Transport Mechanisms in the Nephron

Question 1

What are the [ion]’s of tubule cells comparable to?

Answer 1

Salty Banana

Question 2

What is the [ion] of the filtrate in the lumen?

Answer 2

filtrate derived from the blood has a high [Na]

-Na always wants to leave the filtrate into the tubule cells

Question 3

What is the overall theme of the proximal tubule?

Answer 3

Reabsorb a lot of things and a lot of volume

Question 4

What are the 9 transporters and channels of the proximal tubule?

Answer 4

1. Na/AA symporter
2. Na/Glucose symporter
3. Na/H exchanger
4. Na/K ATPase
5. Water channel (AQI)
6. Water channel (AQI)
7. AA uniporter
8. Glucose uniporter
9. Paracellular- H2O, K, Cl

Question 5

Which transporters/channels are located on the basolateral membrane of proximal tubule?

Answer 5

4. Na/K ATPase
5. Water channel (AQI)
6. AA uniporter
7. Glucose uniporter

Question 6

Which transporters/channels are located on the luminal/apical membrane of proximal tubule?

Answer 6

1. Na/AA symporter
2. Na/Glucose symporter
3. Na/H exchanger
4. Water channel (AQI)

Question 7

Which channels/transporters are regulated by hormones in proximal tubule?

Answer 7

3. Na/H exchanger
4. Na/K ATPase
   - both regulated by Angiotensen II

Question 8

What is Diabetes Mellitus?

Answer 8

When nephrons are incapable of reabsorbing all the glucose it used to be able to filter in the filtrate

Question 9

What are symptoms of Diabetes Mellitus?

Answer 9

Increased urine volume

Presence of Glucose in the urine

Question 10

How is Diabetes Mellitus caused?

Answer 10

Through saturation of the Na/Glucose symporter

Type 1: deficiency of insulin production
Type 2: Decreased cellular response to insulin

Question 11

What is the overall result of Diabetes Mellitus?

Answer 11

More glucose will be filtered into Bowmans Capsule

Question 12

Why would there be more glucose filtered into Bowmans Capsule?

Answer 12

Na/Glucose symporters in the proximal tubule can become saturated.
-If more glucose is present in the filtrate than what the tubule can handle, some glucose is not reabsorbed and excreted

Question 13

What is it called when the glucose in the blood is not

reabsorbed?

Answer 13

Glucosuria

Question 14

What does glucosuria also cause?

Answer 14

Decrease in glucose reabsorption causes a decrease in how much water is also reabsorbed in the proximal tubule.
-since less water is being reabsorbed there is an increase is the amount excreted

Question 15

What is diuresis?

Answer 15

When an increase of urine volume is produced due to and increased level of solute excretion

Question 16

How does decreasing glucose reabsorption affect water reabsorption?

Answer 16

Water will follow glucose hat hasn’t been absorbed and will follow it by osmosis out of the body

Question 17

What is the overall theme of the descending limb?

Answer 17

Mostly Water absorption with minimal Na absorption

Question 18

Since epithelial cells of the descending limb are packed closely together what process can not happen?

Answer 18

Paracellular transport

Question 19

Is there hormonal controls of the descending limb?

Answer 19

No

Question 20

What are the main channels/transporters in the descending limb?

Answer 20

1. Aquaporin I on the luminal membrane
2. Aquaporin I on the basolateral membrane
3. Na Channel on the luminal membrane
4. Na/K ATPase on the basolateral membrane

Question 21

What is the overall theme of the ascending limb?

Answer 21

Reabsorption of ions

Question 22

Is there hormonal regulation of the ascending limb?

Answer 22

No

Question 23

What are the main channel/transporters in the ascending limb?

Answer 23

1. Na channel on the luminal membrane
2. Na/K ATPase on the basolateral membrane
3. Na/Cl/K Symporter on the luminal membrane
4. Cl/K symporter on the basolateral membrane
5. Na paracellular transportation

Question 24

Does reabsorption of water occur in the ascending limb? If Yes/No why?

Answer 24

There is no reabsorption of water because there are no water channels (aquaporin) for the water to leave the luminal space.

Question 25

Is there paracellular transportation in the ascending limb?

Answer 25

Yes, for Na

Question 26

What is the overall theme of the distal convoluted duct?

Answer 26

To reabsorb ions

Question 27

Is there paracellular transportation in the DCD?

Answer 27

No, epithelial cells are tightly packed together

Question 28

What does the DCD reabsorb that the ascending limb doesn’t?

Answer 28

Ca

Question 29

What is Ca absorption regulated by?

Answer 29

Parathyroid Hormone (PTH)

Question 30

What triggers the release of PTH?

Answer 30

When blood Ca levels are lower than expected PTH is released to stimulate Ca conservation
-tells the kidneys to do a better job absorbing Ca

Question 31

What are the differences between the ascending loop and the DCD?

Answer 31

1. DCD has no paracellular transportation (ascending does)
2. DCD reabsorbs Ca, ascending doesn’t
3. DCD is hormonally regulated, ascending is not

Question 32

What is the overall theme of the collecting duct?

Answer 32

The fine tuner

Question 33

What are the 5 channels/transporters in the collecting dict?

Answer 33

1. Aquaporin II on the luminal membrane
2. Aquaporin III&IV on the basolateral membrane
3. Na channel on the luminal membrane
4. K channel on the luminal membrane
5. NA/K ATPase on the basolateral membrane

Question 34

Which transporters/channels are not hormonally regulated in the collecting duct?

Answer 34

2. Aquaporin III&IV

Question 35

What hormone regulates the Aquaporin II channel in the collecting duct?

Answer 35

ADH will change the location of the aquaporin channel.

-if ADH is present there will be high reabsorption of water

Question 36

What hormone regulates Na channel, K channel and Na/K ATPase in the collecting duct?

Answer 36

Aldosterone