LIPID MINITOPICS

Lipids I
Lipids II
Review
 Elmhurst College
Hydrogenation Micelle Anabolic Steroids  Chemistry Department
Olestra Detergents and Surfactants Birth Control  Virtual ChemBook


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Birth Control

Introduction:

Sex hormones are also steroids. The primary male hormone, testosterone, is responsible for the development of secondary sex characteristics. Two female sex hormones, progesterone and estrogen control the ovulation cycle. Notice that the male and female hormones have only slight differences in structures, but yet have very different physiological effects.

Progesterone - Chime in new window

Quiz: List three functional groups in progesterone?  
What is difference between progesterone and testosterone?  
What is difference between testosterone and estrogen?  

Ovarian Cycle:

The ovarian cycle begins when FSH (follicle stimulating hormone) from the pituitary gland stimulates the development of the egg in the ovary. The egg follicle (sack surrounding the egg) secretes estrogen hormones. The estrogens stimulate the lining of the uterus to prepare for receiving a fertilized egg. As the estrogens increase and FSH output decreases, another hormone LH (luteinizing hormone) is secreted by the pituitary to complete the development and eject the egg from the ovary (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. The conditions are summarized in the graph on the left


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Birth Control Pills:

It was discovered relatively long ago (1930's) that injections of progesterone were effective as a contraceptive in preventing pregnancies. The synthesis of similar but slightly different steroids as mimics to the natural steroids led to the development of the "pill".

The "pill" is an oral contraceptive containing synthetic derivatives of the female sex hormones, progesterone and estrogen. These synthetic hormones prevent ovulation and thus prevent pregnancy. The two synthetic hormones in the "pill" deceive the body into thinking it is pregnant. 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.

Ortho Tri-Cyclen acts as earlier birth control pills did, by inhibiting ovulation. Ortho Tri-Cyclen is a 28 pill system where the progestin and norgestimate levels increase in every seven day set of pills. The first seven white tablets contain 0.180 mg of norgestimate and 0.035 mg of ethynyl estradiol. There are seven light blue tablets that contain 0.215 mg of norgestimate and 0.035 mg of ethinyl estradiol, and the seven blue tablets contain 0.250 mg of norgestimate and 0.035 mg of ethinyl estradiol. The final seven pills of the 28-day pack are green placebo pills, or reminder pills (Ortho Tri-Cyclen).

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.

Quiz: Compare the structures of the above two steroids with the natural steroids, progesterone and estrogen. Which one most closely resembles or mimics progesterone?  
Which one most closely resembles or mimics estrogen  

 
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Other Methods of Birth Control:

Implants:

In addition to oral contraceptives, other forms of contraceptives are used. Norplant was released as an implant form of contraception in 1990. Six thin, flexible plastic implants, each containing a hormone called levonorgestrel, much similar to the progesterone made by the ovaries, are inserted under the skin of the upper arm. A clinician must do the insertion of these implants while the patient is under a local antiseptic.

The implants begin releasing levonorgestrel into the bloodstream 24 hours after the capsules have been implanted . The bloodstream carries the hormone to the pituitary gland in the brain, the uterus and the cervix. The pituitary gland then stops the ovaries from developing eggs. The levonorgestrel also keeps sperm from entering the uterus by thickening the cervical mucus and thinning the lining of the uterus. The implants continue to release levonorgestrel for five years.

Long Term Injections:

The FDA approved Depo-Provera, in 1992as a primary injectable contraceptive. Users of the drug receive a shot every 12 weeks, each containing a dose of depo-medroxyprogesterone acetate equaling 150 mg. The drug then causes ovulation to cease by decreasing FSH/LH levels and also a low LH surge. Finally, a cervical mucus, much similar to that caused by Norplant, occurs in order to prevent semen from entering the uterus. Depo-Provera is often recommended for users whose schedule is too busy to take the pill daily and also need to avoid estrogen side effects.

RU-486 - Mifepristone:

Open graphic of RU-486 in a new window

Sometimes known as the abortion pill, RU-486 is widely used in France and China, and was recently approved under tight controls in the U. S. RU-486 works by binding to the progesterone receptor sites. Without progesterone the lining of the uterus breaks down, shedding it and the newly implanted embryo. It also initiates contractions. The drug has side effects and has been very controversial. RU-486 information.