Tubular Transport PCT Transport • Driven by basolateral Na+/K+ ATPase  Na-linked absorption of: o Glucose o Amino acids o Phosphate • Na-linked excretion of: o H+ • Leaky intercellular junctions allow for paracellular water transport in equal amounts to paracellular solute transport • Fanconi Syndrome: syndrome where there is inadequate reabsorption in the PCT due to a range of underlying congenital or acquired conditions o Glucosuria o Amino-aciduria o Impaired acid excretion  acid accumulation in blood (Type 2 (proximal) renal tubular acidosis) Loop of Henle • Majority of solute reabsorption is in TAL o 20-25% of filtered Na reabsorbed o Impermeable to water TAL Transport • Electrochemical gradient driven by Na+/K+ ATPase • Na+/K+/2Cl- cotransporter on luminal surface Paracellular diffusion of Na, K, Ca and Mg Impermeable to water  net dilution of tubular fluid • • DCT Transport • Major site of urine dilution (water mostly can’t follow solutes out) • Solutes are absorbed more than water (DCT water impermeable) • Electrochemical gradient driven by Na+/K+ ATPase • Luminal Na+/Cl-