From the glomerulus the filtrate passes into the proximal convoluted tubule. This is called proximal in relation to the glomerulus and convoluted because it is coiled.

The epithelium is cuboidal and the luminal surfaces is lined by numerous microvilli, forming a brush border. These microvilli increase the surface area enormously. This large surface area is indispensable for the uptake of numerous useful substances filtered at the glomerulus such as glucose, amino acids, ions, water and any albumin that has passed through the pores.