Folicular phase

The menstrual cycle begins when blood is first discharged from the uterus. From day 1 to 5, the uterine line continues to break down and is discharged along with varying amounts of blood. A day before menstruation occurs, the hypothalamus produces, gonadotrophin-releasing hormone (GnRH). GnRH triggers the secretion of FSH from the anterior pituitary gland
FSH triggers the development of one or more follicles in the ovary. This is a ball of cells in the ovary containing an oocyte. As an ovarian follicle grows in size, it secretes an increasing amounts of oestrogens
Oestrogen stimulate the repair and gowth of the uterine lining, and the growth of milk-producing tissues in the mammary glands. During the follicular phase, oestrogens are at low concentrations. they inhibit further production of FSH, so that usually only one follicle matures at a time. This is an example of negative feedback; FSH stimulates the production of oestrogen, and oestrogen inhibit the production of FSH. Oestrogen also stimulates the anterior pituitary gland to secret LH. Most of the LH is stored in the anterior pituitary gland during the follicular phase, but some LH is released into the blood and stimulates the mature ovarian folicule to produce another hormone progesterone.

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