luteum

The corpus luteum, Latin for yellow body, is a temporary endocrine structure in the ovary that forms after ovulation from the collapsed follicle. Following ovulation, granulosa and theca interna cells undergo luteinization, producing a richly vascularized mass of luteal cells.

The primary product of the corpus luteum is progesterone, with smaller amounts of estrogen and inhibin. Progesterone supports the endometrium, promoting secretory changes and maintaining an environment suitable for implantation and early pregnancy. In most humans, the corpus luteum remains functional for about 14 days in a nonpregnant cycle.

If fertilization occurs, human chorionic gonadotropin (hCG) from the embryo rescues the corpus luteum, enabling continued progesterone production and delaying luteolysis until the placenta takes over steroidogenesis, typically during the first trimester.

If pregnancy does not occur, the corpus luteum regresses through luteolysis, becoming fibrous tissue known as the corpus albicans. Hormonal support declines as luteinizing hormone levels fall, leading to menstruation.

Two main cell types compose the corpus luteum: luteinized granulosa cells and theca lutein cells. The granulosa-derived cells originate from the follicle’s granulosa layer, while theca-derived cells come from the theca interna; together they synthesize progesterone under gonadotropic control, primarily that of LH.

In some species and physiological contexts, the timing and regulation of luteolysis differ, and prostaglandins such as prostaglandin F2 alpha can influence the regression process. The corpus luteum thus plays a key role in coordinating the luteal phase of the menstrual cycle and the early stages of pregnancy.