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corpus luteum[′kȯr·pəs ′lüd·ē·əm]
in mammals and man, an endocrine gland that develops in the ovary at the site of the graafian follicle after rupture of the follicle wall and discharge of the ovum (ovulation); it consists of altered follicular (so-called lutein) cells. If pregnancy does not follow ovulation, the corpus luteum degenerates within one or two weeks (periodic, or menstrual, corpus luteum); if, however, the ovum is fertilized and pregnancy begins, the corpus luteum grows very rapidly (corpus luteum of pregnancy) and is retained throughout the greater part of pregnancy, secreting the hormone progesterone, which is necessary for the maintenance and development of the pregnancy.
The term “corpus luteum” is sometimes applied to the aggregate of follicular cells formed in the ovary at the site of discharge of the mature ovum in some invertebrates (insects) and in the majority of vertebrates (amphibians, reptiles, and birds).