Control of Plasma Osmolarity

Question 1

Outline the pathway that regulates plasma osmolarity

Answer 1

Sensors = hypothalamic osmoreceptors, activating

1) ADH: kidney, renal water excretion
2) thirst: drinking water behaviour, water intake

Question 2

What are osmoreceptors and where are they located?

Answer 2

Sense changes in osmolarity = signal 2 pathway responses

Hypothalamus – OVLT

Question 3

What causes a release in ADH?

Answer 3

Predominant loss of water = increase of 1% in osmolarity, sensed by osmoreceptors

Question 4

How does blood volume effect the release of ADH?

Answer 4

10% decrease in blood volume = ADH release at osmolarity normally considered too low to release ADH

10% increase in blood volume = ADH first released at higher than normal osmolarity

Question 5

What causes the activation of thirst?

Answer 5

Significant increase in osmolarity or decrease in volume (<10% changes)

Question 6

What is central diabetes insipidus?

Answer 6

Plasma ADH levels low

Cause = commonly damage to hypothalamus or pituitary

Question 7

What is nephrogenic diabetes?

Answer 7

Acquired insensitivity of the kidney to ADH

Question 8

What is SIADH?

Answer 8

Syndrome of inappropriate ADH secretion

Dilutional hyponatremia = due to reabsorbing vast amount of water they don’t need

Question 9

Outline the role of AQP2

Answer 9

Abundant in apical plasma membrane in the collecting duct principal cells sensitive to ADH

No ADH stim, no aquaporin 2 on apical membrane = limited water reuptake in latter DCT = dilute urine

Question 10

Outline the role of AQP3/AQP4

Answer 10

Always present in the basolateral membrane in the collecting duct

Represent potential exit for water entering via AQP2

Question 11

How do we generate a vertical conc gradient in the kidney?

Answer 11

Juxtamedullary nephron = long loop of henle creates the vertical osmotic gradient

Ascending LoH limb = Na leaves creating 200 mOsm gradient between it and the interstitium

Descending LoH limb = water leaves

Everything keep moving around = gradient

Urea = movement from CD to interstitium and diffusion back into LoH

Stratified conc gradient

Question 12

How do we maintain the vertical conc gradient in the kidney?

Answer 12

Flow in vasa recta in opposite direction =

1) water from the descending LoH limb picked up by concentrated ascending limb of vasa recta
2) Na from ascending LoH moves into vasa recta

= counter current multiplier

Question 13

What is the conc in the deepest part of the kidney?

Answer 13

~1200 mOsm

Question 14

Describe the conc of the top of the loop of henle in regards to plasma

Answer 14

Isotonic to plasma