A Woman and Her Hormones

At puberty, hormones will begin to make a lasting change to a girl's body. Her breasts will get bigger and take on the shape of an adult woman's breasts. She will develop underarm and pubic hair and will get obviously taller as a growth spurt occurs. Sooner or later her periods will start, usually as the growth spurt is beginning to slow down. From beginning to end, the process of puberty usually takes at least three to four years. All the mechanism necessary for going through puberty is present at birth, but the body has it turned off some years. Eventually, the mechanism that prevents puberty winds down, and hormones that previously have been held in check can begin to put forth their influence on the body. A part of the brain called the hypothalamus starts to release more and more large and frequent pulses of a hormone called gonadotrophin-releasing hormone. This stimulates the brain to start producing other hormones in a girl's ovaries.

The most important hormones made by the ovaries are known as female sex hormones and the two main ones are estrogen and progesterone. The ovaries also produce some of the male hormone, testosterone. During puberty, estrogen stimulates breast development and causes the vagina, uterus and fallopian tubes to mature. Testosterone helps to promote muscle and bone growth.

From puberty onwards, FSH, estrogen and progesterone all play a vital part in regulating a woman's menstrual cycle, which results in her periods. Each individual hormone follows its own pattern, rising and falling at different points in the cycle, but together they produce a predictable chain of events.

One egg becomes ripe and is released from the ovary to begin its journey down the fallopian tube and into the womb. If that egg isn't fertilized, the levels of estrogen and progesterone produced by the ovary begin to fall. Without the supporting action of these hormones, the lining of the womb, which is full of blood, is shed, resulting in a period.

As the primary female hormone, estrogen promotes the growth and health of the female reproductive organs and keeps the vagina moisturized, stretchy, and well supplied with blood. Estrogen levels generally decline during perimenopause, but they do so in an irregular fashion. Sometimes there can be more estrogen present during perimenopause than in the past.

Intermittent decreases in progesterone affect menstrual periods more than they affect sexual function, but age related declines in testosterone may reduce sex drive in midlife women, although this remains controversial. The fact that estrogen declines more than testosterone leads some to believe that libido should not decline at menopause. The decline in testosterone in women is solely age related, not menopause related, and begins years before perimenopause.

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