Hormonal Changes during the Menstrual Cycle

During the menstrual cycle, a series of hormonal changes occur in the female body, orchestrated by the hypothalamus, pituitary gland, ovaries, and uterus. These hormonal fluctuations regulate the different phases of the menstrual cycle, including menstruation, follicular phase, ovulation, and luteal phase.

Menstruation
- The menstrual cycle begins with the shedding of the uterine lining, known as menstruation.
- During this phase, the levels of estrogen and progesterone are low.
- The low hormone levels trigger the hypothalamus to release gonadotropin-releasing hormone (GnRH).

Follicular Phase
- In response to GnRH, the pituitary gland releases follicle-stimulating hormone (FSH).
- FSH stimulates the development of ovarian follicles, each containing an egg.
- The growing follicles produce estrogen, which thickens the uterine lining.
- As the follicular phase progresses, one dominant follicle emerges, and the others regress.

Ovulation
- The surge in estrogen triggers a sudden release of luteinizing hormone (LH) from the pituitary gland.
- The surge in LH stimulates the release of the mature egg from the dominant follicle, a process known as ovulation.
- Ovulation usually occurs around the 14th day of a 28-day menstrual cycle.

Luteal Phase
- After ovulation, the ruptured follicle transforms into the corpus luteum.
- The corpus luteum secretes high levels of progesterone, which prepares the uterus for potential implantation of a fertilized egg.
- Progesterone also inhibits further ovulation.
- If fertilization does not occur, the corpus luteum degenerates, leading to a decline in progesterone and estrogen levels.
- The drop in hormone levels triggers the shedding of the uterine lining, marking the start of a new menstrual cycle.

Key Hormones Involved
- Gonadotropin-releasing hormone (GnRH): Released by the hypothalamus, stimulates the release of FSH and LH.
- Follicle-stimulating hormone (FSH): Released by the pituitary gland, promotes the development of ovarian follicles.
- Luteinizing hormone (LH): Released by the pituitary gland, triggers ovulation and the formation of the corpus luteum.
- Estrogen: Produced by growing ovarian follicles, thickens the uterine lining.
- Progesterone: Secreted by the corpus luteum, prepares the uterus for implantation and inhibits further ovulation.

Understanding the hormonal changes during the menstrual cycle is crucial for reproductive health and fertility. Any imbalances in these hormones can potentially lead to irregular menstrual cycles or fertility issues.