Proximal convoluted tubule (PCT) of nephrons is responsible for most of the reabsorption capacity of the kidneys. Filtered Glucose, amino acids, proteins, albumin, Bicarbonate, sodium, chloride, phosphate, and uric acid are the main ingredients reabsorbed back to the plasma in the PCTs. And importantly PCT is the exclusive site for the absorption of glucose,amino acids, and proteins.
The absorption process through PCTs mostly involves sodium (Na+) gradient-dependent and megalin-/cubilin-mediated endocytic pathways transport systems. The electrochemical gradient of Na+ required for the transportations is produced by the function of the basolateral 3Na+-2K+-ATPase pump. Besides, the pump net function also leads to a negative intracellular potential. This renal sodium regulation is one of the major energy consuming processes in the kidneys and probably accounts for high     overall renal energy demand which is more than ~10% of total body expenditure while kidneys consist only about 1% of body weight.
The powerful electrochemical gradient of Na+ is then utilized for multiple transportation processes as they are synced with the flow of extracellular Na+ to inside the PCT cells.
Glucose absorption is coupled to Na+ by SGLT1 and SGLT2 proteins.
amino acids absorption is mainly mediated by members of the  solute carrier families(SLC).
Phosphate is  absorbed by the NaPi2a, NaPi2c channels.
Bicarbonate absorption consists of a more complicated process; apical Na+-H+ exchanger drives H+ ions out of the cell in exchange for Na+ entrance. The extracellular hydrogen ions combine with filtered bicarbonate ions to form carbonic acid which is then converted into water and carbon dioxide by carbonic anhydrase IV. Co2 diffuses into the proximal tubular cells via aquaporin 1, where is hydroxylated to form bicarbonate by the act of intracellular carbonic anhydrase II. Intracellular HCO3 is co-transported with Na+ at the basolateral -membrane via NBCe1 co-transporter.
Low molecular weight proteins and albumin are essentially absorbed by the Cubilin-Megalin protein complex function.
Vitamin D which is mostly attached to a carrier protein in blood is also filtered with its carrier through nephrons and reabsorbed by megalin function in PCT.
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