Explain the roles of follicle-stimulating hormone (FSH), luteinising hormone (LH), oestrogen and progesterone in controlling the menstrual cycle

Sourav PanNovember 3, 2024

Answered

The menstrual cycle is a complex interplay of hormones that regulate the physiological changes in the female reproductive system, facilitating ovulation and preparing the body for potential pregnancy. The key hormones involved in this process are follicle-stimulating hormone (FSH), luteinizing hormone (LH), estrogen, and progesterone. Here’s a detailed explanation of their roles:

1. Follicle-Stimulating Hormone (FSH)

• Source: FSH is produced and released by the anterior pituitary gland in response to signals from gonadotropin-releasing hormone (GnRH) from the hypothalamus.
• Role in the Menstrual Cycle:
  • Follicle Development: FSH stimulates the growth and maturation of ovarian follicles during the follicular phase of the menstrual cycle. Each follicle contains an immature egg (oocyte) that will develop under the influence of FSH.
  • Estrogen Production: As the follicles mature, they produce estrogen, which further influences the menstrual cycle and prepares the uterine lining for potential implantation.

2. Luteinizing Hormone (LH)

• Source: Like FSH, LH is also released by the anterior pituitary gland, triggered by a surge in GnRH.
• Role in the Menstrual Cycle:
  • Ovulation Trigger: The surge in LH levels occurs around day 14 of a typical 28-day cycle and is responsible for triggering ovulation, which is the release of a mature egg from the dominant follicle.
  • Corpus Luteum Formation: After ovulation, LH promotes the transformation of the ruptured follicle into the corpus luteum, which secretes progesterone and some estrogen.

3. Estrogen

• Source: Estrogen is primarily produced by developing ovarian follicles and later by the corpus luteum.
• Role in the Menstrual Cycle:
  • Uterine Lining Growth: Estrogen stimulates the thickening and vascularization of the endometrium (uterine lining) during the follicular phase, preparing it for potential implantation of a fertilized egg.
  • Feedback Mechanism: High levels of estrogen provide positive feedback to stimulate a surge in LH just before ovulation. Additionally, estrogen inhibits FSH production to prevent multiple follicles from maturing simultaneously.

4. Progesterone

• Source: Progesterone is produced by the corpus luteum after ovulation.
• Role in the Menstrual Cycle:
  • Endometrial Maintenance: Progesterone prepares and maintains the endometrium for possible implantation of a fertilized egg. It promotes further thickening of the uterine lining and secretion of nutrients to support an embryo if pregnancy occurs.
  • Inhibition of Further Ovulation: Progesterone exerts negative feedback on both FSH and LH production, preventing further ovulation during this phase. If fertilization does not occur, progesterone levels drop, leading to menstruation as the uterine lining sheds.

Summary of Interactions

• The menstrual cycle consists of several phases:
  • In the follicular phase, FSH stimulates follicle development and estrogen production.
  • The peak in estrogen leads to an LH surge that triggers ovulation.
  • Following ovulation, during the luteal phase, progesterone maintains the uterine lining while inhibiting further follicular development.

If fertilization does not occur, progesterone levels decline, leading to menstruation and resetting the cycle as FSH levels begin to rise again.