Ch. 9.2. Thirst

Question 1

If you lacked vasopressin, would you drink like a beaver or like
a gerbil? Why?

Answer 1

If you lacked vasopressin, you would have to drink more like a beaver. You would excrete much fluid, so you would need to drink an equal amount to replace it.

Question 2

Would adding salt to the body’s extracellular fluids increase or decrease osmotic thirst?

Answer 2

Adding salt to the extracellular fluids would increase osmotic thirst because it would draw water from the cells into the extracellular spaces

Question 3

Why are you likely to feel thirst just before bedtime? Would you feel just as thirsty if you went to sleep at an unusual time?

Answer 3

At bedtime, your body secretes vasopressin, which helps conserve water and also stimulates thirst. Both responses help you get through the night while you cannot drink. Your circadian rhythm trig- gers the increased vasopressin, so you would not feel as thirsty before going to sleep at an unusual time.

Question 4

Who would drink more pure water—someone with osmotic thirst or someone with hypovolemic thirst?

Answer 4

Someone with osmotic thirst would drink more water. Someone with hypovolemic thirst would drink more of a solution containing salts.

Question 5

What are the contributions of angiotensin II and aldosterone?

Answer 5

Angiotensin II constricts the blood vessels, and stimulates neurons that produce hypovolemic thirst.

Aldosterone causes the body to retain salt at times when blood volume is small.

Question 6

What does vasopressin do?

Answer 6

It decreases urination and increases thirst.