ENGL 202C: Technical Definition or Description Assignment

8/8/2019 ENGL 202C: Technical Definition or Description Assignment

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The PillPreventing Pregnancy with Hormones

Megan Scanlan

10/18/2010



SOME BACKGROUND

The Female Reproductive Cycle

The menstrual cycle is a 28 day cycle, beginning on the first day of a womans menstrual period.

Ovulation, the process in which a mature egg (ovum) is released from the ovary, occurs on day 14 of the

menstrual cycle. This opens a 24 hour window for sperm to penetrate the egg (fertilization). However,

because sperm can survive for a few days in the female reproductive tract, this 24-hour window is not

the only time of the month that intercourse may lead to pregnancy.

Once ovulation occurs the ovum enters the uterine (fallopian) tube, where it can become fertilized. If

fertilization occurs, the genetic material of the sperm and egg combine and the fertilized ovum becomes

a zygote. The single-cell zygote divides to become a mass of cells, a morula, which undergoes further

transformation to become a blastocyst. The blastocyst implants in the inner membrane of the uterus,

called the endometrium, about seven days after fertilization has occurred.

Hormone Control

The female reproductive cycle is initiated and

maintained by hormones. The hypothalamus is a

portion of the brain that links the nervous and

endocrine systems of the body via the pituitary

gland, a major organ of the endocrine system

which secretes hormones to regulate

physiological processes. The hypothalamus

releases GnRH (Gonadotrophin-releasing

hormone) to stimulate the anterior pituitary.

LH and FSHWhen stimulated, the anterior pituitary secretes

the gonadotrophins LH (Luteinizing hormone)

and FSH (Follicle-stimulating hormone). LH

stimulates theca interna cells to convert

cholesterol into androstenedione, which

granulosa cells can then use as a precursor to

produce estrogen. The LH surge, an acute rise in

LH levels triggered by a peak in estrogen levels,

causes ovulation to occur.

FSH has several important functions in the

menstrual cycle. Firstly, it initiates the growth of

ovarian follicles. These follicles are aggregations

of cells within the ovary, each containing a single

immature ovum. FSH also stimulates granulosa cells to divide and to produce inhibin and estrogen.

Inhibin provides negative feedback to the anterior pituitary for the production of FSH, which means that

as the levels of inhibin rise in the body, the anterior pituitary is signaled to stop secreting FSH.

Figure 1: Hormone levels of the menstrual cycle.



EstrogenBoth LH and FSH lead to the production of estrogen. This hormone is responsible for the proliferation of

endometrium cells. Estrogen also determines secondary sex characteristics (enlargement of breasts,

growth of body hair, etc.).

At moderate, constant levels, estrogen provides negative

feedback to the anterior pituitary for LH production and to

the hypothalamus for GnRH production. In large doses

however, estrogen provides positive feedback, stimulating

the release of LH. This spike in estrogen concentrations

occurs about mid-cycle, causing the LH surge and thereafter

ovulation. After ovulation occurs, the hormone

progesterone is produced, causing the endometrium to

produce secretions.

THE PRINCIPLE BEHIND THE PILL: HOW IT WORKS

Synthetic Hormones

Birth control pills work through the action of synthetic hormones, specifically estrogen and/or progestin,

a synthetic hormone that acts much like progesterone. These pills prevent pregnancy through many

mechanisms, primarily by stopping ovulation.

Preventing Ovulation

Birth control pills stop ovulation from occurring by preventing the secretion of the Gonadotrophins LH

and FSH. The synthetic hormones of birth control pills stabilize the natural hormone levels of the body.Without the natural mid-cycle spike in estrogen levels, the anterior pituitary is not stimulated to release

LH and FSH. Instead, the moderate, constant estrogen levels provide negative feedback to the anterior

pituitary and hypothalamus, halting LH and FSH production. The LH surge is not triggered, and ovulation

does not occur.

Pills typically come in packs of 21 to 28 pills and are to

be taken regularly at the same time each day in order

to maintain hormone levels in the body. Packs of 28

contain one week of reminder pills (in the picture

shown to the left, the last row of white pills) that do

not contain any hormones. The purpose of these pills

is to keep once-a-day pill-taking habits consistent and

avoid confusion and the chance of missing hormone

pills (in the picture shown to the left, the first three

rows of colored pills).

Packs of 21 do not contain these reminder pil ls. Consumers simply stop taking the hormone pills for

one week, and must be careful to remember when to restart their pill regimen. For both the 21- and 28-

day pill regimens, the menstrual period occurs during this week without hormone-containing pills.

Figure 2: Feedback processes of the

menstrual cycle



Other Mechanisms

The Pill can prevent pregnancy in other ways. Progestin causes changes in the cervical mucous and the

endometrium to enhance the Pills effectiveness. The cervical mucous thickens, preventing sperm from

entering the uterus, and the lining of the uterus thins, preventing implantation.

CONCLUSION In summary, birth control pills use estrogen and/or progestin to regulate the natural hormone levels of

the menstrual cycle. By stabilizing estrogen levels, the LH surge does not occur to trigger ovulation, and

the ovaries do not release an egg to be fertilized. The hormones of the Pill also cause other changes in

the body to decrease the likelihood of becoming pregnant, including changes in the cervical mucous and

changes in the lining of the uterus.

Used properly, birth control pills are 99.8 percent effective. In practice, however, they are only about 90

percent effective. Women can decrease their chances of becoming pregnant by taking birth control pills

regularly, once a day, at the same time every day. A regular schedule is important for stabilizing the

bodys hormone levels, and can drastically increase the effectiveness of the Pill.



WORKS CITED

http://www.drugs.com/cdi/tri-sprintec.html

http://www.merck.com/mmhe/sec22/ch241/ch241e.html

http://www.medicinenet.com/hormonal_methods_of_birth_control/article.htm

Figure 1: http://www.soc.ucsb.edu/sexinfo/article/the-menstrual-cycle

Figure 2:

http://www.cartage.org.lb/en/themes/sciences/lifescience/generalbiology/physiology/ReproductiveSys

tem/HumanReproduction/HumanReproduction.htm

ENGL 202C: Technical Definition or Description Assignment

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