TUBULAR REABSORPTION
Part II
DR .IMRANA EHSAN
Solute and water reabsorption inLoop
of Henley
Reabsorption in the Loop of Henle
Tubular fluid
PCT reabsorbed 65% of the filtered water so chemical
composition of tubular fluid in the loop of Henle is quite
different from plasma since many nutrients were
reabsorbed as well, osmolarity of tubular fluid is close
to that of blood
Sets the stage for independent regulation of both
volume & osmolarity of body fluids.
THIN DESCENDING LIMB: Highly permeable to water
and moderately permeable to solutes.
20% of fluid reabsorbed
Symporters in the Loop of Henle
ASCENDING LIMB :
THIN ASCENDING LIMB:
impermeable to water.
Thick ascending limb: has Na+
K- Cl- symporters on liminal
side that reabsorb these [email protected]
ions
K+ leaks through K+ channels
back into the tubular fluid
leaving the interstitial fluid and
blood with a negative charge
Na/Kpump on basolateral
membrane
Ca, Mg, Na ,K passively move
to the vasa recta BY
PARACELLULAR ROUTE.
DESCENDING LOOP OF HENLE: No
active transport of salt out of the
descending loop of Henle.
ASCENDING LOOP OF HENLE:
Chlorine ions actively transported
out of loop into the interstitial
space. Oppositely charged sodium
ions follow. However, water does
not move out of the ascending
loop.
A concentration gradient IN THE
INTERSTITIAL SPACE has been set
up by the chlorine ( plus sodium)
transport.
Early distal convulated tubule:
• Reabsorption on the early distal convoluted tubule
–
–
–
–
Na+-Cl- symporters reabsorb Na+ and Cl-, Ca,Mg.
Na/K Pump at basolateral membrane
Na Cl cotransport on luminal surface
Major site where parathyroid hormone stimulates reabsorption
of Ca+ depending on body’s needs
• Reabsorption and secretion in the late distal convoluted
tubule and collecting duct
–
–
–
–
90-95% of filtered solutes and fluid have been returned by now
Principal cells reabsorb Na+ and secrete K+
Intercalated cells reabsorb K+ and HCO3- and secrete H+
Amount of water reabsorption and solute reabsorption and
secretion depends on body’s needs
Early distal covulated tubule
DISTAL TUBULE AND CORTICAL
COLLECTING DUCTS
Medullary collecting ducts
Hormonal regulation of tubular
reabsorption and secretion
– Glomerulotubular balance
– Increased tubular load increases reabsorption rates
– Angiotensin II - when blood volume and blood pressure decrease
• Decreases GFR, enhances reabsorption of Na+, Cl- and water in PCT
– Aldosterone - when blood volume and blood pressure decrease
• Stimulates principal cells in collecting duct to reabsorb more Na+ and
Cl- and secrete more K+
– Parathyroid hormone
• Stimulates cells in DCT to reabsorb more Ca2+
• 2nd line of defence
• Prevents overloading of distal tubular segments
Fluid flow in pertubular compartment