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

Question 1

Where is the loop of Henle located?

Answer 1

• In medulla (inner layer) of kidneys

Question 2

What are the two parts of the loop of Henle?

Answer 2

• Descending limb
• Ascending limb

Question 3

What are the roles of the descending and ascending limb in the loop of Henle?

Answer 3

• The limbs control the movement of Na+ ions so water can be reabsorbed back into the blood

Question 4

What are the main stages of the loop of Henle at work?

Answer 4

• Active transport of Na⁺ ions out of top of ascending limb
• Water moves out of descending limb by osmosis
• Na⁺ diffuse out of bottom of ascending limb
• Water moves out of DCT and reabsorbed into blood
• Water moves out of collecting duct by osmosis

Question 5

What happens when Na+ ions are moved out of the ascending limb?

Answer 5

• Near top of ascending limb
• Na+ ions actively transported from filtrate out into medulla
• Ascending limb is impermeable to water
• Water remains in the ascending limb
• Creates low water potential in medulla

Question 6

What happens when water moves out of the descending limb?

Answer 6

• Water moves out of descending limb and into medulla by osmosis
• Descending limb is impermeable to ions
• Glomerular filtrate more concentrated as ions can’t diffuse out
• Water in medulla reabsorbed into blood

Question 7

What happens when Na⁺ ions diffuse out of the ascending limb?

Answer 7

• Near bottom of ascending limb
• Na⁺ ions diffuse out of ascending limb and into medulla
• Lowers water potential of medulla
• Ascending limb impermeable to water so no water exits

Question 8

What happens when water moves out of the DCT?

Answer 8

• Water moves out of DCT by osmosis and reabsorbed into blood

Question 9

What happens when water moves out of the collecting duct?

Answer 9

• High ion concentration in medulla, meaning a low water potential
• Water moves out by collecting duct by osmosis
• Water reabsorbed into blood

Question 10

Describe how the nephron maintains a gradient of sodium ions in the medulla by the loop of Henle and how water is reabsorbed by the distal convoluted tubule and collecting ducts

Answer 10

• Active transport of Na+ ions out of top of ascending limb

• Near top of ascending limb
• Na+ ions actively transported from filtrate out into medulla
• Ascending limb is impermeable to water
• Water remains in the ascending limb
• Creates low water potential in medulla

• Water moves out of descending limb by osmosis

• Water moves out of descending limb and into medulla by osmosis
• Descending limb is impermeable to ions
• Glomerular filtrate more concentrated as ions can’t diffuse out
• Water in medulla reabsorbed into blood

• Na⁺ diffuse out of bottom of ascending limb

• Near bottom of ascending limb
• Na⁺ ions diffuse out of ascending limb and into medulla
• Lowers water potential of medulla
• Ascending limb impermeable to water so no water exits
• Water moves out of DCT and reabsorbed into blood
• Water moves out of collecting duct by osmosis
• High ion concentration in medulla, meaning a low water potential
• Water moves out by collecting duct by osmosis
• Water reabsorbed into blood