Mr. Chapman Biology 30 Birth Control Pills – How They Work

Ovarian Cycle – Post-Ovulation Following ovulation, LTH (luteotrophic hormone) is secreted by the pituitary gland. LTH causes the formation of a tissue called corpus luteum in the uterus. The corpus luteum releases progesterone in increasing amounts. Progesterone has a feedback effect on the pituitary gland and drastically decreases the amounts of FSH and LH hormones released. Further egg development is prevented until after the fate of the ovulated egg has been decided. If the egg has not been fertilized, the corpus luteum disintegrates and forms the menstrual discharge. Another result is a sharp drop in the estrogen and progesterone levels and the cycle starts anew. If the egg has been fertilized and implanted in the uterus, the estrogen and progesterone levels remain high. The high levels prevent further eggs from developing during the duration of the pregnancy.

Birth Control Pills It was discovered relatively long ago (1930's) that injections of progesterone were effective as a contraceptive in preventing pregnancies. Question: Read the previous slide. How would a high level of progesterone prevent pregnancy? The "pill" is an oral contraceptive containing synthetic derivatives of the female sex hormones, progesterone and estrogen.

Birth Control Pills The two synthetic hormones in the "pill" deceive the body into thinking it is pregnant. These synthetic hormones prevent ovulation and thus prevent pregnancy. A high level of progesterone is maintained which inhibits secretions of FSH and LH. The result is that no new egg follicles are developed and no ovulation occurs. For example, Ortho Tri-Cyclen, the most popular birth control today, contains norgestimate and ethynyl estradiol. The triple bond ethyne group on the steroids allows for the oral administration.

The first 21 pills in the package contain various levels of estrogen and progesterone derivatives – this prevents the secretion of FSH and LH, and hence no follicles ever mature and ovulation does not occur. If ovulation does not occur, pregnancy becomes impossible, since there is no egg to fertilize. The final 7 days are placebo pills – they contain no drugs, and allow for menstruation to occur.

To Be Effective... To be effective, a woman who is taking Ortho Tri-Cyclen must take the pills every day at the same time. If taken correctly, this form of oral contraception is up to 99 percent effective. However, if two or more consecutive pills are missed another form of birth control must be used.