Sertoli cell. Transmission electron micrograph (TEM) of a section through a Sertoli cell in the epithelium (lining) of a seminiferous tubule of a testis (testicle). The main function of Sertoli cells is to nourish the developing sperm cells through the stages of spermatogenesis (sperm maturation). They are activated by follicle-stimulating hormone (FSH). Here, several elongating spermatids are embedded in deep crypts within the Sertoli cell cytoplasm, an arrangement that facilitates the release of fully developed spermatids during the process of spermiation. Spermatocytes and several round spermatids are also shown. Magnification: x5500, when printed 10 centimetres wide.