Menstrual Cycle

Overview of the Menstrual Cycle

  • The menstrual cycle is a biological process that occurs approximately every 28 to 34 days in women and those of other reproductive ages.
  • This cycle prepares the female body for pregnancy, ensuring the production and release of an egg for fertilisation.
  • The menstrual cycle encompasses various segments including the follicular phase, ovulation, the luteal phase, and menstruation.

Follicular Phase

  • The follicular phase begins on the first day of menstruation and lasts until ovulation.
  • The hypothalamus releases GnRH (gonadotropin-releasing hormone) which stimulates the pituitary gland to release FSH (Follicle Stimulating Hormone) and LH (Luteinising Hormone).
  • FSH stimulates the growth of multiple ovarian follicles, each containing a single immature egg or oocyte.
  • The growing follicles release oestrogen which thickens the lining of the uterus (endometrium) to prepare for potential pregnancy.

Ovulation

  • Ovulation typically happens in the middle of the menstrual cycle, around day 14.
  • High levels of oestrogen stimulate a surge in LH, which stimulates the maturation and release of the most dominant follicle’s oocyte from the ovary into the fallopian tube.
  • This egg is then available for fertilisation by sperm.

Luteal Phase

  • After ovulation, the remaining follicle transforms into the corpus luteum, marking the start of the luteal phase.
  • The corpus luteum secretes progesterone, which maintains the thickened lining of the uterus, ready for the possible implantation of a fertilised egg.

Menstruation

  • If fertilisation does not occur, the corpus luteum decomposes, leading to a drop in progesterone levels.
  • This causes the uterus lining to break down and shed, resulting in menstruation.
  • Menstruation is the bleeding phase of the cycle, marking the beginning of a new menstrual cycle.

Role of Hormones

  • The menstrual cycle is regulated by various hormones, including oestrogen, progesterone, FSH, LH, and GnRH.
  • These hormones interact in a complex feedback loop to coordinate the timings of the menstrual cycle.
  • These hormones also contribute to the physical and emotional symptoms associated with different stages of the cycle.