The uterus is made up of an external layer of smooth muscle called the myometrium, and an internal layer called the endometrium.

The endometrium has three layers: stratum compactum, stratum spongiosum (which make up the stratum functionalis) and stratum basalis.

The Stratum compactum and stratum spongialis develop into the stratum functionalis during the first half of the menstrual cycle (proliferative phase)

The wall of the uterus changes during the menstrual cycle, as shown diagramatically here.

Proliferative Phase

In the proliferative phase, facilitated by FSH, the endometrium thickens, connective tissue is renewed, along with glandular structures and ehlicrine arteries. Oestrogen causes the endometrial stroma to become deep and richly vascularised.

Simple tubular glands in the stratum functionalis open out onto the surface, and the endometrium thickens.

Can you recognise the lumen, stratum compactum, stratum spongiosum stratum basalis and myometrium in this photograph?

Secretory Phase

In the secretory phase, facilitated by LH, the endometrial glands become cork-screw shaped, and filled with glycogen. They secrete a glycogen rich secretion during the secretory phase (after ovulation).

You should be able to recognise the glands, and glycogen secretions in this high magnification photo of a secretory phase uterus.

Menses

Decreased levels of LH and progesterone result in the menstrual phase, or menses. During menses (shedding of the uterine lining, which occurs if the egg is not fertilised) the spiral arterioles in the stratum functionalis layer contract, resulting in ischaemia, and degeneration of the functionalis layer. The arteries rupture, and the rapid blood flow dislodges the necrotic functional layer, which is lost. (The basal layer is unaffected, because it is supplied by straight arteries).

You should be able to recognise the lumen, degenerating endometrium, and areas of blood leakage in this photo.