Renal 2. Tubular Reabsorption and Secretion Flashcards
What does the proximal tubule reabsorb / secrete ?
Reabsorbed: Na+,Cl-,K+,Ca+,HCO3,H2O
Glucose, AA, vit.,urea,choline
Secreted:
H+
What does the loop of henle (descending limb) reabsorb / secrete ?
Reabsorb:
H2O ONLY
Secret:
NOTHING
What does the loop of henle (ascending limb) reabsorb / secrete ?
Reabsorb:
Na+, Cl-, K+, Mg,Ca+
Secrete
NOTHING
What does the Distal tubule reabsorb / secrete ?
Reabsobed: Na+, Ca+, Cl-, H2O
Secrete :
K+, H+
What does the collecting duct reabsorb / secrete ?
Reabsorb:
Na+,K+,Cl-,Ca+,HCO3,H+,urea, H2O
Secrete:
H+,H+
Of all the salt that enters the nephron, how much is reabsorbed? And where?
70% will be reabsorbed from the proximal tubule right away. So salt freely filter from the blood into the proximal tubule and then 70% will be reabsorbed back into the blood. The remaining 30% will be processed in different parts like the thick ascending limb (25%) and the remaining 5% will be split between the distal convulated tubule or down in the collecting duct.
What are the two pathways for reabsorption
1) paracellular and transcellular
2) driving forces by transporters (channels)
Which pathway does Na+ use for reabsorption?
Both transcellular transport and Transporters are used for the driving force of transport or Na+ as well a
Explain the driving forces for Na+ transport of reabsorption
Na+ moves from the luminal to basal (blood-side) side. Lumen is (-) and basal is (+)
- Na/K pump on basal side acts as electromotive force that creates the charge separate b/w the sides.
- flow of (+) charge form the basal to lumen via a tight junction (paraceullar)
- Na+ enter lumen via transcellular transport to get to basal side .
- also a backleak of Na+ via tight junction form basal to lumen
What are the stages the transport of Na+ and Cl- go through?
1) Early Proximal Convoluted Tubule
2) Thick Ascending Limb
3) Distal Convoluted Tubule
4) Principle Cell of Connecting Tubule (CNT) or Cortical Collectible Tubule
Transport of Na+/Cl- at the stage of:
1) Early Proximal Convoluted Tubule
1) . Na/K pump —> sets gradient. keeps Na inside cell low by REABSORBING Na from the cell to the interstitial space, also moves K+ inside cell. Pump keeps Na low inside cell so apical Na/Glucose cotransporter works
2) . Na/Glucose cotransporter (S.A.T) —> moves glucose AND Na+ inside cell. Na+ releases E as moves down its gradient. Glucose moving against its gradient = REABSOPTION of glucose
3) Na/H exchanger —-> moves Na+ inside cell, and it secretes H+ ions into the lumen.
4) Paracellular route (Na+/H2O): all Na+ that entered (-) charged lumen is moved back to interstitial space with H2O via tight junction do maintain (-) charge of lumen = maintain gradient.
• how does the secondary active transporter in the early proximal tubule for transporting Na+ and Cl- function??
doesn’t directly use ATP, indirectly uses ATP of the Na/K pump to keep Na low and have electochemical gradient that favours Na movement inside of the cell from the lumen.
For the transport of Na+/Cl-, what’s the charge of the lumen ?
(-) charged
For the transport of Na+/Cl-, how is the Na+ taken to the lumen via [Na+/H+] exchanger ?
Na+ is recycled back to the interstitial space via:
A) Na+/Glucose co transporters
B) paracellular transport Na+/H2O
Transport of Na+/Cl- at the stage of:
2) Thick Ascending Limb
1) Na/K pump: sets up the gradient
2) Na+/H+ exchanger (Apical) brings Na+ inside cell to exit on basal side via Na/K pump to be REABSORBED.
3) Na+/K+/Cl- cotransporter (S.A.T), Indirectly relies on ATP generated on the Na/K pump (on basal side)which reduced Na inside of the cell so Na+ on the lumen side can move down gradient towards the basal side to become REABSORBED.
