What are the Na+ transporters in the late DCT and CD?

Answer 6

ENaC

Question 7

In S1 of the PCT, why does Cl- reabsorption lag behind?

Answer 7

Because after glucose, AA and lactate are reabsorbed, it used the driving force to reabsorb Cl-

Question 8

Describe the uptake of Na+ and Cl- in the late PCT

Answer 8

Diffusion through tight junctions

Question 9

What % of water does the PCT reabsorb?

Answer 9

65%

Question 10

What is the driving force for water reabsorption in the PCT?

Answer 10

• osmotic gradient by solute reabsorption
• hydrostatic force in interstitium is high
• increased oncotic force in capillary due to loss of 20% of filtrate at glomerulus but protein still in blood

Question 11

Why is the thick ascending limb of the loop of Henle more sensitive to hypoxia?

Answer 11

Uses more energy (needs more ATP) to drive Na/K ATPase for Na+ reabsorption

Question 12

How is Na+ reabsorbed in the early DCT?

Answer 12

Na+ Cl- co-transporter on the apical membrane and Na/K ATPase on basolateral membrane

Question 13

How is Na+ reabsorbed in the late DCT?

Answer 13

Enters via ENaC and leaves via Na/K ATPase

Question 14

How is Ca2+ transported out of the DCT cell?

Answer 14

Through NCX

Question 15

What regulates the transport of Ca2+ through the DCT?

Answer 15

PTH and 1,25-dihydroxyvitamin D

Question 16

What is the collecting duct divided into?

Answer 16

Cortical collecting duct (CCD)

Medullary collecting duct (MCD)

Question 17

Which two types of cells are present in the CCD?

Answer 17

Principle cells and intercalated cells

Question 18

How is Na+ reabsorbed in the principle cells?

Answer 18

In through ENaC and out through Na/K ATPase

Question 19

What are A type intercalated cells?

Answer 19

Secrete acid
In CCD and outer MCD, these cells express H+/ATPase and H+/K+ ATPase on their apical membrane and Cl/HCO3- exchanger on basolateral membrane

Question 20

How is K+ secreted in the TAL of the loop of Henle and why does this occur?

Answer 20

Via ROMK to maintain NKCC2 channel