Regulation of body fluids

Question 1

What percentage of body water is in the ICF?

Answer 1

2/3

Question 2

What percentage of the ECF is interstitial fluid?

Answer 2

75%

Question 3

What percentage of the ECF is plasma volume?

Answer 3

25%

Question 4

Why do elevated plasma urea concentrations not elicit ADH release?

Answer 4

Cell membrane is impermeable to urea

Question 5

How does plasma osmolality and baroreceptor signaling control the release of ADH?

Answer 5

1. ADH is released from posterior pituitary in response to increased osmolality, causing shrinking of the hypothalamic osmoreceptors 2. ADH is released in response to decreased arterial pressure and/or decreased blood volume

Question 6

How do plasma osmolality and baroreceptor signaling affect thirst?

Answer 6

Thirst is caused by shrinkage of thirst osmoreceptors in response to increased osmolality of ECF

Question 7

What are the effects of ADH on the kidney?

Answer 7

1. Binds vasopressin-2 receptors on collecting ducts - insertion of aquaporins 2. Vasoconstrict pericytes surrounding vasa recta - decreaese blood flow and preserves gradient needed to produce concentrated urine 3. Increases permeability of medullary collecting ducts to urea via increased uniporters 4. Prolonged stimulation