JEAN-CLAUDE REVY-A. GOUJEON, ISM / SCIENCE PHOTO LIBRARY JEAN-CLAUDE REVY-A. GOUJEON, ISM / SCIENCE PHOTO LIBRARY
Human ovary. Light micrograph of a section through a human ovary at the start of the luteal phase (roughly between the 15th and 19th day) of the menstrual cycle. The pink structure at top is the corpus luteum, which is formed after ovulation (around day 14 of the 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. The white ovals are follicles. Once sexual maturity is reached, up to 20 primordial follicles are triggered to start developing into primary follicles every menstrual cycle. Only one will reach full maturity and release its egg (ovum) at ovulation.
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