Organisms Respond to their Internal and External Environments: Homeostasis - Control of Blood Water Potential, ADH, DCT & Collecting Duct

Question 1

Define the term osmoregulation

Answer 1

• The regulation of the water potential of the blood by the kidney

Question 2

What cells monitor the water potential of the blood?

Answer 2

• Osmoreceptors

Question 3

Where are osmoreceptors located?

Answer 3

• Hypothalamus of the brain

Question 4

Where do osmoreceptors send signals to?

Answer 4

• Posterior pituitary gland

- Also in hypothalamus

Question 5

What does the posterior pituitary gland release?

Answer 5

• Antidiuretic hormone (ADH) into the blood

Question 6

What effect does ADH have on the volume and concentration of urine?

Answer 6

• More ADH, means lower volume of urine

- More ADH, means higher concentration of urine

Question 7

What happens when ADH is released?

Answer 7

• ADH molecules bind to receptors on plasma membranes of cells in DCT and collecting duct
• Aquaporins are inserted into plasma membrane
• DCT and collecting duct more permeable to water
• Water moves out of DCT and collecting duct, into medulla and into blood by osmosis
• Small amount of concentrated urine is produced, less water lost

Question 8

What are aquaporins?

Answer 8

• Channel proteins for water

Question 9

What can lead to dehydration / a low blood water potential?

Answer 9

• Not drinking enough water
• Sweating
• Exercise
• Eating salty food

Question 10

What are the main steps in the ADH osmoregulation stage?

Answer 10

• Blood water potential detected by osmoreceptors
• Posterior pituitary gland stimulated to release more/less ADH
• More/less aquaporins inserted into plasma membranes of DCT and collecting duct
• More/less water reabsorbed into blood by osmosis

Question 11

Explain what happens when blood water potential is too low

Answer 11

• Water content of blood drops, so water potential drops
• Detected by osmoreceptors in hypothalamus
• Water leaves osmoreceptors by osmosis, so cells shrink
• Posterior pituitary gland stimulated to release more ADH into blood
• More ADH means more aquaporins inserted into plasma membranes of DCT and collecting duct
• More water leaves DCT and collecting duct and enters blood by osmosis
• Urine is in lower volume, but at higher concentration

Question 12

What can lead to hydration / high blood water potential?

Answer 12

• Drinking water

- Eating food

Question 13

Explain what happens when blood water potential is too high

Answer 13

• Water content of blood rises, so blood water potential rises
• Detected by osmoreceptors in hypothalamus
• Water enters osmoreceptors by osmosis, so cells swell
• Posterior pituitary gland releases less ADH into blood
• Less aquaporins inserted into plasma membrane of DCT and collecting duct
• Less water enters blood by osmosis
• Large amount of dilute urine produced, more water lost