Hormonal Cycle

Introduction to the Hormonal Cycle

• Discussion about the hormonal cycle or the changes in hormone levels as a woman progresses through the ovarian, uterine, or menstrual reproductive cycle.

Graphing the Hormonal Cycle

• Creating a graph to represent the hormonal cycle.

  • Title of the Graph: "The Female Hormone Cycle".

  • Axes:

  • Y-Axis (Vertical): Concentration of Hormones in brackets, indicating units in nanograms per milliliter (ng/mL).

  • X-Axis (Horizontal): Time, measured in days.

  • Basic Concept: The graph aims to show how female hormones and their concentrations change over time as the cycle progresses.

Ovarian Cycle Phases

• The ovarian cycle can be divided into:

  • Follicular Phase: Development of the follicle.

  • Luteal Phase: Persistence of the corpus luteum.

  • Ovulation: The release of the egg occurs fleetingly between the follicular and luteal phases.

Hypothalamic-Pituitary Target Axis

• Overview of the hypothalamic-pituitary-gonadal (HPG) axis:

  • The hypothalamus communicates with the anterior pituitary gland.

  • Important hormones involved:

  • GnRH (Gonadotropin-Releasing Hormone)

  • LH (Luteinizing Hormone)

  • FSH (Follicle Stimulating Hormone)

  • These hormones stimulate the ovary to produce estrogen (estradiol).

Role of the Corpus Luteum

• After ovulation, the corpus luteum produces:

  • Progesterone

  • Estrogen

  • Inhibin

• Importance of these hormones in the female hormone cycle.

Development of Ovarian Follicles

• Stages of follicle development:

  • Primordial Follicle: Contains an egg arrested in prophase of meiosis I (diploid).

  • Primary Follicle: Primordial follicle becomes primary with a single layer of epithelium.

  • Secondary Follicle: Development with multiple layers of granulosa cells forming.

  • Late Secondary Follicle: Many layers, with thecal cells starting to form.

  • Tertiary Follicle (Antral Follicle): Characterized by the presence of fluid-filled cavities and a mature follicle.

  • Graphean Follicle: The mature follicle ready to rupture, leading to ovulation.

Process of Ovulation

• During ovulation:

  • The egg completes meiosis I and enters metaphase of meiosis II.

  • The follicle ruptures, releasing the egg and the surrounding structures (corona radiata and zona pellucida).

  • The ruptured follicle transforms into the corpus hemorrhagicum and eventually into a corpus luteum.

  • If not fertilized, it degenerates to the corpus albicans.

Hormonal Changes in the Menstrual Cycle

• Estrogen:

  • Levels are low at the beginning of the follicular phase.

  • Rise as granulosa cells divide, peaking around day 14 (ovulation).

  • Post-ovulation drop due to follicle trauma but rises again with corpus luteum activity.

  • If fertilization occurs, hCG rescues corpus luteum, maintaining estrogen levels; if not, levels decline.

• FSH (Follicle Stimulating Hormone):

  • Stimulates granulosa cells for estrogen production.

  • Low estrogen suppresses GnRH; optimal levels stimulate it.

  • Peaks around day 14, leading to positive feedback with increased estrogen levels.

  • Inhibin from corpus luteum results in decreased FSH production post-ovulation.

• LH (Luteinizing Hormone):

  • Peaks at day 14, resulting in ovulation.

  • Triggers rupture of the follicle by affecting ovarian blood vessels and thecal cells.

  • Followed by suppression due to high estrogen and inhibin levels.

• Progesterone:

  • Low until corpus luteum formation post-ovulation.

  • Rapid increase after ovulation; levels drop if no fertilization occurs.

  • High levels suppress FSH and LH to prevent new follicle development during an active cycle.

Connections with the Uterine Cycle and Implications

• The hormonal changes directly influence the uterine cycle (menstrual cycle).

• Establishes the environment for potential fertilization and subsequent implantation of an embryo.

• Highlights the interplay between hormones to prevent concurrent follicle development and ensure reproductive success.