Reeproductive extended response

• Interaction between oestrogen, progesterone, luteinising hormone and follicle-stimulating hormone in the female reproductive system

  Follicle-stimulating hormone (FSH):

  • Produced by: Anterior pituitary gland
  • Role: Initiates the growth and maturation of ovarian follicles
  • Interaction:
  • Early Follicular Phase: FSH levels increase slightly, stimulating the development of several follicles
  • Mid-follicular phase: As the FSH level decreases, usually only one follicle continues to develop and begins secreting oestrogen

  Oestrogen:

  • Produced by: Growing ovarian follicles
  • Role: Regulates the menstrual cycle and prepares the endometrium for potential implantation; also affects breast tissue
  • Interaction:
  • Follicular Phase: Low oestrogen levels at the start cause the endometrium to break down and shed, leading to menstrual bleeding
  • Mid Follicular Phase: The developing follicle produces increasing levels of oestrogen, promoting the thickening of the endometrium
  • Late Follicular Phase: High oestrogen levels stimulate a surge in LH and FSH

  Luteinising Hormone (LH):

  • Produced by: Anterior pituitary gland
  • Role: Triggers ovulation and the formation of the corpus luteum
  • Interaction:
  • Late Follicular Phase: High oestrogen levels cause an LH surge, leading to ovulation
  • Ovulation: LH surge stimulates the release of the egg
  • Post-Ovulation: LH supports the corpus luteum formation from the ruptured follicle

  Progesterone:

  • Produced by: Corpus luteum
  • Role: Prepares and maintains the endometrium for implantation and pregnancy
  • Interaction:
  • Luteal Phase: Progesterone levels rise, promoting further thickening of the endometrium. Oestrogen levels are also high during this phase
  • If No Pregnancy: Decreased levels of progesterone and oestrogen lead to the breakdown of the endometrium and menstrual bleeding
  • If Pregnancy Occurs: The corpus luteum continues to produce progesterone to maintain the pregnancy

  Feedback Mechanisms:

  1. Negative Feedback:

  • Follicular Phase: Low levels of oestrogen and progesterone inhibit FSH
  • Luteal Phase: High levels of progesterone and oestrogen inhibit FSH and LH

  2. Positive Feedback:

  • Late Follicular Phase: High oestrogen levels stimulate an LH surge

  Phases of the Menstrual Cycle:

  1. Follicular Phase:

  • FSH stimulates the growth of multiple follicles, leading to increased oestrogen production
  • Rising oestrogen levels initially inhibit FSH but later cause an LH surge

  2. Ovulation:

  • The LH surge triggers the release of a mature egg
  • During the surge, oestrogen levels decrease while progesterone levels begin to increase

  3. Luteal Phase:

  • LH maintains the corpus luteum, which secretes progesterone and oestrogen
  • High progesterone prepares the endometrium and inhibits further FSH and LH secretion

  4. Menstruation:

  • If pregnancy does not occur, the corpus luteum degenerates
  • Decreased progesterone and oestrogen levels lead to endometrial shedding and the start of a new cycle
  • If pregnancy occurs, the corpus luteum continues functioning, maintaining early pregnancy