Transmission electron micrograph (TEM) of the ultrastructure of a columnar epithelium showing four epithelial cell nuclei with their cytoplasm extending from the base to the apical membrane from which stereocilia (modified microvilli) project. Mitochondria are numerous and the basal cytoplasm shows rough endoplasmic reticulum and a rich supply of Golgi membranes is seen more apically together with many cytoplasmic vesicles. These organelles indicate active synthesis of proteins for secretion by the epithelium. This epithelium is from the epididymis. Magnification: x4,000 when height printed at 10cm.