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  • This might seem hard to believe, but right now, 300 million women across the planet are experiencing the same thing: a period.

  • The monthly menstrual cycle that leads to the period is a reality most women on Earth will go through in their lives.

  • But why is this cycle so universal? And what makes it a cycle in the first place?

  • Periods last anywhere between two and seven days, arising once within in a 28-day rotation.

  • That whole system occurs on repeat, happening approximately 450 times during a woman's life.

  • Behind the scenes are a series of hormonal controls that fine-tune the body's internal workings to make menstruation start or stop during those 28 days.

  • This inner machinery includes two ovaries stocked with thousands of tiny sacks called follicles that each contain one oocyte, an unfertilized egg cell.

  • At puberty, ovaries hold over 400 thousand egg cells but release only one each month, which results in pregnancy or a period.

  • Here's how this cycle unfolds.

  • Each month beginning around puberty, the hormone-producing pituitary gland in the brain starts releasing two substances into the blood: follicle-stimulating hormone and luteinizing hormone.

  • When they reach the ovaries, they encourage the internal egg cells to grow and mature.

  • The follicles respond by pumping out estrogen.

  • The egg cells grow and estrogen levels peak, inhibiting the production of FSH, and telling the pituitary to pump out more LH.

  • That causes only the most mature egg cell from one of the ovaries to burst out of the follicle and through the ovary wall.

  • This is called ovulation, and it usually happens ten to sixteen days before the start of a period.

  • The tiny oocyte moves along the fallopian tube.

  • A pregnancy can only occur if the egg is fertilized by a sperm cell within the next 24 hours; otherwise, the egg's escapade ends, and the window for pregnancy closes for that month.

  • Meanwhile, the now empty follicle begins to release progesterone, another hormone that tells the womb's lining to plump up with blood and nutrients in preparation for a fertilized egg that may embed there and grow.

  • If it doesn't embed, a few days later, the body's progesterone and estrogen levels plummet, meaning the womb stops padding out and starts to degenerate, eventually falling away.

  • Blood and tissue leave the body, forming the period.

  • The womb can take up to a week to clear out its unused contents, after which, the cycle begins anew.

  • Soon afterwards, the ovaries begin to secrete estrogen again, and the womb lining thickens, getting ready to accommodate a fertilized egg or be shed.

  • Hormones continually control these activities by circulating in ideal amounts delivered at just the right time.

  • The cycle keeps on turning, transforming each day and each week into a milestone along its course towards pregnancy or a period.

  • Although this cycle appears to move by clockwork, there's room for variation; women and their bodies are unique, after all.

  • Menstrual cycles occur at different times in the month, ovulation comes at various points in the cycle, and some periods last longer than others.

  • Menstruation even begins and ends at different times in life for different women, too; in other words, variations between periods are normal.

  • Appreciating these differences and learning about this monthly process can empower women, giving them the tools to understand and take charge of their own bodies.

  • That way, they're able to factor this small cycle into a much larger cycle of life.

This might seem hard to believe, but right now, 300 million women across the planet are experiencing the same thing: a period.

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B2 US TED-Ed cycle egg estrogen pregnancy hormone

【TED-Ed】How menstruation works - Emma Bryce

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    SylviaQQ posted on 2021/07/26
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