Salt And Water Balance

Question 1

What changes stimulate ADH release? What senses these changes?

Answer 1

Increase in osmolarity and decrease in blood volume
Former : osmoreceptors (anterior hypothalamus)
Latter : baroreceptors (aortic arch and carotid sinus)

Question 2

ADH action in basolateral membrane of principle cells of collecting duct

Answer 2

Binds V2 receptors
Gs protein coupled
PKA phosphorylates cytoskeletal elements causing vesicles containing AQP2 to fuse with apical membrane

Question 3

Other than increasing AQP2 expression in principle cells, what else does ADH do? What receptors mediate these actions

Answer 3

Activates urea carriers (UT) in CD (increasing hypertonicity of interstitium of medulla) - V2 receptors

Stimulates NKCC in TALH
Vasoconstricts - especially descending vasa recta preventing wash out of hypertonicity
— both V1 receptors (Gq-coupled, IP3, Ca2+ activating kinase etc.)

Question 4

Cardiovascular sensors of effective circulating volume?

Answer 4

Baroreceptors in carotid sinus and aortic arch
Stretch receptors in atria and pulmonary circulation
Pressure receptors in renal afferent arterioles

Question 5

Renal sensors of effective circulating volume?

Answer 5

Macula densa (senses NaCl, depends on GFR, depends on ECV)

Question 6

Affects on renin release:
1-increased Cl- in macula densa
2-increase A-II
3-Increase ADH
4-Increase SNS
5-Increase PGs
6-Increased pressure

Answer 6

1 - inhibit
2 - inhibit
3 - inhibit
4 - stimulate
5 - stimulate
6 - inhibit

Question 7

A-II effects on adrenal cortex?

Answer 7

Aldosterone release

Question 8

A-II cause vasconstriction on what in kidneys? Effects on peritubular capillaries?

Answer 8

Efferent arteriole, reducing hydrostatic pressure in peritubular capillaries increasing uptake of water from interstitium

Question 9

Effects of A-II on proximal tubule?

Answer 9

A-II receptor Gs coupled, PKA activates Na/H increasing reabsorption

Question 10

How does A-II help in increasing water content of body?

Answer 10

Stimulates ADH releases and increases thirst

Question 11

Mechanism of action of ANP?

Answer 11

Antagonises RAAS by raising cGMP levels causing vasodilation raising GFR but inhibiting reabsorption to increase the fraction of the sodium load that is excreted