How Do FSH and LH Work?
Let’s take an average twenty-eight-day menstrual cycle, when you aren’t pregnant. We’ll start with day 1. You have just started your period. Your estrogen and progesterone levels are practically nil. The lack of hormones in your system is what has induced you to get your period. GnRH from the hypothalamus and FSH from the pituitary are excreted in response to the level of estrogen circulating in your bloodstream. On day 1, as the blood washes against the hypothalamus and anterior pituitary, there’s practically no estrogen in it. The hypothalamus thus sends out its hormone GnRH to wake up the pituitary. The receptors on the cells that make up the anterior pituitary gland respond to the rise in GnRH and the lack of estrogen in the bloodstream. Their response is to release FSH into the bloodstream. The presence of FSH stimulates the ovaries and adrenals to start making estrogen. For the following ten days of the normal cycle, the anterior pituitary gland will be pouring out FSH to stimula
