Luteal cell, transmission electron micrograph (TEM). Luteal cells occur in the ovarian corpus luteum. Their ultrastructure is typical of steroidogenic cells with mitochondria, dispersed smooth endoplasmic reticulum and lipid inclusions. The sex steroids secreted by luteal cells are progesterone and oestrogen. These steroids act on the uterine lining to prepare it for a potential implantation of a conceptus, and to contribute to modulate pituitary secretion of FSH (follicle stimulating hormone) for inhibition of follicle growth in the ovary. Magnification: x4,000 when width printed at 10cm.