Structure, function, and regulation of the corpus luteum

The corpus luteum-an endocrine gland in the adult ovary-is formed from the follicle wall after ovulation. It is associated with four unique features. The first is its ephemeral nature: the corpus luteum exists for a limited life span that in many species depends on the fate of the oocyte released by the antecedent ovulatory follicle. Second, its primary, if not sole essential function is to synthesize and secrete the steroid hormone, progesterone that acts in the reproductive tract to permit implantation of the early embryo in the uterine endometrium and support a maternal environment that sustains intrauterine pregnancy. Thus, the third feature of the corpus luteum is its physiological connection to viviparity. All mammals, many reptiles, and a few fishes that produce live young exhibit corpora lutea, although the essential connection between the corpus luteum and viviparity is less obvious in nonmammalian species. In some of these species, luteal function may be related to final oocyte maturation, egg movement in the oviduct, or oviposition, because the corpus luteum exists in some oviparous reptiles, amphibians, and birds as well.