Menses Phase

The menstrual cycle starts with the menstrual phase, with its first day considered Day 1 of the cycle.

This phase usually lasts for 1 to 5 days and is characterized by the degeneration and shedding of the endometrial functional layer, or stratum functionalis.

The lack of fertilization leads to degeneration of the corpus luteum, decreasing the circulating levels of estrogen and progesterone.

Their decreased levels trigger the release of prostaglandins, which cause the uterine spiral arterioles to constrict.

Deprived of oxygen, the secretory glands and other tissues in the stratum functionalis start to break down.

The weakened arterial walls eventually rupture, disrupting the tissue organization of the stratum functionalis.

Blood cells and deteriorating tissues are then shed through the vagina in a process known as menstruation.

The resulting vaginal discharge consists of a mixture of blood, tissue fluid, mucus, and epithelial cells shed from the endometrium.

As a result, the endometrium thins to approximately 2 to 5 mm, with only the stratum basalis layer remaining.