Simple cuboidal epithelium is a type of epithelium tissue. Like other types of epithelium, it is a tissue that covers a surface. It consists of only one layer of cube-like cells, which have large, spherical and central nuclei. Simple cuboidal epithelium is found on the surface of ovaries, the lining of nephrons, the walls of the renal tubules, parts of the eye and thyroid, and in salivary glands. On these surfaces, the cells perform secretion and filtration. These cells provide protection and may be active (pumping material in or out of the lumen) or passive, depending on the location and the purpose of the cells.