Hormones + cycles

Hormonal control of the ovarian cycle: follicular phase

  1. During the follicular phase, FSH helps follicles grow.

  2. LH helps granulosa and theca cells make estrogen.

  3. The dominant follicle makes the most estrogen and sends negative feedback to stop other follicles from growing.


    Hormonal control of the ovarian cycle: ovulation

    1. The dominant follicle makes a lot of estrogen, causing positive feedback and a surge in FSH and LH (LH surge signals ovulation).

    2. The LH surge helps the primary oocyte finish meiosis and activates enzymes to break the ovary wall.

    3. Fluid pressure pushes the oocyte out of the ovary.

      Hormonal control of the ovarian cycle: luteal phase


      LH turns the empty follicle into the corpus luteum.

    4. The corpus luteum makes progesterone, which sends negative feedback and helps prepare for pregnancy.

    5. If there’s no pregnancy, the corpus luteum breaks down.

The menstrual cycle

Menses Phase (around 5 days):

  • Happens when progesterone drops at the end of the luteal phase.

  • Hormone levels (progesterone, FSH, LH) are low.

  • The lining of the uterus (stratum functionalis) sheds and exits as menstrual flow.

Proliferative Phase:

  • The uterine lining starts to regrow.

  • Estrogen from growing follicles (granulosa and theca cells) stimulates this growth.

  • Ends with the LH surge and ovulation (around day 14).

Secretory Phase:

  • Estrogen helps move the egg through the uterine tube and reduces vaginal acidity.

  • Progesterone from the corpus luteum thickens the uterine lining.

  • The lining secretes nutrients (glycogen) to support a possible embryo.

  • Spiral arteries bring blood to the thickened lining.

  • If no embryo, estrogen and progesterone levels drop, leading to the next period.