Lecture 8-Control of Plasma Osmolarity

Question 1

Where are osmoreceptors in the hypothalamus?

Answer 1

OVLT = organum vasculosum of lamina terminalis

Question 2

When is ADH released and where from?

Answer 2

When there is a loss of water, osmoreceptors in the hypothalamus detect it and increase ADH release from posterior pituitary

Question 3

True or false: a small amount of ADH is always produced

Answer 3

TRUE

Question 4

True or false: osmolarity is more important than volume if volume crashes

Answer 4

FALSE - volume more important

Question 5

The kidney can only partially compensate for a loss in water; what is the ultimate compensation?

Answer 5

Drinking water

Question 6

What are some problems with ADH secretion?

Answer 6

• central diabetes insipidus: low plasma ADH due to damage to hypothalamus or pituitary
• nephrogenic diabetes insipidus: acquired insensitivity of the kidney to ADH
• syndrome of inappropriate ADH secretion (SIADH): excessive ADH secreted -> dilutional hyponatraemia

Question 7

Which AQP channels does ADH insert into the kidney?

Answer 7

• AQP2 in apical membrane of CD

- AQP 3 and 4 on basolateral membrane of CD

Question 8

What happens if plasma osmolarity decreases?

Answer 8

No ADH so no AQP2, 3 or 4 so limited water uptake and loss of lots of hypo-osmotic urine (diuresis)

Question 9

What happens if plasma osmolarity increases?

Answer 9

Kidney reabsorbs as much water as possible as ADH inserts AQP2

Question 10

What makes the descending limb of the loop of Henle permeable to water?

Answer 10

AQP1

Question 11

What is the osmolarity at the tip of the loop of Henle?

Answer 11

1200 mOsm/kg

Question 12

What decreases the osmolarity in the ascending limb of the Loop of Henle?

Answer 12

NaCl leaves and water stays

Question 13

Which channel does urea, as an effective osmole, move through?

Answer 13

AQP

Question 14

What gradient is established at each horizontal level of the loop of Henle?

Answer 14

200 mOsm

Question 15

What maintains the concentration gradient established by the counter-current multiplier in the loop of Henle?

Answer 15

Vasa recta, acts as a counter-current exchanger

Question 16

Explain how the vasa recta maintains the concentration gradient in the loop of Henle?

Answer 16

• descending limb of vasa recta runs with ascending limb of LoH. Na+, Cl- and urea diffuse into lumen of vasa recta, osmolarity of blood increases as it reaches the tip of the loop
• ascending limb of vasa recta with descending limb og LoH. water moves into blood due to higher osmolarity