(7) Renal Transport Mechanism: NaCl and Water Absorptions Along the Nephron (Walker) Flashcards
What are the 5 barriers something must cross to be reabsorbed?
5 distinct barriers
- Leave tubular fluid, cross luminal membrane of tubular cell
- Pass through cytosol from one side of tubular cell to the other
- Cross the basolateral membrane of the tubular cell to enter the interstitial fluid
- Diffuse through the interstitial fluid
- Penetrate the capillary wall to enter the plasma
*This is referred to as TRANS EPITHELIAL TRANSPORT
Where are glucose and a.a. 100% reabsorbed in the nephron?
Proximal convoluted tubule
Describe the Overview of reabsorption in the nephron
The proximal tubule reabsorbs aproximately
__ - __ % of filtered water, Na+, Cl-, K+ and other solutes
65- 70%
The proximal tubule reabsorbs virtually ALL of the ________ and ________ filtered by the glomerulus
Glucose
Amino acids
What is the key element that is responsible for the properties of the proximal tubule?
Na-K ATPase pump
Explain this graph
As you travel further down the proximal tubule, the amount of various solutes changes
Diffusion:
Define
Transcellular
Paracellular
Transcellular = Through the cell membrane
Paracellular = Between cells
Facilitated Diffusion:
Two types?
*Notable fact about FD?
Symport: coupled transport of two or more solutes in the same direction
Antiport: coupled transport of two or more solutes in the opposite direction
*At least one of the solutes is transported AGAINST its electrochemical gradient
Na+/K+ ATPase pump
How many Na out?
How many K in?
3 Na out
2 K in
How much Na+ is filtered and reabsorbed per day?
aprox. 25,000 mEq/day
Describe how the Sodium/Hydrogen exchanger works
More _____ than ______ is reabsorbed in the first half of the proximal tubule, and this causes the ____ concentration in tubular fluid to rise along the length of the proximal tubule
More __water___ than ___Cl-___ is reabsorbed in the first half of the proximal tubule, and this causes the __Cl-__ concentration in tubular fluid to rise along the length of the proximal tubule
Chloride moves
Paracellularly? Intracellularly?
Paracellularly
Paracellular movement is determined by the presence or the absence of….
Tight junctions b/w cells
(they retard water movement)
Where are there a ton of tight junction proteins?
Thick ascending limb
&
Collecting duct
What two aquaporin channels do we care about?
Aquaporin-1 (AQP-1)
Aquaporin-2 (AQP-2)
Where is aquaporin-1 (AQP-1) found?
Proximal tubule
Where is aquaporin-2 (AQP-2) found?
Collecting duct
What two factors determine the water permeability of the renal tubule?
- Presence/absence of tight junctions
- Presence of aquaporin channels
Aquaporin II is regulated by…
ADH
At what point in the renal tubule does it become IMPERMEABLE to water?
Thin ascending limb
The _______ part of the distal tubule is 0% permeable to water
Early
SGLT2
Location?
How much glucose does it reabsorb?
S1/early part of PCT
90%
SGLT1
Location?
How much glucose does it reabsorb?
S3/Distal part of PCT
10%
What is an effective pharmacologic intervention for diabetes?
Inhibit the SGLT2 transporters
This will reduce the amount of glucose being reabsorbed into the bloodstream
Describe the major characteristics of the loop of henle
H2O permeable
Solutes impermeable
Describe the major characteristics of the Thin and Thick Ascending Loop
Permeable to NaCl (35-40 %) is reabsorbed here
IMPERMEABLE to water
Where do your loop diuretics target?
Na-K-2Cl co transporter
on the THICK limb of the ascending limb
Describe the countercurrent multiplier
What type of transporter?
The THICK ASCENDING LIMB has:
The DISTAL TUBULE has:
The THICK ASCENDING LIMB has: Na-K-2Cl transporter
The DISTAL TUBULE has: Na-Cl transporter
The collecting ducts are ________ to water in the absence of ADH
impermeable
Function of aldosterone in the collecting duct?
“Fine-tunes” reabsorption of the remaining Na+
Aldosterone aka
“Salt-retaining hormone”
Goals of aldosterone?
- Acts on thick segment of nephron loop, DCT and cortical portion of collecting duct
- Net effect = body retains NaCl and water
- Urine volume is reduced
- Urine has elevated K+ concentration
Major stimulus, Nephron site of action, effect on transport?
What are the three major classes of diuretics?
Thiazide diuretics
Loop Diuretics (Furosemide)
K+ Sparing Spironolactone
Thiazide Diuretics
Mode of action?
Inhibits the reabsorption of
Na+ and Cl-
In the cortical diluting segment of the DCT
DECREASES BLOOD VOLUME AND PRESSURE
Loop Diuretics (Furosemide)
Mode of action?
Inhibits Na-K-2Cl cotransporter in the thick ascending limb
Decreases reabsorption of Na+, K+ and Cl-
Increased urine output
K+ sparing Spironolactone
Mode of action?
Aldosterone-dependent potassium sparing diuretics
INHIBITS Na+/K+ exchange in the distal tubule and collecting duct
PROMOTES K+ retention and Na+ and water loss
HYPOTTENSIVE effect
