How the Pill Works
Raging hormones! Surging hormones!
If you've gone through puberty you can attest to feeling hormones race through your body. Hormones act as messengers within the human body — performing essential functions, not just tormenting teenagers.
The word hormone is derived from the Greek hormaô, "stir up" or "incite." Hormones are chemicals that send information between cells and organs to control metabolic processes. The sex hormones that cause such a ruckus in puberty are crucial to the reproduction process in men and women.
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. Scientific advances in creating synthetic hormones were essential to the development of the birth control pill.
Scroll through a month and monitor the changing balance of hormones in a woman's reproductive cycle. Then "take the pill" to see how synthetic hormones adjust this balance and prevent ovulation.
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
Days 1 - 5
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.
At the hypothalamus and pituitary gland, the estrogen acts to suppress FSH production (providing negative feedback).
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.
Menstrual Cycle with Pill
Alterations to the cycle by the birth control pill:
Days 1 - 5
The pill uses the body's negative feedback system to prevent ovulation and implantation of an embryo, in the same way the hormones provided by the placenta halt the female cycle during pregnancy. Women using birth control pills must remember to take one each day.
Synthetic estrogen and progestin (a form of progesterone) in the pills travel through the bloodstream to the hypothalamus and the pituitary gland. The estrogen suppresses production of FSH in the pituitary gland so follicle maturation doesn't occur.
Days 6 - 10
The pituitary gland steps down production of FSH. Without FSH from the pituitary gland, no dominant follicle develops and there is no increase in estrogen. The uterine lining doesn't thicken.
Days 11 - 13
Constant low levels of progestin send a signal to the hypothalemus and pituitary gland to prevent the LH surge.
Without the LH surge, ovulation doesn't occur and no ovum is released. The constant level of progestin makes the lining of the uterus inhospitable to implantation of an embryo. The cervical mucus remains thick.
Days 15 -21
The continued delivery of estrogen and progestin maintains the suppression of FSH and LH.
Days 22 - 28
Placebo pills without estrogen and progestin allow for the breakdown and release of the thin uterine lining as a withdrawal bleed, similar to menstruation.