Corpus luteum. Light micrograph of a section through a human ovary showing the corpus luteum (pink) during pregnancy. The corpus luteum is formed after ovulation (around day 14 of the ovarian cycle) from the ovarian follicle that released the egg. The function of the corpus luteum is to secrete the hormone progesterone to ready the uterus for the implantation of a fertilised egg. If the egg is not fertilised it stops secreting and degrades after roughly 12 days. If the egg is fertilised and implants in the lining of the uterus (endometrium) the corpus luteum continues to secrete progesterone to maintain the endometrium.
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