4. Ovarian and Menstrual cycles

4.2. Uterine (Endometrial) Cycle

1.1      Overview

§  The menstrual cycle describes the 28-day cycle of endometrial buildup and sloughing in response to ovarian hormones.

§  Three phases:

1.     Proliferative: proliferation of endometrium and increase in blood vessels (spiral arteries)

2.     Secretory: development of endometrium — thick, vascular, spongy — in preparation for the embryo

3.     Menstrual: constriction of spiral arteries cell death and sloughing of layer of endometrium. Bleeding phase

§  Changes in the endometrium follow changes in the follicles of the ovaries.

1.2      Menstrual Phase (Day 1–5).

  • Shedding of functional layer of endometrium.
  • Occurs as a result of the fall in estrogen and progesterone when the corpus luteum degenerates
  • Arteries in the endometrium constrict, cells in the stratum functionale die, and this region is sloughed.

1.3      Proliferative Phase (Day 6–14)

  • Estrogen → endometrial thickening, cell proliferation.
  • Occurs while ovary is in the follicular phase
  • Increasing levels of estrogen stimulate the growth (cell proliferation ) of the stratum functionale of the endometrium leading to endometrial thickening.
  • The endometrium also becomes more vascular and develops LH receptors.

1.4      Secretory Phase (Day 15–28)

  • Occurs while the ovaries are in the luteal phase
  • Secretion of progesterone stimulates the development of uterine glands, which store glycogen.
    • Progesterone → glandular secretions supportive of implantation.
  • The endometrium also becomes even thicker and more vascular.
  • Endometrium is prepared to nourish a growing embryo if the oocyte is fertilized.

Disorders of the Menstrual Cycle

1 Amenorrhea

  • Primary: no menarche by age 15
  • Secondary: absence for ≥3 months after established cycles
    Causes: PCOS, hyperprolactinemia, thyroid disease, pregnancy.

2 Dysmenorrhea

  • Painful menstruation
  • Primary (prostaglandin-related)
  • Secondary (endometriosis, fibroids)

3 Abnormal Uterine Bleeding (AUB)

  • Heavy or irregular bleeding
  • PALM-COEIN classification