Osmolality Regulation

Question 1

What hormone controls water regulation?

Answer 1

ADH (vasopressin)

Posterior pituitary hormone with a half life of ten minutes

Question 2

What is the primary control for ADH secretion?

Answer 2

Plasma osmolarity which is detected by osmoreceptors that are found in the anterior hypothalamus.

Question 3

How do the osmoreceptors work in detecting plasma osmolarity?

Answer 3

When plasma osmolarity is raised, water is leached out of the osmoreceptor . This causes neuronal discharge to increase which results in an increase of ADH secretion. The ADH bind to vasopressin receptors which release aquaporins from vesicles that go to the membrane and
increase water permeability. (Vice versa for when osmolarity decreased)

Question 4

What happens at max level of ADH?

Answer 4

Get maximum amount of aquaporin channels so get max reabsorption of water and a small volume of concentrated urine.

Question 5

What happens when there is no ADH?

Answer 5

Get no aquaporin so the water stays in the collecting duct and is excreted

Question 6

How does the ECF volume influence ADH release?

Answer 6

If the ECF is increased then will get a reduced level of ADH.

Question 7

How is ECF volume detected?

Answer 7

Via low and high P receptors.
Low- found in left and right atria
High- found in carotid and aortic arch baroreceptors

Question 8

What will happen to ADH levels during a haemorrhage?

Answer 8

They will increase to conserve ECF volume

Question 9

What are other external factors that affect ADH secretion?

Answer 9

Increased ADH: Pain, emotion, stress, exercise, nicotine, morphine. Following traumatic surgery, inappropriate ADH secretion occurs, need to be careful about monitoring H2O intake.
Reduced ADH: Alcohol

Question 10

What is the cause of diabetes insipidus?

Answer 10

ADH insufficiency or collecting duct not sensitive to ADH

May arise as a genetic defect in the V2 (ADH) receptor or in gene for aquaporins (H2O channels