The Renal System II (Lecture 11)

Question 1

______ is when water moves from area of low solute concentration to area of high solute concentration.

Answer 1

osmosis

Question 2

True or False: Kidneys compensate for changes in osmolarity of extracellular fluid by regulating water reabsorption

Answer 2

True

Question 3

True or False: Water reabsorption is a active process.

Answer 3

False, passive \

Question 4

&0% of filtered water is reabsorbed in the ______ and then most of the reaming water is reabsorbed with the help of ADH in the ______.

Answer 4

Proximal tubules

Distal tubules

Question 5

True or False: Water reabsorption follows solute reabsorption

Answer 5

True

Question 6

The ______ limb is permeable to water and doesn’t transfer solutes while the ______ is impermeable to water and transfers solutes.

Answer 6

Descending

ascending

Question 7

The osmotic gradient is established by the ______.

Answer 7

Countercurrent multiplier

Question 8

What is the normal osmolarity in the renal tubules?

Answer 8

300 mOsm

Question 9

How does the countercurrent multiplier work

Answer 9

Active transport of solute into medullary interstitial fluid followed by passive transport of water into medullary interstitial fluid. Repeat. Solutes accumulate near bottom of loop of Henle

Question 10

What is the roles of urea in the medullary osmotic gradient?

Answer 10

• Catabolism of proteins
• Nitrogen elimination
• Extremely water soluble

Question 11

What are the three types if urea transporters?

Answer 11

• UT-A present on epithelial cells lining renal tubules
• UT-B present on endothelial cells on descending limb of vasa recta
• UT-C present on proximal tubules

Question 12

Transport of urea through ______ from filtrate to peritubular fluid contributes approximately 40% of the osmolarity of the gradient

Answer 12

UT-A

Question 13

The role of ______ prevents the diffusion of water and solutes from dissipating the medullary osmotic gradient

Answer 13

Vasa recta

Question 14

How does the osmotic gradient work with the vasa recta?

Answer 14

Descending
- water leaves by osmosis, solutes enter diffusion

Ascending
- water moves into plasma in tubule, solutes into interstitial fluid
Osmolarity is higher due to the lack of urea transporters

Question 15

What are the two water channels involved?

Answer 15

• Aquaporin-3: present in basolateral membrane always

* Aquaporin-2: present in apical membrane only when ADH present in blood

Question 16

ADH stimulates the insertion of water channels ______ into ______ membrane

Answer 16

Aquaporin-2, apical

Question 17

True or False: Maximum amount of water reabsorbed depends on length of loop of Henle.

Answer 17

True

Question 18

Why is it necessary for the body to excrete 440mL of water?

Answer 18

eliminate non-reabsorbed solutes

Question 19

What is the pathway for extracellular fluid osmolarity and ADH secretion to interact

Answer 19

Stimulus = increase in osmolarity of extracellular fluid

Osmoreceptors detect, activate neurosecretory cells in hypothalamus

—> ADH secretion (posterior pituitary)

—> water reabsorption (kidneys)

—> decrease excretion

–> conservation of body water