L4.3.3: Ovarian Cycle

• Phases

  • Follicular Phase
  • Ovulation
  • Luteal Phase
• FOLLICULAR PHASE (1 - 13 days)

  ● Occurs at the first stage of the menstrual cycle; between the first day of menstruation and ovulation.

  ● Follicle

  ○ A sac or pouch-like cavity formed by a group of cells.

  ○ Oocytes surrounded by a layer of Granulosa cells.

  ○ Granulosa Cells: Produces Estrogen, Progesterone, Inhibin
• FOLLICULAR PHASE (1 - 13 days)

  ● As they mature, the follicles secrete increasing amounts of estrogen which causes the egg to mature and be ready for its release through the influence of FSH.

  ○ FSH stimulates follicles to develop

  ○ LH stimulates follicles to mature

  ■ LH peaks pre-ovulatory period for the follicle to easily rupture!
• FOLLICULAR PHASE (1 - 13 days)

  ● Estrogen

  ○ Stimulates crypts in the cervix to produce fertile cervical mucus.

  ● At the end of this phase (14th day—half of the menstrual cycle), ovulation occurs.

  ○ Because the antrum of the Graafian follicle pushes further the egg for it to be released.
• OVULATION (14th day) — MOST FERTILE PERIOD

  ● The release of LH matures the ovum and weakens the wall of the follicle in the ovary, causing the fully developed follicle to release its secondary oocyte.

  ● After being released from the ovary, the ovum is swept into the fallopian tube.

  ○ The ovum will wait in the fallopian tube for 24 hours for the sperm to penetrate.
• LUTEAL PHASE (15 - 28 days)

  ● Lasts about 14 days!

  ● Transformation from a follicle to a corpus.

  Graafian Follicle → Corpus Luteum → Corpus Albicans
• LUTEAL PHASE (15 - 28 days)

  ● Development of the corpus luteum

  ○ Solid body formed in an ovary after the ovum has been released into the fallopian tube.

  ○ Trigger the increase of the production of hormones:

  ■ Progesterone hormone: helps the egg to remain viable;

  ■ Estrogen hormone: correlated to the thickening of endometrium.
• LUTEAL PHASE (15 - 28 days)

  ● Lutein Cells

  ○ Replaces the granulosa cells and mainly produces progesterone.
• LUTEAL PHASE (15 - 28 days)

  ● Produces significant amounts of progesterone, which plays a vital role in making the endometrium receptive to implantation of the blastocyst.

  ● High levels of estrogen and progesterone suppress production of FSH and LH that the corpus luteum needs to maintain itself.

  ○ The roles of FSH and LH are finished.

  ○ An example of negative feedback.
• LUTEAL PHASE (15 - 28 days)

  Falling levels of progesterone trigger menstruation and the beginning of the next cycle.

  ○ Fertilization (?)

  ■ if true, the progesterone will rise

  ○ No Fertilization (?)

  ■ If true, the estrogen level will fluctuate.

  ■ Progesterone will lower and trigger menstruation
• LUTEAL PHASE (15 - 28 days)

  Corpus Albicans

  ○ Degenerated form of corpus luteum
• Pro = Before Geste = Pregnancy Rone = Hormone

  Progesterone is a before-pregnancy-hormone