This view of the endometrium in the secretory phase shows the stratum functionale (SF), the stratum basale (SB), and, in the lower left of the photomicrograph, a small amount of the myometrium (M). The uterine glands have been cut in a plane that is close to their long axes, and one gland (arrow) is seen opening at the uterine surface. Except for a few glands near the center of the figure that resemble those of the proliferative phase, most of the glands (Gl) in this figure, including those that are labeled, show numerous shallow sacculations that give the profile of the glandular epithelium a serrated appearance. This is one of the distinctive features of the secretory phase. It is seen most advantageously in areas where the plane of section is close to the long axis of the gland. In contrast to the characteristic sinuous course of the glands in the stratum functionale, glands of the stratum basale more closely resemble those in the proliferative phase. They are not oriented in any noticeable relationship to the uterine surface, and many of their long profiles are even parallel to the plane of the surface.
Endometrium, secretory phase, uterus, human, H&E ×30; inset ×120.
This slightly higher-magnification view of the stratum functionale shows essentially the same characteristics of the endometrial glands (Gl) described above; it also shows other modifications that occur during the secretory phase. One of these is that the endometrium becomes edematous. The increase in endometrial thickness because of edema is reflected by the presence of empty spaces between cells and other formed elements. Thus, many areas of this figure, especially the area within and near the rectangle, show histologic signs of edema.
In addition, in this phase the glandular epithelial cells begin to secrete a mucoid fluid that is rich in glycogen. This product is secreted into the lumen of the glands, causing them to dilate. Typically, the glands of the secretory  endometrium are more dilated than those of the proliferative endometrium.
The rectangle in this figure highlights two glands that are shown at higher magnification in the inset. Each of these glands contains some substance within the lumen. The mucoid character of the substance within one of the glands can be surmised from its blue staining. Although not evident in routine H&E paraffin sections, the epithelial cells also contain glycogen during the secretory phase and as mentioned above, this becomes part of the secretion. The arrowheads indicate stromal cells; some of these cells undergo enlargement late in the secretory phase. These modified stromal cells, called decidual cells, play a role in implantation.
Gl, endometrial glands M, myometrium SB, stratum basale SF, stratum functionale arrow, glandular opening at uterine surface arrowheads, stromal cells KEY
The cervix is the narrow or constricted inferior portion of the uterus, part of which projects into the vagina. The cervical canal traverses the cervix and provides a channel connecting the vagina and the uterine cavity. The structure of the cervix resembles the rest of the uterus in that it consists of a mucosa (endometrium) and a myometrium. There are, however, some important differences in the mucosa. The endometrium of the cervix does not undergo the cyclical growth and loss of tissue that is characteristic of the body and fundus of the uterus. Rather, the amount and character of the mucous secretion of its simple columnar epithelium vary at different times in the uterine cycle under the influence of the ovarian hormones. At midcycle, there is a 10-fold increase in the amount of mucus produced; this mucus is less viscous and provides a favorable environment for sperm migration. At other times in the cycle, the mucus restricts the passage of sperm into the uterus. The myometrium forms the major thickness of the cervix. It consists of interweaving bundles of smooth muscle cells in an extensive, continuous network of fibrous connective tissue.
Cervix, uterus, human, H&E ×15.