Ecf Osmolarity Controlled By Na

Question 0

1. Osmolarity - adh system

Answer 0

• 1. na or osmolarity stimulates osmoreceptors
     - also low bp or low vol
• 2. Adh is released
     - increases h2o permeability in the distal tube which causes water retention
• 3. Excess na is excreted
• 4. Dilutes the ECF na to correct the problem

Question 1

Two mechanisms regulate ECF osmolarity

Answer 1

1. Osmoreceptor- adh system

2. Thirst and na osmolarity

Question 2

If ECF is hypoosmotic

Answer 2

Less adh

• lose water
• ecf concentration returns to normal

Question 3

2. Thirst and na osmolarity

Answer 3

• the thirst center is in the hypothalamus near adh cells

1. Increase in the ECF osmolarity or dehydration stimulates the thirst center
2. Drinking threshold decreases when na conc increases by 2mEq/L
3. Decrease in blood volume or bp
   Stimulates baroreceptors and adh release

Question 4

Ang II

Answer 4

Also stimulates the thirst center