This slightly higher magnification view of the stratum functionale shows essentially the same characteristics of the glands (Gl) described above; it also shows other modifications that occur during the secretory stage. 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 stage 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 stage, 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 stage. These modified stromal cells, called decidual cells, play a role in implantation.
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