Renal Transport Mechanisims Flashcards
What are the two types of transport and define them
Trans-epithelial transport - through the membrane
Paraepithelial transport - through the TJ
What does the PCT absorb most
Glucose 100% AA 100% Urea 50% Na 70% K 70% Phosphate 70% Ca 70%
H2O 70%
What does the PST absorb most
Phsophate
What does the TDLoH absorb
WATER
What does the ThALoH absorb
SOLUTES ONLY!
Na
K
Ca
Mg
What does the DCT and CD absorb
Fine tunes the urine, can absorb or not absorb water or solutes
Where is most of the water REBS in the nephron
In the PCT
What pump powers the REBS of the Na in the PCT
The Na/K Pump
Define symporter
Facilitated transport of two or more solutes in the same direction
Define antiporter
Movement of two solutes in opposite directions
Pushes one down its gradient and one up its gradient with the use of ATP
What does the Na/K Pump create within the cell
A low intracellular Na concentration, thus allowing for Na to move down its gradient
A negative apical side charge which attracts the Na to it
transcellular route Transport across the basolateral membrane involves what and why
The lateral intracellular spaces which receive ions as well as the IF
How does water move in the PCT through the cells
Through the TJ
Na REBS is almost always an active transport where
The transcellular route
While the NHE3 moves Na with active transport, how does Na enter the cells with passive transport, and why
Enters via Na leak channels
Using the same reasons as the NHE3, low intracellular Na bc of Na/K Pump
With the Na being transported into the cell, what else will come with it
Water
How does the water and Na enter the peritubular capillary
Via ultrafiltration, a passive process driven by hydrostatic and colloid osmotic pressure
What is the Antiporter used in the PCT to move Na in and H out
NHE3
Most of the Na that enter the tubule cells does so how
Via NHE3
How does the newly made HCO3 in the cells enter the IF to be taken to the peritubular capillaries
Via a NaHCO3 Co-Transporter
How does the Cl concentration behave within the tubule and what does this mean physiologically
Rises as it proceeds which, along with less water and Na from the proximal PCT, allows Cl to freely diffuse across the apical membrane into the cell of the distal PCT.
What is the major mechanism for chloride REBS
Paracellular movement
What does the presences of TJ’s do in regards to water REBS
Prevents water REBS
So where, would you find excessive TJ’s and little or no AQPs (no water permeability)
ThALoH and the CD
What do AQPs do
Utilize the transcellular movement of water and allows it pass easier
Where is AQP - 1 found
Int he PCT
Where is AQP - 2 found
In the CD
What is AQP - 2 under the control of
ADH
While the PCT has many TJ, it also has what which allows it top be permeable to water
AQP - 1
All water REBS is what
Passive
Glucose is REBS via what type of transport
Active
Define SGLT1
Where is it located, what is its physiological status, and what GLUT does it go with
Is a high affinity, low capacity transport protein that is found in the distal PCT S3 region on the apical side
Because it is high affinity, is used to pick up what glucose is left behind from SGLT2 in the proximal PCT, which means it can operate at low concentrations
Is paired with GLUT1on the basolateral membrane side
Define SGLT2 and it’s physiological status
Is found in the S1 and S2 parts of the PCT.
Is a low affinity, high capacity transporter which allows the proximal PCT to REBS most of the glucose
Links the movement of Na down its concentration gradient with the uphill REBS of glucose, even when glucose concentration inside the cell is higher than tubular fluid concentration
Is paired with GLUT2
What happens if the SGLTs reach their Tm
No more Glucose can be REBS, thus the patient has way too much Glucose in their blood and this is indicated by the presence of Glucose in their urine
What does the TDLoH REBS and what does this mean physiologically
REBS WATER
NOT SOLUTES
This means as the TF moves along, it becomes more concentrated until reaching the ThALoH
This movement of water is caused by the increased osmol. Of the If from the REBS of solute from the ThALoH
The TALoH and ThALoH REBS what and not what and what is the physiological consequence of this
REBS 40% of Na and Cl
NOT WATER
This means the TF becomes much less concentrated as it approaches the DCT because the solutes are being REBS
Is Na REBS linked to other solutes within the ALoH?
No
Define the NKCC2 transporter and why it acts the way it does
Is a symporter which moves 1 Na, 1 K, and 2 Cl into the cell from the apical side
Is able to do this bc of the gradient est. but the Na/K pump
Due to the Na/K pump moving Na out of the cell, what is made on the apical membrane and what does this allow for
A (-) charge is made which allows for the movement of Na, Ca, and Mg via paracellular REBS
Define the NCC transporter and what it does physiologically
Is a Na/Cl co transporter in the DCT which REBS NaCl when told to do so by Aldosterone
How does Thiazide work
Inhibits the REBS of Na and Cl in the DCT by acting on the NCC and inhibiting it, thus allowing for more NaCl in the TF and more water concequently
It also increases Ca REBS which helps to treat Ca kidney stones
How do Loop Diuretics work
Inhibits the NKCC2 transporter in the THALoH which causes a decreased REBS of Na, K, and Cl and also diuresis
How do K + Sparing Spironolactone work
Inhibits Na/K echange in the DCT and CD which promotes K retention, Na retention, and water loss
