The menstrual cycle, an orchestrated interplay of several hormones, is a key facet of female reproductive health. From the initiation of menstruation during puberty to its cessation at menopause, the hormonal ebb and flow govern fertility and cyclical physiological changes. The hormones involved - principally, Follicle Stimulating Hormone (FSH), Luteinizing Hormone (LH), Estrogen, and Progesterone - regulate the intricate processes of follicular maturation, ovulation, and the uterine lining's preparation for a potential pregnancy. 

Hormonal Regulation of the Menstrual Cycle

The menstrual cycle, typically 28 days long, is divided into three phases: the follicular phase, ovulation, and the luteal phase.

1) Follicular Phase:

The follicular phase begins on the first day of menstruation and lasts until ovulation. During this phase, the hypothalamus releases Gonadotropin-Releasing Hormone (GnRH), stimulating the pituitary gland to secrete FSH and LH. FSH encourages the growth and maturation of several follicles in the ovaries. Each follicle houses an immature egg (oocyte), and usually, only one will reach full maturity.

These developing follicles produce Estrogen, causing a substantial rise in its levels. Estrogen serves two primary functions. Firstly, it stimulates the growth and thickening of the endometrium (the inner lining of the uterus), preparing it for the potential implantation of an embryo. Secondly, as Estrogen levels peak towards the end of the follicular phase, it triggers a surge of LH from the pituitary gland, setting the stage for ovulation.

2) Ovulation:

Ovulation, the release of a mature egg from the dominant follicle in the ovary, typically occurs around the 14th day of the cycle. The process is primarily induced by the surge in LH secretion, a response to the peak in Estrogen levels. The egg is then swept into the fallopian tube, where it is available for fertilization by sperm.

3) Luteal Phase:

The luteal phase follows ovulation and is characterized by the formation of the corpus luteum, the remnants of the follicle that released the egg. The corpus luteum secretes Progesterone, and to a lesser extent, Estrogen. Progesterone further prepares the endometrium for possible embryo implantation by promoting vascularization and glandular secretion. If fertilization and implantation occur, Progesterone supports early pregnancy until the placenta is sufficiently developed to take over hormone production.

If pregnancy does not occur, the corpus luteum disintegrates, leading to a sharp decrease in Progesterone and Estrogen levels. This hormonal withdrawal triggers the shedding of the endometrial lining, culminating in menstruation and marking the start of a new cycle.

Hormonal Interactions and Feedback Loops

The orchestration of the menstrual cycle involves complex interactions and feedback mechanisms between the hypothalamus, pituitary gland, and ovaries - the so-called hypothalamic-pituitary-gonadal (HPG) axis. When Estrogen levels are low at the beginning of the cycle, the hypothalamus releases GnRH, stimulating the pituitary to produce FSH and LH. As the follicles develop and Estrogen levels rise, a negative feedback mechanism reduces the secretion of GnRH, FSH, and LH to prevent overproduction. However, when Estrogen levels reach a critical peak, they exert a positive feedback effect, inducing the surge of LH that triggers ovulation.