Uterine Cycle Flashcards

Uterine Cycle (Menstrual Cycle)

• Focuses on what the uterus, specifically the endometrium, is doing during a 28-day cycle.

• The perimetrium and myometrium do not change significantly during this cycle, but the endometrium does.

Three Phases of the Uterine Cycle

• Menstrual Phase:

  • Days 1-5 (approximately).

  • May vary in length (e.g., 3-7 days).

  • The stratum functionalis of the endometrium detaches from the uterine wall and is shed.

• Proliferative Phase:

  • Days 6-14 (approximately).

  • Occurs before ovulation.

  • The stratum functionalis rebuilds.

  • Blood vessels increase, and glands begin to appear.

  • Estrogen increases, thinning cervical mucus to aid sperm passage.

• Secretory Phase:

  • Days 15-28.

  • The stratum functionalis is at its thickest.

  • Prepares for potential embryo implantation.

  • Ovulation occurs around day 14; it takes about a week for the oocyte to travel from the fallopian tubes to the endometrium.

  • If fertilized, the oocyte will embed around day 20-21.

  • Glands secrete nutrients into the uterine lumen.

  • Mucus thickens to block further sperm entry.

Endometrial Layers

• Stratum Functionalis: The layer that is shed during menstruation and rebuilt during the cycle.

• Stratum Basalis (Stratum basale): The basal layer that remains constant.

Hormonal Influence

• Progesterone:

  • Helps in the development of the endometrial layer.

  • Secreted by the corpus luteum after ovulation.

  • Drives the transition from the proliferative to the secretory phase.

• Estrogen and Progesterone Drop:

  • When these hormone levels decrease, the endometrial lining is lost, and the cycle begins again.

Fertilization and Implantation

• Ovulation occurs, and fertilization ideally takes place in the ampulla.

• The fertilized egg divides as it moves along the fallopian tube.

• Around day 6 after ovulation, the blastocyst implants into the endometrial layer.

• Example: If ovulation occurs on day 10, implantation occurs around day 16.

Purpose of the Uterine Cycle

• To prepare the endometrial lining for the implantation of a fertilized egg.

• If fertilization does not occur, the lining is shed, and the cycle restarts.