In premature ovarian failure, which is also called primary ovarian insufficiency, the ovaries stop functioning normally, and this means that they stop ovulating, or releasing egg cells, and they also stop producing hormones, mainly estrogen and progesterone, and this all happens before a woman is 40 years old. It’s considered a “primary” problem because the problem is with the ovaries themselves, rather than glands or hormones that act on the ovaries.
Normally, the hypothalamus, which is located at the base of the brain, secretes gonadotropin-releasing hormone, or GnRH. GnRH makes the nearby pituitary gland secrete two hormones of its own, called gonadotropins. These are follicle stimulating hormone, or FSH, and luteinizing hormone, or LH. These hormones travel to the follicles within the ovaries. The follicles are small clusters of granulosa and theca cells that protect the developing egg cell.
FSH acts on the granulosa cells, making the follicles grow and mature, as well as secrete estrogen, while LH stimulates theca cells to secrete progesterone and small amounts of androstenedione, which is a precursor of testosterone. All three of these hormones belong to a class of steroids, or lipid-soluble hormones.
At birth, a woman has millions of follicles, each ready and excited to do its job. During puberty, the monthly menstrual and ovarian cycles begin, which is when the endometrium, or inner lining of the uterus, goes through cyclic changes in response to the ovarian hormones.
During the ovarian cycle, the ovarian hormones also help a handful of follicles to start growing. Eventually, there’s ovulation which is when a single follicle fully matures and ruptures, releasing its egg cell, while the other follicles degenerate and die off.