Transport Mechanisms in the Nephron Flashcards
What are the [ion]’s of tubule cells comparable to?
Salty Banana
What is the [ion] of the filtrate in the lumen?
filtrate derived from the blood has a high [Na]
-Na always wants to leave the filtrate into the tubule cells
What is the overall theme of the proximal tubule?
Reabsorb a lot of things and a lot of volume
What are the 9 transporters and channels of the proximal tubule?
- Na/AA symporter
- Na/Glucose symporter
- Na/H exchanger
- Na/K ATPase
- Water channel (AQI)
- Water channel (AQI)
- AA uniporter
- Glucose uniporter
- Paracellular- H2O, K, Cl
Which transporters/channels are located on the basolateral membrane of proximal tubule?
- Na/K ATPase
- Water channel (AQI)
- AA uniporter
- Glucose uniporter
Which transporters/channels are located on the luminal/apical membrane of proximal tubule?
- Na/AA symporter
- Na/Glucose symporter
- Na/H exchanger
- Water channel (AQI)
Which channels/transporters are regulated by hormones in proximal tubule?
- Na/H exchanger
- Na/K ATPase
- both regulated by Angiotensen II
What is Diabetes Mellitus?
When nephrons are incapable of reabsorbing all the glucose it used to be able to filter in the filtrate
What are symptoms of Diabetes Mellitus?
Increased urine volume
Presence of Glucose in the urine
How is Diabetes Mellitus caused?
Through saturation of the Na/Glucose symporter
Type 1: deficiency of insulin production
Type 2: Decreased cellular response to insulin
What is the overall result of Diabetes Mellitus?
More glucose will be filtered into Bowmans Capsule
Why would there be more glucose filtered into Bowmans Capsule?
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
What is it called when the glucose in the blood is not
reabsorbed?
Glucosuria
What does glucosuria also cause?
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
What is diuresis?
When an increase of urine volume is produced due to and increased level of solute excretion
How does decreasing glucose reabsorption affect water reabsorption?
Water will follow glucose hat hasn’t been absorbed and will follow it by osmosis out of the body
What is the overall theme of the descending limb?
Mostly Water absorption with minimal Na absorption
Since epithelial cells of the descending limb are packed closely together what process can not happen?
Paracellular transport
Is there hormonal controls of the descending limb?
No
What are the main channels/transporters in the descending limb?
- Aquaporin I on the luminal membrane
- Aquaporin I on the basolateral membrane
- Na Channel on the luminal membrane
- Na/K ATPase on the basolateral membrane
What is the overall theme of the ascending limb?
Reabsorption of ions
Is there hormonal regulation of the ascending limb?
No
What are the main channel/transporters in the ascending limb?
- Na channel on the luminal membrane
- Na/K ATPase on the basolateral membrane
- Na/Cl/K Symporter on the luminal membrane
- Cl/K symporter on the basolateral membrane
- Na paracellular transportation
Does reabsorption of water occur in the ascending limb? If Yes/No why?
There is no reabsorption of water because there are no water channels (aquaporin) for the water to leave the luminal space.
Is there paracellular transportation in the ascending limb?
Yes, for Na
What is the overall theme of the distal convoluted duct?
To reabsorb ions
Is there paracellular transportation in the DCD?
No, epithelial cells are tightly packed together
What does the DCD reabsorb that the ascending limb doesn’t?
Ca
What is Ca absorption regulated by?
Parathyroid Hormone (PTH)
What triggers the release of PTH?
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
What are the differences between the ascending loop and the DCD?
- DCD has no paracellular transportation (ascending does)
- DCD reabsorbs Ca, ascending doesn’t
- DCD is hormonally regulated, ascending is not
What is the overall theme of the collecting duct?
The fine tuner
What are the 5 channels/transporters in the collecting dict?
- Aquaporin II on the luminal membrane
- Aquaporin III&IV on the basolateral membrane
- Na channel on the luminal membrane
- K channel on the luminal membrane
- NA/K ATPase on the basolateral membrane
Which transporters/channels are not hormonally regulated in the collecting duct?
- Aquaporin III&IV
What hormone regulates the Aquaporin II channel in the collecting duct?
ADH will change the location of the aquaporin channel.
-if ADH is present there will be high reabsorption of water
What hormone regulates Na channel, K channel and Na/K ATPase in the collecting duct?
Aldosterone
