After the stratum functionale (SF) is sloughed off, resurfacing of the raw tissue occurs. The epithelial resurfacing comes from the glands that remain in the stratum basale (SB). The gland epithelium simply proliferates and grows over the surface. This figure shows the endometrium as it appears when resurfacing is complete. The area inscribed in the upper small rectangle is shown at higher magnification in the inset on the right. Note the simple columnar epithelium (SEp) that covers the endometrial surface and its similarity to the glandular epithelium (Gl). The endometrium is relatively thin at this phase and over half of it consists of the stratum basale. The area inscribed by the lower small rectangle, located in the region of the stratum basale, is shown at higher magnification in the inset in figure below. The glandular epithelium of the deep portion of the glands is similar to that of the endometrial surface. Below the endometrium is the myometrium (M), in which a number of large blood vessels (BV) are present.
Endometrium, proliferative phase, uterus, human, H&E ×25; inset ×120.
Under the influence of estrogen, the various components of the endometrium proliferate (proliferative phase), so that the total thickness of the endometrium is increased. As shown in this figure, the endometrial glands (Gl) become rather long and follow a fairly straight course within the stratum functionale (SF) to reach the surface. The stratum basale (SB) remains essentially unaffected by the estrogen and appears much the same as in above figure. In this figure, the stratum functionale (SF), on the other hand, has increased in thickness and constitutes about four fifths of the endometrial thickness.
BV, blood vessels Gl, endometrial glands M, myometrium SB, stratum basale SEp, surface epithelium SF, stratum functionale KEY
After estrogen brings about the uterine events designated the proliferative phase another hormone, progesterone, influences additional uterine changes that constitute the secretory phase of the uterine cycle. This hormone brings the endometrium to a state of readiness for implantation, and as a consequence of its actions, the thickness of the endometrium increases further. There are conspicuous changes in the glands, primarily in the stratum functionale, where the glands take on a more pronounced corkscrew shape and secrete mucus that accumulates in sacculations along their length. The vasculature of the endometrium also proliferates and degenerates in each menstrual cycle. Radial arteries enter the stratum basale of the endometrium from the myometrium and give rise to small, straight arteries that supply the stratum basale and continue into the endometrium to become the highly coiled spiral arteries. Arterioles derived from the spiral arteries supply the stratum functionale. The distal portion of the spiral arteries and the arterioles are sloughed with the stratum functionale during menstruation. Alternating contraction and relaxation of the basal portions of the spiral arteries prevent excessive blood loss during menstruation.
Uterus, human, H&E ×25.