Birth Control

Birth control acts to prevent the spermatozoa and ovum from coming together, to prevent ovulation, or to prevent implantation. Here are the ways that are generally used...

Behavioral Birth Control

In this category go any behaviors that one can display to prevent pregnancy. Therefore, all of these birth control methods involve some modification of sexual behavior. Your book doesn't even mention abstinence, which is certainly a behavioral mode that prevents pregnancy. I think the book only considers birth control in sexually-active individuals. Keep in mind that modification of sexual activity is not always a method of choice anyway for individuals. If I think of how many diets I have messed up because of temptation, I can understand how mere behavioral modification is not going to work well for most. In addition, the methods of behavioral birth control are lacking in effectiveness; they are certainly NOT recommended methods. The methods mentioned in your book are coitus interruptus and the rhythm method.

Coitus interruptus is when a male removes his penis from the female's vagina prior to ejaculation. This is not reliable because some semen may escape before ejaculation and because the timing required to prevent internal ejaculation is not easy. The rhythm method assumes that a woman can determine when she is most fertile and not have intercourse during that time. This is not very reliable because the estimation of when an individual is "most fertile" can be off.

An interesting aside... In the absence of artificial light, a woman's body can adjust its cycle to the cycle of the moon-- which is 28 days. In this condition, the women in a community will all have coordinated cycles, so that they are typically all menstruating at the same time. I have heard stories about how, in ancient times, women used to have gatherings at the time of their greatest fertility... only those women who wanted to become pregnant would not attend the meetings. Sort of an historic, communal behavioral birth control. I do not have any sources for this story, but I have heard it from enough reliable resources that I believe it to be true.

Barriers for Birth Control

Mechanical Barrier

The condom, diaphragm, and cervical cap are all forms of mechanical barriers against fertilization. All three of these devices serve to prevent the semen from entering the uterus. However, because some spermatozoa may be able to sneak through a mechanical barrier, it is recommended that a chemical barrier be used in conjunction with the mechanical barriers.

Chemical Barrier

Chemicals that prevent the spermatozoa from functioning are useful in birth control. Spermicides (to kill spermatozoa) and the solutions that typically house the spermicides are quite effective in hindering the travel of spermatozoa. Of course, not all spermatozoa are killed, and hindering the spermatozoa is not the same as completely effective destruction of them, so it is recommended that chemical barriers be used in conjunction with other methods, like mechanical barriers.

Hormonal Birth Control

Your book describes three modes of hormonal delivery: oral contraceptive ("the pill"), implanted contraceptive (under the skin), and injected contraceptive ("Depo-Provera"). In all three cases, the main ingredient in the birth control chemical is progesterone. By giving progesterone doses, the woman's body does not typically experience any prolonged period where estrogen is in higher concentration than progesterone in the body. Therefore, ovulation does not occur.

If ovulation is prevented, fertilization is prevented. This method of birth control stops when the hormone is no longer administered.

Note that typical oral contraceptive have a woman take 21 pills of progesterone + other ingredients, and then 7 pills that lack the hormone. Remember that when progesterone levels fall normally, that causes the endometrial lining to be slouged off and menstruation occurs. When a woman taking oral contraceptives switches from the ones with progesterone to the ones without, she experiences a similar drop in progesterone levels and that is when menstruation occurs.

Surgical Birth Control

In males, this is called a vasectomy, and in females, a tubal ligation. In both cases, the tube that carries the gamete from the gonad (vas deferens in males and uterine tube in females) is cut and tied off. This prevents the gametes from ever being involved in fertilization.

Typically, these surgeries are reversible... although not always. Therefore, they are usually only recommended if an individual is sure that they do not want any more children.

Other

Your book puts the IUD (intrauterine device) in this category. This device interferes with zygote implantation (not necessarily fertilization), preventing pregnancy.

Sexually-Transmitted Diseases

Your book only has a tiny section on this... what I am giving you is even less.

During sexual intercourse, there is an exchange of body fluids between two individuals. The exchange certainly includes the transfer of semen from the male to the female. But there is more than simply that. Bleeding can occur in either (or both) individuals. The female secretes a mucous-like fluid. Any pus-containing skin areas can erupt as well. Note: whether the sex is heterosexual or homosexual, exchange of body fluids occurs.

Body fluids can contain infectious agents as well as the specific items that we have studied this semester. If you take microbiology, you will learn more about these infectious agents. But the overall notion for us in A&P is that intercourse does allow certain infections to spread from one individual to another. Not all of the symptoms of a sexually-transmitted disease display themselves in the reproductive systems-- certainly, some diseases passed in this manner are systemic (like AIDS).

Note that a mechanical barrier for birth control that more completely prevents any mixing of body fluids (like male and female condoms) are somewhat effective (but not completely effective) in preventing the spread of STDs.