Water (Muster) - W3

Question 1

If you have low plasma osmolality, what is your urine osmolality and urine volume?

Answer 1

• LOW urine osmo
• HIGH urine volume

Question 2

IF you have HIGH plasma osmo (from walking in the desert), what is your urine osmo and volume?

Answer 2

• Urine osmo is HIGH
• urine volume is LOW

Question 3

If ADH is present, what does that do to water in the urine?

Answer 3

In the presence of ADH there is less water in the urine. More is being reabsorbed.

Urine osmo is UP but urine volume is DOWN.

Question 4

What are the main stimuli for ADH release?

Answer 4

• Osmolality - can be triggered by change of 1% = most sensitive
• Volume Depletion - need to lose larger amount to trigger same response as 1% change in osmolality.
• pain, nausea, meds (narcotics)

Question 5

What receptors sense osmolality and what do they do?

Answer 5

• sensed by osmoreceptors in the BRAin
• increase thirst
• stimulate supraoptic nuclei to release ADH from neurosecretory cells in posterior pituitary

Question 6

What measures a decrease in volume and what does it do?

Answer 6

• carotid and atrial baroreceptors
• stimulate paraventricular nuclei to release ADH from neurosecretory cells in posterior pituitary

Question 7

How much water reabsorption is variable?

Answer 7

5-24.5%

in the collecting duct.

ADH causes to reabsorb more (excrete less than 1L)

NO ADH - excrete up to 36 L/day.

Question 8

What generates the medullary interstitial osmolality?

Answer 8

• Na/K/2Cl pump that puts NaCL into the interstitum.
  
  • gives you 600 osmo.
• ADH - can add urea so you reach 1200 osmo.

Question 9

WHAT happens with urea in the cortex and early medulla?

Distal medullary space?

Answer 9

• water is reabsorbed so concentration of urea is increasing.
• moves down graident into interstitial space - ADH can increase the amount moving

Question 10

What are the urea transporters?

Answer 10

• UT-1 - found in collecting duct
  
  • always kind of on.
  • increased with urea.
• UT-2 - found in thin ascending limb
  
  • used for recycling.

Question 11

How does ADH increase water reabsorption?

Answer 11

• ADH binds to V2 receptors that insert aquaporins on the luminal side.
• More water is reclaimed.

Question 12

Drug that blocks V2 receptor and forces water diuresis. Approved for heart failure.

Answer 12

Tolvaptan

Question 13

What happens if there are genetic mutations in V2?

Answer 13

• prevents adequate response to ADH and causes WATER LOSS
• Nephrogenic diabetes insipidus - no response to ADH
• May also have acquired diabetes insipidus - can occur w/drugs like lithium and loop diuretics, amyloid, and Sjogren’s syndrome

Question 14

How does lithium induce DI?

Answer 14

• enters cell via ENAC proteins and affects ability to synthesize aquaporin channels. May also produce changes in principle cells of collecting tubules.
• occurs in 30-40% of patients using lithium
• disease can be irreversible
• patients rarely become hypernatremic due to drinking a lot of fluid

Question 15

What drives the fluid into the vasa recta?

Answer 15

• primary gradients
  
  • ​actually superseed Starling’s Forces

Question 16

What can cause SIADH?

Answer 16

• brain lesions
• pulmonary lesions
• ectopic secretions
• Drugs
  
  • carbamazepine
  • vincristine
  • cyclophosphamide
  • haloperidol
  • valproate
  • SSRIs