Introduction:

The Reproductive System

The primary structures in the reproductive system are:

• The uterus is a pear-shaped organ located between the bladder and lower intestine. It consists of two parts, the body and the cervix.
• When a woman is not pregnant the body of the uterus is about the size of a fist, with its walls collapsed and flattened against each other. During pregnancy the walls of the uterus are pushed apart as the fetus grows.
• The cervix is the lower portion of the uterus. It has a canal opening into the vagina, with an opening called the os, which allows menstrual blood to flow out of the uterus into the vagina.
• Leading off each side of the body of the uterus are two tubes, known as the fallopian tubes. Near the end of each tube is an ovary.
• Ovaries are egg-producing organs that hold 200,000 - 400,000 follicles (from folliculus, meaning "sack" in Latin). These cellular sacks contain the materials needed to produce ripened eggs, or ova.
• The inner lining of the uterus is called the endometrium. During pregnancy it thickens and becomes enriched with blood vessels, which house and support the growing fetus. If pregnancy does not occur, the endometrium is shed as part of the menstrual flow. Menstrual flow also consists of blood and mucus from the cervix and vagina.

The uterus is a hollow muscular organ located in the female pelvis between the bladder and rectum. The ovaries produce the eggs that travel through the fallopian tubes. Once the egg has left the ovary it can be fertilized and implant itself in the lining of the uterus. The main function of the uterus is to nourish the developing fetus prior to birth.

Stages and Features of Menstruation

Onset of Menstruation (Menarche). The onset of menstruation, called the menarche, typically begins between the ages of 12 - 13 years. Menarche generally occurs 2 - 3 years after initial breast development (breast budding). African-American and Hispanic girls tend to mature slightly earlier than Caucasian girls. A higher body mass index (BMI) during childhood is associated with an earlier onset of puberty. Environmental factors and nutrition may also affect menarche timing.

Length of Monthly Cycle. The menstrual cycle can be very irregular during the first 1 - 2 years, ranging from 21 - 45 days. The length then generally stabilizes to an average of 28 days, although the cycle length may range from 21 - 34 days and still be considered normal. A variation of 10 days or more -- either more or fewer days -- may have an impact on fertility, however. When a woman reaches her 40s the cycle lengthens, reaching an average of 31 days by age 49. A number of factors can affect cycle length at any age.

Length of Periods. Periods average 6.6 days in adolescent girls. By the age of 21, menstrual bleeding averages 6 days until women approach menopause. However, about 5% of healthy women menstruate fewer than 4 days, and 5% menstruate more than 8 days.

Normal Absence of Menstruation. Normal absence of periods can occur in any woman under the following circumstances:

• Menstruation stops during pregnancy. Some women continue to have irregular bleeding during the first trimester. This bleeding may indicate a threatened miscarriage and requires immediate attention by the doctor.
• When women breastfeed they are unlikely to ovulate. After that time, menstruation usually resumes and they are fertile again.

Perimenopause starts when the intervals between periods begin to lengthen, and it ends with menopause itself (the complete cessation of menstruation). Menopause usually occurs at about age 51, although smokers often go through menopause earlier.