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The Pill
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How the Pill Works
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How the Pill Works

The physical, and sometimes emotional, changes a woman goes through on a monthly basis are caused by hormones that work together, communicating between the brain and the reproductive system. The birth control pill jumps into this relay system midstream, delivering two key sex hormones that trick the brain into thinking the body is already pregnant.

View the phases of activity in each monthly cycle and monitor the changing hormonal levels.

Female Menstrual Cycle | Menstrual Cycle with Pill

Days 1 - 5
Menstruation begins.

Low levels of progesterone and estrogen cause the hypothalamus to send a releasing hormone (GnRH) to the pituitary gland.

The releasing hormone signals the pituitary gland to release FSH (follicle stimulating hormone) and LH (luteinizing hormone).

FSH and LH travel from the pituitary gland to the ovaries via the bloodstream. The FSH causes the maturation of the follicles in the ovaries -- each follicle consists of an egg (ovum) surrounded by cells that produce estrogen.

Days 6 - 10
One dominant follicle develops that will release a single ovum in the cycle. The production of estrogen increases throughout the first half of the cycle.

The estrogen travels through the bloodstream to the reproductive organs and also to the hypothalamus and pituitary gland. The endometrium, which is the lining of the uterus, begins to thicken as a result of the estrogen.

Days 11-13
At the hypothalamus and pituitary gland, the estrogen acts to suppress FSH production (providing negative feedback).

Day 14
Consistently high levels of estrogen cause the pituitary gland to release a massive LH surge, which triggers ovulation. The dominant follicle bursts, releasing a mature ovum that travels to the fallopian tubes. Mucus on the cervix thins to become more permeable to sperm.

Days 15 - 22
After releasing the ovum, the ruptured follicle is transformed into the corpus luteum, a mass of cells that produces progesterone. Progesterone is the predominant sex hormone in the second half of the cycle and makes the thickened endometrium favorable for implantation of the embryo (the fertilized ovum).

The progesterone signals the hypothalamus and pituitary gland to suppress FSH and LH production, ensuring that no more follicles mature.

Days 23 - 25
If there is no fertilization of the ovum by sperm, the corpus luteum deteriorates and production of progesterone stops. If fertilization has occurred, the corpus luteum continues to produce progesterone, a function which is ultimately taken over by the placenta, an organ which nourishes the growing fetus of a successful pregnancy.

Days 27 - 28
The uterine lining begins to break down with a decrease of progesterone and will be released at menstruation.

The cycle begins again.



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