Hormones behind periods or periods behind obstruction

Regular menstrual bleeding depends on a regular rise and fall in hormones from the ovary, the details of which are on WebPage 3.

Briefly, this is achieved by development of follicles, which secrete the ovary's first hormone estrogen (specifically estradiol), followed by ovulation and production, by the corpus luteum, of progesterone, the ovary's second hormone.

Because it takes an average of about two weeks for a follicle to grow to the point of ovulation (the follicular phase), and because the corpus luteum lasts about two weeks (the luteal phase), the ordinary ovarian cycle, and therefore the menstrual cycle, lasts about four weeks (with a normal range that varies between 24 days and 35 days).

Shorter or longer cycles are chiefly brought about by variation of the follicular phase. The luteal phase is more constant.

The lining of the uterus, the endometrium, is built up by estrogen and is then transformed to be receptive to pregnancy by progesterone.

The follicular phase in the ovary, during which only estrogen is released, is the proliferative phase in the endometrium (meaning that the endometrium proliferates, or grows, getting thicker and thicker).

The luteal phase in the ovary, when progesterone is produced, is the secretory phase in the endometrium, as further proliferation is inhibited and the endometrium transforms its energies from growth to differentiation, accumulating secretions to benefit an implanting embryo.

If there's no ovulation -- if there's no progesterone or exposure to a progestogen -- the endometrium can keep proliferating, getting thicker and thicker, and become "hyperplastic" (we call the condition endometrial hyperplasia).

In the absence of ovulation (and in the absence of progesterone or a progestogen), the endometrium can bleed from just the loss of estrogen support.

A swing up and down in estrogen can be enough to cause serious bleeding when the endometrium is thick.

Unlike a normal menstrual period at the end of exposure to progesterone (or progestogen), such an anovulatory period does not cause the whole endometrium to be shed; often the bleeding occurs from patches of it; sooner or later it starts growing again and building up further.

We call this anovulatory dysfunctional uterine bleeding.

There's only a fine hormonal line between amenorrhea and anovulatory dysfunctional uterine bleeding: the hormonal disturbance underlying them can be virtually the same.

There will also be amenorrhea if there is no uterus (see WebPage 18) or if the endometrium in the uterus has been destroyed (endometrial atrophy) or replaced with intrauterine adhesions (see WebPage 17).

Cryptomenorrhea, or "hidden menstruation", is apparent amenorrhea, resulting from an obstruction to menstruation such as an incompletely formed vagina or a transverse vaginal septum (see WebPage 18).

Whereas amenorrhea itself is usually harmless and painless, cryptomenorrhea is cyclically painful and can cause complications, including endometriosis, while it's unrelieved.

Primary amenorrhea is when there have been no periods in a woman's life. The most common causes (beyond a simple delay from not having enough weight yet or exercising a lot) are primary ovarian failure (puberty fails as well) and congenital absence of the uterus and vagina (breast and pubic hair development are normal; discussed on WebPage 18).

Secondary amenorrhea is when the periods have stopped after having been present; its most common causes are hypothalamic anovulation, hyperprolactinemia, polycystic ovary syndrome and early menopause (all discussed in the main text), and intrauterine adhesions (discussed on WebPage 17).