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
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?
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.
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.