Exam 4 Flashcards Preview

630: Medical Physiology > Exam 4 > Flashcards

Flashcards in Exam 4 Deck (23)
Loading flashcards...
1
Q

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

A
  • 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
2
Q

Of the 3 functions which is the most important?

A

the effect on water permeability

3
Q

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

A

impermeable

4
Q

What happens to the principal cells when ADH is present?

A

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

5
Q

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

A

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

6
Q

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

A

aquaporin 2 (AQP2)

7
Q

Hyperosmotic urine has an osmolarity that is _____ than blood osmolarity

A

higher

8
Q

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

A

high

9
Q

What are the 2 mechanisms by which urine becomes hyperosmotic?

A
  • in the presence of ADH

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

10
Q

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

A
  • countercurrent multiplication

- urea cycling

11
Q

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

A

equal to

12
Q

Hyposmotic urine has an osmolarity that is _____ than blood osmolarity

A

lower

13
Q

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

A

low (or ineffective)

14
Q

How is hyposomotic urine produced?

A

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

15
Q

What does hyposmotic urine osmolarity reflect?

A

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

16
Q

Hyposomotic urine is produced as the normal response to what?

A

drinking water

17
Q

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

A
  • central diabetes insipidus

- nephrogenic diabetes insipidus

18
Q

Central diabetes insipidus follows what?

A

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

19
Q

What does central diabetes insipidus result in?

A

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

20
Q

How is central diabetes insipidus treated?

A

Administration of dDAVP

21
Q

Nephrogenic diabetes insipidus is the result of what?

A

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

22
Q

What does nephrogenic diabetes insipidus result in?

A

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

23
Q

How is neprhogenic diabetes insipidus treated?

A

with thiazide diuretics