Endometrium - Histology

Histology

The endometrium consists of a single layer of columnar epithelium resting on the stroma, a layer of connective tissue that varies in thickness according to hormonal influences. Simple tubular uterine glands reach from the endometrial surface through to the base of the stroma, which also carries a rich blood supply of spiral arteries. In a woman of reproductive age, two layers of endometrium can be distinguished. These two layers occur only in endometrium lining the cavity of the uterus, not in the lining of the Fallopian tubes:

• The functional layer is adjacent to the uterine cavity. This layer is built up after the end of menstruation during the first part of the previous menstrual cycle. Proliferation is induced by estrogen (follicular phase of menstrual cycle), and later changes in this layer are engendered by progestrone from the corpus luteum (luteal phase). It is adapted to provide an optimum environment for the implantation and growth of the embryo. This layer is completely shed during menstruation.
• The basal layer, adjacent to the myometrium and below the functional layer, is not shed at any time during the menstrual cycle, and from it the functional layer develops.

In the absence of progesterone, the arteries supplying blood to the functional layer constrict, so that cells in that layer become ischaemic and die, leading to menstruation.

It is possible to identify the phase of the menstrual cycle by observing histological differences at each phase:

Chorionic tissue can result in marked endometrial changes, known as an Arias-Stella reaction, that have an appearance similar to cancer. Historically, this change was diagnosed as endometrial cancer and it is important only in so far as it should not be misdiagnosed as cancer.