Ovarian Cycle and Menstrual Cycle Overview

Ovarian Cycle

• Cyclic changes occurring in the ovaries under the influence of FSH and LH hormones produced by the anterior pituitary gland.
• Includes follicle development, ovulation, and corpus luteum formation.

Phases of Ovarian Cycle

• Pre-ovulatory Phase:
  • Gonadotropin-releasing hormone (GnRH) stimulates the anterior pituitary gland to release FSH.
  • FSH aids in follicular development, turning them into Graafian follicles.
  • Follicles become endocrine structures during this phase.
• Ovulatory Phase:
  • GnRH stimulates the anterior pituitary gland to release LH.
  • LH surge causes ovulation, leading to the release of the mature oocyte from the follicle.
• Post-ovulatory Phase:
  • The ruptured follicle transforms into a corpus luteum
  • Corpus luteum secretes progesterone.

Menstrual Cycle

• Defined as the timeframe during which the oocyte matures, is released from the ovary, and travels to the uterine tube.
• Ovarian hormones estrogen and progesterone influence cyclic changes in the endometrium.
• Also known as the endometrial cycle.

Phases of Menstrual Cycle

• Proliferative Phase:
  • Estrogen secreted by granulosa cells controls this phase.
  • Estrogen stimulates the proliferation of endometrial stromal cells, glands, and blood vessels.
• Secretory Phase (Luteal Phase):
  • Progesterone, secreted by the corpus luteum, controls this phase.
  • Progesterone stimulates endometrial glands to secrete mucous.
• Menstrual Phase:
  • This is the bleeding phase where endometrial shedding occurs if fertilization does not take place.
  • Typically lasts between 4 to 5 days.
  • If fertilization does not happen:
    • The corpus luteum degenerates.
    • Estrogen and progesterone levels decrease.
    • The secretory endometrium enters the ischemic phase.
    • Menstruation occurs.
• Ischemic Phase:
  • The endometrium experiences a decline in blood supply due to low progesterone and estrogen levels ultimately resulting in shedding or menstruation.

Fertilization

• Occurs when the sperm fertilizes the egg in the uterine tube.
• If fertilization occurs:
  • The zygote undergoes cleavage and forms a blastocyst.
  • HCG is secreted by the blastocyst and reaches the corpus luteum.
  • HCG maintains the progesterone and estrogen levels secreted by the corpus luteum.
  • The secretory phase continues and prevents menstruation.
  • This ultimately leads to pregnancy.

Ovarian Cycle

• Cyclic changes in the ovaries under the influence of Follicle Stimulating Hormone (FSH) and Luteinizing Hormone (LH) produced by the anterior pituitary gland.
• Includes development of follicles, ovulation, and corpus luteum formation.

Phases of the Ovarian Cycle

• Pre-ovulatory phase: Gonadotropin-releasing hormone (GnRH) from the hypothalamus stimulates the anterior pituitary gland to secrete FSH, which stimulates follicle growth.
• Ovulatory phase: GnRH induces the anterior pituitary gland to secrete LH, triggering ovulation.
• Post-ovulatory phase: The corpus luteum forms and secretes progesterone.

Menstrual Cycle

• Represents the time period during which the oocyte matures, is ovulated, and enters the uterine tubes.
• Cyclic changes in the endometrium are driven by estrogen and progesterone (ovarian hormones).
• The menstrual cycle is also known as the endometrial cycle.

Phases of the Menstrual Cycle

• Proliferative phase: Controlled by estrogen secreted from granulosa cells. Estrogen promotes the proliferation of endometrial stromal cells, glands, and blood vessels.
• Secretory phase (Luteal phase): Controlled by progesterone secreted from the corpus luteum. Progesterone stimulates endometrial glands to secrete mucous secretions.
• Menstrual phase: The bleeding phase. Endometrial shedding occurs if fertilization fails. Typically lasts 4 to 5 days.

Menstruation: Breakdown

• If fertilization does not occur, the corpus luteum degenerates.
• Estrogen and progesterone levels decrease, leading the secretory endometrium to enter the ischemic phase.
• Menstruation commences.

Ischemic Phase

• Occurs due to lack of hormone support as the corpus luteum degenerates.
• The endometrium becomes starved of nutrients and oxygen, leading to ischemia (lack of blood flow).

Fertilization

• If fertilization occurs, the zygote cleaves and blastogenesis (formation of blastocyst) begins.
• The blastocyst implants in the endometrium.
• Human chorionic gonadotropin (hCG) hormone maintains the corpus luteum's production of estrogen and progesterone.
• The luteal phase continues, preventing menstruation. This marks the pregnancy phase.

Ovulation

• The release of a mature egg (oocyte) from the ovary.
• The dominant follicle ruptures, releasing the egg.

After Rupture

• The ruptured follicle transforms into the corpus luteum.
• The corpus luteum produces progesterone.
• Progesterone prepares the uterus for a potential pregnancy.

Explore the intricate changes of the ovarian cycle driven by FSH and LH hormones. This quiz covers the phases of the ovarian cycle, including follicle development, ovulation, and the role of the corpus luteum, as well as the menstrual cycle timeline. Test your knowledge and understanding of female reproductive physiology.