[Biology][Practical-14] Menstrual Cycle Final Review

General Discussion
1

MENSTRUAL CYCLE

  • Day 1 of the menstrual cycle is the first day of the period

  • The hormones that control the menstrual cycle are LH + FSH which are secreted by the pituitary gland and estrogen + progesterone which are secreted by the ovaries

  • The thickness of the endometrium is mediated by the following hormones: estrogen and progesterone

  • Ovulation occurs on the day 14 of the menstrual cycle due to a rise in LH

  • What are the roles of FSH?

  1. follicular growth

  2. triggers estrogen secretion

  • LH results in the formation of the corpus luteum

  • The uterine lining is called endometrium

  • What are the roles of estrogen?

  1. thickening of the uterine lining

  2. inhibition of LH and FSH during most of the cycle

  3. triggers the release of FSH and LH before ovulation

  • What are the roles of progesterone?
  1. thickening of the uterine lining
  2. inhibition of FSH and LH

  • Complete the following:

    • Progesterone and Estrogen cause negative feedback on the Hypothalamus (which releases GnRH) and the Anterior Pituitary (which releases FSH and LH) until day 12-14.

    • Then Estrogen suddenly causes positive feedback to occur on both the Anterior pituitary and the Hypothalamus

  • The 4 steps of the menstrual cycle are:

  1. follicular phase
  2. ovulation
  3. luteal phase
  4. menstruation

  • What happens during the follicular phase?

    • The dominant follicle produces Estrogen, which inhibits FSH and LH during most of the cycle (for around 12-14 days)

    • The Estrogen released by the leading follicle prevents other follicles from developing

    • At the same time, Estrogen causes the uterus to increase in size, together with progesterone

  • During ovulation, LH causes the dominant follicle to rupture and release an egg (a secondary oocyte).

  • During the luteal phase, the ruptured follicle develops into the corpus luteum, which secrets high levels of progesterone and some estrogen.

  • The corpus luteum is only sustained if there is fertilization

  • The corpus luteum degenerates into the corpus albicans which reduces the levels of progesterone and Estrogen and allows the shedding of the endometrial layer

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