<P> Like the previous theca cells, the theca lutein cells lack the aromatase enzyme that is necessary to produce estrogen, so they can only perform steroidogenesis until formation of androgens . The granulosa lutein cells do have aromatase, and use it to produce estrogens, using the androgens previously synthesized by the theca lutein cells, as the granulosa lutein cells in themselves do not have the 17α - hydroxylase or 17, 20 lyase to produce androgens . Once the corpus luteum regresses the remnant is known as corpus albicans . </P> <P> The corpus luteum is essential for establishing and maintaining pregnancy in females . The corpus luteum secretes progesterone, which is a steroid hormone responsible for the decidualization of the endometrium (its development) and maintenance, respectively . It also produces relaxin, a hormone responsible for softening of the pubic symphysis which helps in parturition . </P> <P> If the egg is not fertilized, the corpus luteum stops secreting progesterone and decays (after approximately 10 days in humans). It then degenerates into a corpus albicans, which is a mass of fibrous scar tissue . </P> <P> The uterine lining (endometrium) is expelled through the vagina (in mammals that go through a menstrual cycle). In an estrous cycle, the lining degenerates back to normal size . </P>

What happens to corpus luteum if egg is fertilized
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