Osmoregulation

Question 1

What is negative feedback?

Answer 1

mechanisms to restore any deviations from normal in a system back to its original state

Question 2

Why is osmoregulation important?

Answer 2

-HYPERTONIC: too much water leaves cells, crenation, chemical reactions etc, cant occur

• HYPOTONIC: water moves into cells, so cells burst, lysis.

Question 3

What is hypertonic?

Answer 3

blood has too low water potential (less water more ions)

Question 4

What is hypotonic?

Answer 4

blood has too high water potential (more water less ions)

Question 5

What might cause blood to be hypertonic?

Answer 5

• lots of ions in food
• not enough water
• sweating

Question 6

What might cause blood to be hypotonic?

Answer 6

• too much water
• not enough ions

Question 7

What detects change in water potential?

Answer 7

osmoreceptors in the hypothalamus

Question 8

Where is ADH produced?

Answer 8

osmoreceptors in the hypothalamus

Question 9

What stimulates MORE ADH to be produced?

Answer 9

water leaves osmoreceptor cells, stimulating ADH to be produced

Question 10

Where is ADH released?

Answer 10

posterior pituitary gland

Question 11

What effect does ADH have?

Answer 11

• increases the permeability of the walls of the distal convoluted tubule and collecting ducts
• so more water is reabsorbed

Question 12

What happens when ADH reaches the kidneys?

Answer 12

• ADH binds to complementary receptors on the cell membranes of epithelial cells of the collecting duct

Question 13

What happens when ADH binds to receptors?

Answer 13

activates phosphorylase enzyme in the cells

Question 14

What does phosphorylase cause to happen?

Answer 14

• vesicles containing aquaporins
• fuse to cell membranes, integrating more aquaporins into the membrane

Question 15

What are aquaporins?

Answer 15

channel proteins that allow water to pass through

Question 16

What is the effect of ADH on the collecting ducts?

Answer 16

• more channel proteins
• membrane is more permeable to water
• water moves into blood by osmosis

Question 17

How does the loop of Henle reabsorb water from glomerular filtrate? (5 points)

Answer 17

• ascending limb, Na+ actively transported out
• ascending limb impermeable to water
• Na+ diffuse in to descending limb
• water moves out of descending limb to the medulla, which has a lower water potential, by osmosis
• longer loop = lower WP in medulla

Question 18

What causes osmoreceptors to release ADH?

Answer 18

• low water potential in the blood
• water moves out by osmosis
• cell shrivels, ADH secreted

Question 19

How does ADH allow water to enter the blood?

Answer 19

• ADH binding causes vesicles containing aquaporins to fuse to the membrane
• water can move into epithelial cells by osmosis
• water then moves into the capillary