Hormones

The menstrual cycle is controlled by a complex system of interrelated hormones that are manufactured by and released within the body. The word hormone (HOR-moan) is derived from the Greek word meaning, "to set in motion," and that's exactly what hormones do. Hormones are released from glands into blood vessels and travel to other organs where they take their effects. There are many glands that make up the endocrine system. Those glands that are involved in menstruation are the hypothalamus, pituitary gland (also known as the "master gland,") and the ovaries.

The hormonal changes that affect the reproductive system begin in the hypothalamus. The hypothalamus is a specialized area of the brain very near the pituitary gland. It is also know as the "pulse generator". The hypothalamus is given this name because it releases Gonadotropin-releasing hormone (GnRH) in a tightly regulated pattern of pulses into the blood vessels that travel to the pituitary gland. The following hormones are intricately involved in the menstrual cycle:

Gonadotropin-releasing hormone (GnRH): is a releasing factor responsible for the production and release of follicle-stimulating hormone (FSH) and luteinizing hormone (LH) from the pituitary gland. As mentioned above, GnRH is released in a pulse-like fashion. The timing of these pulses and the amount of GnRH that is released vary throughout the menstrual cycle. Disturbances in the patterns of GnRH release can disrupt normal ovulatory function. It is believed that menstrual disturbances caused by excessive physical activity, extreme dieting, or stress are related to GnRH production.

The two pituitary gland hormones that influence reproductive function are follicle-stimulating hormone and luteinizing hormone.

Follicle-stimulating hormone: Follicle-stimulating hormone (FSH) is one of the hormones that regulates reproductive function. As we discussed earlier, a woman is born with millions of immature eggs inside her ovaries, and each egg is contained in a group of cells called a follicle. FSH stimulates the specialized cells of the follicle to develop, mature and produce estrogen.

Luteinizing hormone: Luteinizing hormone (LH) is another hormone that is involved in reproductive function and plays three roles in the menstrual cycle. The first, in conjunction with FSH, is to stimulate estrogen production in the follicles. Secondly, the surge of LH at midcycle is responsible for ovulation. Finally, during the luteal phase, LH feeds the corpus luteum.

Estrogen: Estrogen is the female hormone that is secreted from the follicles in the ovaries. Although we use one name to describe this hormone, a woman's body actually produces several varieties of estrogen. The primary product of the ovary is estradiol, which is one form of estrogen. In addition to the ovaries, estrogen is also produced by fat cells throughout the body by converting male hormones into estrogen. However, this form of estrogen production is not governed by menstrual cyclicity. After menopause, when estrogen production in the ovaries has greatly diminished, production of estrogen continues in fat cells.

Although the reproductive system is its primary target, estrogen can enter many cells in the body. The normal effects of estrogen include the following:

•Maturation of the vagina, uterus, fallopian tubes and the breasts during puberty •Controls growth of the bones during puberty which accounts for the growth spurt •Cervical mucus production at ovulation •Growth of the endometrium •Regulation of FSH and LH release •Maintenance of soft, lubricated vaginal tissue •Increase in skin thickness and water content •Protection against bone density loss •Regulation of cholesterol levels, both HDL and LDL •Involvement in lactation •Possible involvement in cognitive abilities and psychological function

Progesterone: After ovulation, the ovary manufactures progesterone. It is found in very high levels during pregnancy. In fact, its name was derived from the terms "pro" (supporting) and "gestation" (pregnancy). The chemical structure of progesterone is somewhat similar to that of estrogen. However, the effects of progesterone are different than those of estrogen. They include the following:

•Development of breasts •Along with estrogen, promotion of endometrial development during the premenstrual phase of the cycle and early pregnancy •Reduction in uterine contractions •Production of thick cervical mucus •Triggers PMS •Regulation of FSH and LH release •Slight elevation of basal body temperature from a half to one degree Fahrenheit •Supports the continuation of a pregnancy

Other hormones that are involved in the process of menstruation are:

Androgen: In addition to producing estrogen and progesterone, the ovaries produce small amounts of androgens, male hormones. The ovaries are not able to produce estrogen without first making androgens. Some androgens are converted to estrogen while some are secreted directly from the ovaries. A subtle increase of androgen production can lead to disruptions in the normal monthly cycle. Excess androgens can also cause problems such as acne and facial hair growth.

Prolactin: The production of breast milk is regulated by many hormones, one of which is prolactin. In fact, the only known function of prolactin in humans is lactation. When a woman is not breastfeeding, the release of prolactin is inhibited by the hypothalamus and levels remain low. High prolactin levels can lead to menstrual problems, including oligomenorrhea and amenorrhea. Some women with an elevated prolactin level may also notice a milky, white discharge from their nipples. There are many reasons why people can have an elevated prolactin level, one of which is excessive growth of the cells in the pituitary that secrete prolactin. Another cause is certain medications, such as phenothiazines (a tranquilizer) and some blood pressure medications.

Prostaglandins: Prostaglandins are a family of hormones that are found throughout the body. Prostaglandins have many functions and are involved in: gastrointestinal tract activity, body temperature, ovulation, blood pressure control, kidney function, uterine contractions and in respiratory function. Prostaglandins that are released from the endometrium cause menstrual cramps and are also linked to the nausea, vomiting, and diarrhea that can accompany cramps.

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