4) Cl- transporter on basal side to allow for Cl- taken up by the Na+/K+/Cl- cotransporter to pass through the cell and be REABSORBED into the interstitial space.
5) paraceullar transport (lumen is +)
Transport of Na+/Cl- at the stage of:
3) Distal Convoluted Tubule
1) Na/K pump: sets up the gradient
2) Na/Cl co transporter that allows for the REABSOPTION of both ions into the cell and out into the blood. Na+ exits the cell and into the blood via the Na/K pump and Cl- via the Cl- channel on the basal side.
- impermeable to water, but can be made permeable if dehydrated.
In the Thick ascending limb for the transport of Na+ and Cl-, what are the charges of the luminal side, basal side, and inside the cell?
Luminal side = (+)
Basal side (+)
Inside cell = (-)
In the early proximal consulates tubule for the transport of Na+ and Cl-, what are the charges of the luminal side?
Luminal side = (-)
In the distal consulated tubule for the transport of Na+ and Cl-, what are the charges of the luminal side
Luminal side = (-)
Transport of Na+/Cl- at the stage of:
4) Principle Cell of Connecting Tubule (CNT) or Cortical Collectible Tubule
1) Na/K pump: sets up the gradient
2) contains both a Na+ channel , transporting Na+ inside the cell to be REABSORBED, as well as a K+ channel taking K+ out to the lumen
In the principle cell of the connecting tubule, for the transport of Na+ and Cl-, what are the charges of the luminal side
Luminal side = (-)
The Kidney’s High O 2 Consumption Reflects a
High Level of Active Na+ Transport
Two reasons why kidneys need high blood flow at rest:
- Because their doing actions on the blood like filtering, reabsoprtion, secretion
- Cuz of all the Na/K ATPase pumps that require a lot of O2 that generate a lot of ATP to run these pumps
• more oxygen consumed, more ATP made to reabsorb more Na. Linear relation
Before K+ is excreted by the kidneys, what happens to K+?
Ingested K+ Moves Transiently into Cells for Storage Before Excretion by the Kidney
If you have chronically low K+ levels, then it can be
fatal.
A rise in K+ in the plasma will
decrease quickly but gradually.
A rise in K+ in the plasma will decrease quickly but gradually how is this possible?
because K+ can be moved out of the blood and into peripheral cells like muscle cells. Then K+ can sit in those cells and slowly be released into the blood for the time it takes to process it in the kidney (slow).
• So we can store K+ and release it slowly
Which kind of cells is K+ stored in ?
Muscle cells
An increase in plasma K+ =
moved into muscle cell for storage.
An increase in plasma K+ = moved into muscle cell for storage, this is done through 3 ways:
- Insulin can act to move K+ onto the cell, cuz Insulin facilitates GLUT4 transporters to move K+ into the cell. Also activated Na/K ATPase pumps on the muscle cells (move Na out and K in).
- Epinephrine can increase activity of Na/K ATPase pump as well.
- Aldosterone also can activate Na/K ATPase pump on the muscle cells too to move K inside the cell.
Acid-Base Disturbances and K+ Kinetics
- An increase in H+ (decrease pH) = acidodic, so when H+ gets in the cell, it inhibits the Na/K pump, so K+ will stay elevated in the blood.
- H+ block the Na/Cl cotransporter as well in the muscle cells, increasing K+ in the blood even more.
- H+ displace the K+ on the proteins inside of the muscle cell and now the K+ goes down its gradient, out of the cells, elevating K+ plasma levels even more. Deadly
Under a low dietary K+ intake
Low K+ intake - LOW K+ reabsorption in the collecting duct. NONE is secreted.
Under normal K+ intake
you secrete about 20% of K form the CNT, so you have a normal amount of K in your urine.
High intake of K+ = 180% will be secreted. Active K+ secretion to maintain proper blood acid base balance and homeostasis. A lot K+ secretion in the collecting tubule
What are the stages the transport of Na+ and Cl- go through?
