Leydig cell. Coloured transmission electron micrograph (TEM) of part of a Leydig cell from the testis. Leydig cells are involved in steroid synthesis and secretion of testosterone which is essential for spermatogenesis and for maintenance of secondary sexual characteristics such as hair distribution and pitch of voice. Large amounts of agranular enoplasmic reticulum occupies the cytoplasm (yellow) and is characteristic of endocrine cells. Large lipid droplets and mitochondria are also present. Magnification: x15000 when printed at 10 centimetres wide.