Three layers comprise the uterine wall:

The endometrium is a specialized mucosa that undergoes significant changes throughout the menstrual cycle.

Functional Layer (or stratum functionalis) – the upper two-thirds of the mucosa, which contains glands and is shed during menstruation. It is composed of the simple columnar epithelium, endometrial stroma, and uterine glands.

The Basal Layer (or stratum basalis) is the lowest third of the mucosa that regenerates the functional layer and is maintained during menstruation.