Leydig cell of testis. Coloured Scanning Electron Micrograph (SEM) of endoplasmic reticulum in a Leydig cell of a 14 week human foetus. Leydig cells produce steroids in the male testis. Here, endoplasmic reticulum (ER) membranes fill most of this secretory cell. Smooth ER is yellow; rough ER (green) is dotted with ribosomes involved in protein synthesis. The synthesis of lipids and steroids occurs within the lumen of these paired ER membranes. Lipid droplets are the round orange structures. Mitochondria (pink) produce chemical energy; the cell membrane is coloured blue. Magnification: x8,100 at 6x7cm size. x10,400 at 4x5"~PORTRAIT"