1) Proximal tubule
2) Thick ascending limb
3) cortical collecting tubule (CCT)
The transport of K+ at the stage of:
1) Proximal tubule
1) Na/K pump = sets up gradient, allows for REABSOPRTION of Na+ as Na+ is leaving cell and going into blood.
2) K+ channel aboth on apical and basolateral sides.
3) K+/Cl- co transporter on basolateral side that allows for the REABSORPTION of Cl- out of the cell and into blood.
4) paracellular transport of K+/H2O into the blood. most important for K+ REABSORPTION. Causes lumen to go form (-) to (+) charged.
The transport of K+ at the stage of:
2) Thick Ascending limb (TAL)
1) Na/K pump = sets up gradient
2) Na/K/Cl co transporter: (SAT), allows for the REABSOPTION of K+ and Cl+ as there are Na and Cl channel located on the basolateral side, allowing for them to go through the principle cell and into the blood.
3) K+ channel on the apical side which SECRETES K+ on the apical side
4) paraceullar transport of Na+ and K: RETURNS MOST K+ to the basolateral side to be REABSORBED after it was secreted. So very LITTLE SECRETION K+ is occurs here.
The transport of K+ at the stage of:
1) Proximal tubule, what’s the charge of the lumen?
The charge changed form (-) to (+) because of the paracellular transport of K+ ions out of the lumen and into the blood.
This (+) stays until the thick ascending limb.
The transport of K+ at the stage of:
2) Thick Ascending limb (TAL), what’s the charge of the lumen?
It’s still (+) from the proximal tubule after it switches form (-) to (+)
The transport of K+ at the stage of:
3) cortical collecting tubule (CCT)
THIS IS WHERE K+ SECRETION OCCURS.
1) Na/K pump = sets up gradient
2) 2X K+ channels, one for each side. The one on the apical side = SECRETION OF K+ @ normal levels under normal intake of K+.
What are the phases the transport of GLUCOSE has to go through?
1) Early Proximal Tubule (S1)
2) Late Proximal Tubule (S3)
The transport of GLUCOSE at the stage :
1) Early Proximal Tubule (S1)
1) Na/K pump = sets up gradient
2) Na+/GLUCOSE co transport on the apical side that brings glucose inside of the cell. (SGLT2 transporter)
3) Na+/GLUCOSE co transport on the basolateral side that allows for REABSORPTION of glucose into the blood (GLUT2 transporter)
The transport of GLUCOSE at the stage :
2) Late Proximal Tubule (S3)
1) Na/K pump = sets up gradient
2) Na+/GLUCOSE co transport on the apical side that brings glucose inside of the cell. (SGLT1 transporter)
3) Na+/GLUCOSE co transport on the basolateral side that allows for REABSORPTION of glucose into the blood (GLUT1 transporter)
Handling of glucose along the nephron
1) 98% is REABSORBED in the PCT
2) 2% remains, the REABSORPTION for the remaining 2% occurs along the rest of the nephron.
2) 0% of filtered glucose in urin. ALL REABSORBED!!
If you have glucose in the urine, then?
You have diabetes bitch
Glucose titration curve
Once glucose passes the plasma threshold for glucose concentration:
1) Excretion rises exponentially.
2) Reabsorption rises but then platues to a constant level of 400 (transport maximum)
3) Filtered load, doesn’t change, continues to rise at the same rate as before.
The fasting plasma glucose concentration is normally
4 to 5 mM
70 to 100 mg/dL
Where is the Transport maximum found?
This is seen at the point where the filter load goes up ALOT and REABSOPTION platuaqes after it rises with filter load. But filter load continues to rise.
What is transport maximum ?
This is the maximum amount of transport that the kidneys nephrons are able of reabsorbing glucose.
Why does the transport maximum exist?
Limited number of GLUT 1 and GLUT 2 transporters and Na/glucose co transporters.
If you have a pathological condition that downs your transporters then you have
glucose in urine which may indicate diabetes.
