Osmoregulation

Question 1

Where is ADH synthesised?

Answer 1

in the hypothalamus

Question 2

Where is ADH released?

Answer 2

in the terminals of the hypothalamic neurones found within the posterior pituitary

Question 3

How does ADH work?

Answer 3

acts in the distal tubule and collecting duct to increase the water permeability by increasing AQP2

Question 4

How does ADH affect AQP2?

Answer 4

increases the number of AQP2 channels, increasing reabsorption

Question 5

Before the number of AQP2 channels are increased, where are they stored?

Answer 5

in vesicles inside the epithelial cell (can be quickly inserted into the membrane (quicker mechanism as synthesis not requires))

Question 6

Why does the osmolality stay the same along the proximal tubule?

Answer 6

even though salt is being reabsorbed so is water so they balance each other out

Question 7

In terms of urine, what does low osmolality result in?

Answer 7

dilute urine

Question 8

When is urea production low?

Answer 8

in the presence of selective protein starvation production is low so that the kidney has a lower capacity to concentrate urine

Question 9

What is the urea transporter and what is it regulated by?

Answer 9

UT-A1
regulated by ADH
When ADH is high, urea absorption is increased, this increases the amount of urea in the extracellular space, increasing water reabsorption

Question 10

What is the role of urea in the renal medulla?

Answer 10

role in maintaining osmolality

Question 11

What is osmolality?

Answer 11

defined as the number of osmoles (Osm) of solute per kilogram of solvent

Question 12

How are the cells of the medulla adapted to survive 1200mOsm? (high osmolality)

Answer 12

to prevent cell swelling, they have to have a high intercellular osmolality. They do this by accumulating a range of organic osmolytes inside the cells. These include: sorbitol, inoitol, glycerophosphorylcholine and betaine

Question 13

Why does diabetes inspidus?

Answer 13

• due to a loss of ADH secretion (central diabtetes inspidus) or a loss in the sensitivity of the kidney to ADH (usually due to a problem in the V2 receptors) (nephrogenic diabetes insipidus)
• unable to produce concentrated urine

Question 14

What does diabetes insipidus lead to?

Answer 14

polyuria
dehydration
hypovolaemia
can also cause people to drink too much

Question 15

How is central diabetes insipidus treated?

Answer 15

uses desmopression (ADH analogue)

Question 16

How is nephrogenic diabetes insipidus treated?

Answer 16

-low salt diet (prevents high sodium conc)

Question 17

How is nephrogenic diabetes insipidus caused?

Answer 17

• toxicity
• hypercalceamia
• genetic due to mutations in either V2 or AQP2

Question 18

What is SIADH?

Answer 18

syndrome of inappropriate ADH (inappropriately high ADH)

Question 19

What is the urine like of someone with SIADH?

Answer 19

v conc

Question 20

How do you treat SIADH?

Answer 20

• fluid restriction
• give urea
• V2 receptor antagonist

Question 21

What happens when there is inadequate water intake?

Answer 21

• increase in osmolality in the plasma
• osmolality is detected in the anteroventral third ventrical (AV3V) region
• AV3V neurones project to the median preoptic area of the hypothalamus which increases thirst

Question 22

What is the max urine osmolality?

Answer 22

1400mOsm

Question 23

Can any animals drink sea water?

Answer 23

yes, in rats urine concs can reach 3000mOsm (so can some other animals)

Question 24

What are the dominant osmolytes in the circulation?

Answer 24

Na+ and Cl- (but aren’t dominat osmolytes ingested e.g carbs, fats and proteins)

Question 25

When can glucuse conc get so high that it contributes to osmolality?

Answer 25

diabetes mellitus