Leydig cells. Light micrograph of a section through Leydig cells in a human testis (testicle). Leydig cells are found in the connective tissues between the seminiferous tubules. They synthesise and secrete the steroid hormone testosterone, which is essential for normal spermatogenesis (sperm production), regulation of pituitary hormone secretion, and maintenance of androgen-dependent tissues or organs. Androgen production by Leydig cells is controlled by pituitary luteinising hormone (LH) for which receptors are found on the plasma membrane of the Leydig cells. Structures in the Leydig cell cytoplasm include mitochondria, lipid and smooth endoplasmic reticulum for steroid synthesis. In humans and some primate species, large crystalloids of Reinke also