Menstrual cycle, drawing
Illustration of hormonal levels during the menstrual cycle without fertilisation of the egg. The menstrual cycle repeats every 28 days or so. On the first day of periods, the brain starts to secrete FSH, whch stimulates the ovaries. For 14 days, this hormone favours the secretion of estrogen and the maturing of the future egg. A few days after ovulation, the brain starts to secrete LH. On the 14th day of the cycle, levels of LH in the blood are high : ovulation takes place and the ovary starts to secrete progesterone. This hormone thickens the uterine lining (the endometrium) and gets it ready to receive the egg. Under the effect of the progesterone, the brain progessively stops secreting FSH and LH : the ovaries diminish their production of estrogen, then progesterone, until the following cycle. The reduction of levels of all these hormones in the blood is responsible for triggering periods. The close up at top right shows what happens at the end of the luteal phase.
Size: 4034px × 4960px
Location: Bas-Rhin
Photo credit: © JACOPIN / BSIP / Alamy / Afripics
License: Licensed
Model Released: No
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