3.2. Regulation of Osmolarity - Plasma Osmolarity

Question 1

What is normal plasma osmolarity?

Answer 1

280-290mOsmoles/Kg H2O = 280-290mOsmoles/L

Question 2

What happens in the Osmoreceptors of the Hypothalamus, if there is an increase in the effective osmotic pressure in the plasma?

Answer 2

1. H2O leaks out of cells
2. The cells shrink
3. Stretch sensitive ion channels are activated
4. This causes an increase in neural discharge (from the Hypothalamus)
5. This causes an increase in ADH (Vasopressin) secretion (from the Posterior Pituitary Gland)

Question 3

What happens in the Osmoreceptors of the Hypothalamus, if there is a decrease in the effective osmotic pressure in the plasma?

Answer 3

1. H2O enters into the cell
2. The cells swell
3. There is a decrease in neural discharge (from the Hypothalamus)
4. This decreases ADH (Vasopressin) secretion (from the Posterior Pituitary Gland)

Question 4

What is effective osmotic pressure?

Answer 4

An increase in Osmolarity which does not cause an increase in tonicity.

Question 5

1. Is effective osmotic pressure effective at causing an increase in ADH (Vasopressin) concentration?
2. What is an example of this?

Answer 5

1. No

2. Urea

Question 6

What do small changes in either direction of tonicity result in?

Answer 6

A rapid change in ADH concentration