Mr. Chapman Biology 30 Birth Control Pills How They Work
Slide 2
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.
Slide 3
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.
Slide 4
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.
Slide 5
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.
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Slide 8
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.