Summary of GCSE Biology - The Menstrual Cycle & Puberty #60

Main Ideas and Concepts

• Puberty:
  • Defined as the period when adolescents develop secondary sexual characteristics.
  • In men, this includes the development of facial hair, while in women, it includes breast development.
  • Triggered by reproductive hormones: testosterone in men (produced in the testes) and Estrogen in women (produced in the ovaries).
• The Menstrual Cycle:
  • The average Menstrual Cycle lasts about 28 days but can vary among individuals.
  • The cycle consists of four stages, with hormonal interactions playing a crucial role in each.
• Stages of the Menstrual Cycle:
  • Stage 1: Menstruation (Days 1-4)
    • Involves bleeding due to the breakdown of the uterine lining.
  • Stage 2: Uterine Lining Building (Days 5-14)
    • The uterine lining thickens and becomes spongy, preparing for a potential fertilized egg.
  • Stage 3: Ovulation (Day 14)
    • The egg is released from one of the ovaries.
  • Stage 4: Maintenance of Uterine Lining (Days 15-28)
    • If no fertilization occurs, the uterine lining breaks down, restarting the cycle. If fertilization occurs, the cycle stops as the embryo develops.
• Hormones Involved:
  • Estrogen: Produced in the ovaries; stimulates the growth of the uterine lining.
  • Progesterone: Also produced in the ovaries; maintains the uterine lining.
  • Luteinizing Hormone (LH): Produced in the pituitary gland; triggers ovulation.
  • Follicle Stimulating Hormone (FSH): Also produced in the pituitary gland; stimulates egg maturation.
• Hormonal Interactions:
  • FSH stimulates the ovaries to produce Estrogen.
  • Increased Estrogen levels inhibit FSH production (negative feedback).
  • High Estrogen levels stimulate LH release, leading to ovulation.
  • Progesterone inhibits both LH and FSH, preventing the restart of the Menstrual Cycle if pregnancy occurs.

Methodology/Instructions

Understanding the Menstrual Cycle involves recognizing the stages and hormonal interactions:

• Track the cycle: Note the duration and changes in the uterine lining.
• Monitor hormone levels: Recognize how FSH, LH, Estrogen, and Progesterone interact during each stage.

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