Female Reproductive System
Getting To Know Your Body
Follicle Stimulating Hormone
Follicular Development Based on Hormones
The production and release of follicle stimulating hormone is regulated by the levels of a number of circulating hormones released by the ovaries and testes. This system is called the hypothalamic-pituitary-gonadal axis.
In women, when hormone levels fall towards the end of the menstrual cycle, this is sensed by nerve cells in the hypothalamus. These cells produce more gonadotrophin-releasing hormone which in turn stimulates the pituitary gland to produce more follicle stimulating hormone and luteinising hormone and release these into the bloodstream. The rise in follicle stimulating hormone stimulates the growth of the follicle in the ovary. With this growth, the cells of the follicles produce increasing amount of oestradiol and inhibin. In turn, the production of these hormones is sensed by the hypothalamus (or pituitary gland in the case of inhibin) and less gonadotrophin-releasing hormone and follicle stimulating hormone will be released. However, as the follicle matures, there is a surge in oestradiol production which switches the feedback mechanisms in the brain from negative to positive feedback, causing more gonadotrophin-releasing hormone, follicle stimulating hormone and luteinising hormone to be released. This peak in hormone levels eventually leads to ovulation.
Pregnancy & Hormones
Estrogen and progesterone are the chief pregnancy hormones. A woman will produce more estrogen during one pregnancy than throughout her entire life when not pregnant. The increase in estrogen during pregnancy enables the uterus and placenta to improve vascularization, transfer nutrients, and support the developing baby. In addition, estrogen is thought to play an important role in helping the fetus develop and mature. Estrogen levels increase steadily during pregnancy and reach their peak in the third trimester. The rapid increase in estrogen levels during the first trimester may cause some of the nausea associated with pregnancy and, during the second trimester, plays a major role in the milk duct development that enlarges the breast.