Exam 4

Question 1

What are the 3 functions ADH has on the renal tubule?

Answer 1

• It increases the water permeability of the principal cells of the late distal tubule and collecting ducts
• It increases the activity of the Na+-K+-2Cl− cotransporter of the thick ascending limb
  
  • this enhances countercurrent multiplication and the size of the corticopapillary osmotic gradient
• It increases urea permeability in the inner medullary collecting ducts
  
  • enhancing urea recycling and the size of the corticopapillary osmotic gradient

Question 2

Of the 3 functions which is the most important?

Answer 2

the effect on water permeability

Question 3

In the absence of ADH, the principal cells are ______ to water

Answer 3

impermeable

Question 4

What happens to the principal cells when ADH is present?

Answer 4

Water channels, or aquaporins, are inserted in the luminal membrane, making them permeable to water

Question 5

Describe the steps involved in the action of ADH on the principal cells

Answer 5

1) ADH binds to V2 receptors in the basolateral membrane
2) this activates adenylyl cyclase which catalyzes the conversion of ATP to cAMP
3) cAMP activates protein kinase A
4) this causes phosphorylation of intracellular structures
5) vesicles containing water channels are shuttled to and inserted into the luminal membrane of the permeability, thus increasing its water permeability

Question 6

What is the specific water channel that is controlled by ADH?

Answer 6

aquaporin 2 (AQP2)

Question 7

Hyperosmotic urine has an osmolarity that is _____ than blood osmolarity

Answer 7

higher

Question 8

Hyperosmotic urine is produced when the circulating levels of ADH are ____.

Answer 8

high

Question 9

What are the 2 mechanisms by which urine becomes hyperosmotic?

Answer 9

• in the presence of ADH

- by equilibration of tubular fluid in the collecting ducts with the high osmolarity of the corticopapilary gradient

Question 10

What are the 2 ways by which the corticopapillary gradient is established?

Answer 10

• countercurrent multiplication

- urea cycling

Question 11

Final urine osmolarity, in the presence of ADH, will be ____ the osmolarity at the bend of the loop of Henle

Answer 11

equal to

Question 12

Hyposmotic urine has an osmolarity that is _____ than blood osmolarity

Answer 12

lower

Question 13

Hyposmotic urine is produced when the circulating levels of ADH are ____.

Answer 13

low (or ineffective)

Question 14

How is hyposomotic urine produced?

Answer 14

The tubular fluid is diluted in the “diluting segments” because NaCl is reabsorbed without water, because there is no ADH present for osmotic equilibrium to occur

Question 15

What does hyposmotic urine osmolarity reflect?

Answer 15

A combination of all of the diluting segments and the remainder of the distal tubule and collecting ducts

Question 16

Hyposomotic urine is produced as the normal response to what?

Answer 16

drinking water

Question 17

What are 2 abnormal conditions in which dilute urine is produced?

Answer 17

• central diabetes insipidus

- nephrogenic diabetes insipidus

Question 18

Central diabetes insipidus follows what?

Answer 18

head injury, in which trauma depletes the posterior pituitary gland of ADH stores

Question 19

What does central diabetes insipidus result in?

Answer 19

Large volumes of very dilute urine is excreted because the entire distal tubule and collecting ducts are impermeable to water in the absence of ADH

Question 20

How is central diabetes insipidus treated?

Answer 20

Administration of dDAVP

Question 21

Nephrogenic diabetes insipidus is the result of what?

Answer 21

A defect of the receptors for ADH in the principal cells, which makes them unresponsive to ADH

Question 22

What does nephrogenic diabetes insipidus result in?

Answer 22

Water cannot be reabsorbed in the later distal tubule and collecting ducts which means large volumes of dilute urine are excreted

Question 23

How is neprhogenic diabetes insipidus treated?

Answer 23

with thiazide diuretics