4 Renal Tubule Function 1 Flashcards
How much of the proximal tubule is convoluted or straight?
60% convoluted
40% straight
What enhances the surface area of the proximal tubules?
microvilli forming a brush border
What facilitates secondary active transport?
ion channels
exchangers
cotransporters
What facilitates primary active transport?
pumps
What is largely responsible for the movement of water?
Na+ movement creating an osmotic gradient
How much water is reabsorbed by the proximal tubule?
by the end of the tubule 70% is reabsorbed
How does sodium move out of the filtrate?
Na+ / K+ ATPase on the basolateral membrane removes the sodium from within the cell, so more can come in out of the filtrate
How does water leave the filtrate?
AQP1, through the paracellular route because of the net outward hydrostatic and osmotic forces
Is insulin reabsorbed in the proximal tubule, and what is its’ concentration like at the end?
No, high
Is Urea reabsorbed in the proximal tubule, and what is its’ concentration like at the end?
Weakly reabsorbed
but its’ concentration is still higher at the end because it is reabsorbed slower than the rate of water
Is chloride reabsorbed in the proximal tubule, and what is its’ concentration like at the end?
Weakly reabsorbed, but its’ concentration is still higher at the end because it is reabsorbed slower than the rate of water
Are Na+ and K+ reabsorbed in the proximal tubule, and what are their concentrations like at the end?
they are reabsorbed, but their concentrations are the same at the end
are carbonate ions reabsorbed in the proximal tubule, and what is the carbonate concentration at the end?
Yes, reabsorbed
Are amino acids and glucose reabsorbed in the proximal tubule, and what are their relative concentrations at the end?
strongly reabsorbed, therefore much lower concentrations
How is glucose reabsorbed in the proximal tubule?
SGLT’s in the apical membrane
GLUT’s in the basolateral membrane
What are the different SGLT’s?
SGLT 2 (low, affinity but high capacity, letting through 1 Na+ at a time but transporting 90% of the NA+)
SGLT 1 (high-affinity / low capacity, letting through 2 Na+ at a time but transporting only 10% of Na+)
what is the distribution of SGLT’s and GLUT’s like?
SGLT 2 and GLUT 2 early tubule
SGLT 1 and GLUT 1 late tubule
what is the significance of tubular maximum transport?
for substances like glucose, which can be filtered out of the blood indefinitely depending on its’ concentration and GFR, if too much is in the blood then it will stay in the filtrate, as only so much can be reabsorbed
Name 2 SGLT2 inhibitors
canaglifozin
dapaglifozin
What are SGLT2 inhibitors used for?
to treat diabetics
What is plasma amino acid concentration?
2.5 - 3.5 mM
What are most amino acid transporters like?
cotransporters of Na+
use the sodium gradient to pull amino acids out of the filtrate
How does HCO3- leave the filtrate?
equilibrium in filtrate to form H2O and CO2, pass over membrane, equilibrates to re-form H+ and HCO3-, HCO3- then leaves the cell
How does HCO3- leave the basolateral membrane of the proximal tubule?
3 HCO3- / Na+ symporter
What facilitates the equilibration of HCO3-?
carbonic anhydrase
What does acetazolamide do?
blocks carbonic anhydrase, acting as a weak diuretic, although it is not used anymore
What would acetazolamide be used for?
glaucoma
mountain sickness prophylaxis
What is one effect of acetazolamide on urine?
makes it more alkaline, leading to metabolic acidosis
How does caffeine lead to diuresis?
antagonist to adenosine (A1) receptor
increases glomerular filtration rate by opposing the vasoconstriction of renal afferent arteriole
inhibits Na+ reabsorption at proximal tubules
water reabsorption is hence inhibited
How does Cl- get absorbed by proximal tubule endothelium from the filtrate?
uses an antiporter for other ions like HCO3- or HCOO-
Why is less Cl- moved than Na+ in the early proximal tubule?
reabsorption of HCO3-
charge difference balanced by Na+ absorption
What happens to Cl- concentration over the proximal tubule and what is the effect of this?
it increases as sodium pulls out water
this drives passive paracellular Cl- movement
How does the proximal tubule reabsorb albumin?
endocytosed by filtrate plasma membrane
catabolised into its amino acids for recycling
Name 3 organic anions actively secreted in the proximal tubule into the filtrate from the blood
penicillin
P-aminohippuric acid
Furosemide
How are organic anions secreted?
basolateral membrane - organic anion transporters (OAT)
luminal membrane - multidrug resistance associated protein (MRP)
