tubular reabsorption: - selective process that reclaims most of filtrate formed during glomerular filtration- commence as soon as filtrate enters proximal tubule - entire renal tubule involved - solutes move through cells of tubular epithelium and capillary endothelium back into blood of peritubular capillaries - substance reclaimed: water, glucose, amino, electrolytes - proximal tubule cells carry out most reabsorption - Na+ ion most abundant in filtrate. Active transport -> require large ATP.- energy from transporting Na+ facilitates secondary active transport which reabsorb gluc., amino, some ions and Vit. : usually all glu. and amino. absorbed before nephron loop. - concentration gradient: movement of ions - aqauporins in proximal tubule = obligatory water reabsorption nephron loop important for formation of conc. urine - reabsor. of solutes active & passive. - aqauporins vast in descending limb, scarce in ascending limb of nephron loop. - most filtered H20 and solutes reabsp. before distal tubule.
SUMMARY: proximal tubule: site of most reabsorption nephron loop: reabsorption of water & solutes. not coupled. distal tubule and collecting duct : reabsorption regulated by hormones (ADH, Aldosterone, ANP)