Glomerular filtration, tubularReabsorption and tubular Secretion
Glomerular Filtration
180L/day
125ml/min
GFR = Kf x Net filtration pressure (NFP)
(NFP) = (PGC – PBS) – (OnGC - OnBS)
Kf (filtration coefficient) depends on • the hydraulic conductivity (permeability) of the capillary and • the
effective surface area available for filtration.
GFR is directly related to blood pressure
sympathetic stim DECREASE GFR
not a selective process
Tubular Reabsorption
All except potassium
Na+-K- pump and carrier proteins (e.g. glucose transporter or GLUT) always reside on the basolateral
membrane.
Na+ channels and co-transporter proteins (e.g. Na+-glucose symporter, Na+- amino acid symporter, Na+-Cl-
symporter, and Na+-H+ antiporter) are on the apical membrane.
diffusion
Na+, K+, Cl-, urea in the PCT
Morphology of epithelial cells lining various sections of the
nephron
Reabsorption in the Loop of Henle
descending
water ONLY
ascending
Electrolytes
Reabsorption in the early Distal Convoluted Tubule
(DCT)
Ca2+
passive transport
Reabsorption and Secretion in the Collecting Duct
Principal cells reabsorb Na+ and secrete
K+
target for aldosterone and ADH
intercalated cells reabsorb K+ and HCO3-, and secrete
H+
tubular secretion
PCT
H+: variable (via Na+-H+ antiporters)
NH4+: variable, increase in acidosis (antiporters)
Urea: variable (diffusion)
Creatinine: small amount
thin LoH
Urea: variable (recycling from collecting duct)
NH4+: variable (recycling from thick ascending loop of Henle)
CD
K+: variable amount to adjust to dietary intake (via leakage channels of the principle cells)
H+: variable amount to maintain acid-base homeostasis (via proton pump)