Endometrium

Uterus

uterus histology uterus histology


Menstrual cycle and the endometrium

menstrual cycle and the endometrium
Endometrium
The endometrium is divided into the basalis and functionalis. The basalis is a thin layer of endometrium attached to the underlying myometrium and stays constant over the menstrual cycle. The functionalis lies ontop of the basalis and changes in response to estrogen levels, it sheds during menstration when estrogen levels fall, and grows when estrogen levels increase.

Proliferation phase
At the end of menstration the endometrium is lined by a thin basal endometrium and a thin functionalis endometrium. At the start of the proliferative phase, the functional endometrium starts to thicken and there is glandular, stromal and vascular growth. During this time the glands are unifrom and with regular wide space in between them.
Histology
  1. Wide and regular space between glands
  2. Glands are uniform
      Tubular glands, can be mildly dilated
      The glands are lined with cuboidal or low-columnar epithelium / cells which is pseudostratified
      The nuclei is oval to rounded and basally placed. Small nucleoli might be seen.
      Mitotic figures are found in the glands
      Some epithelial cells might be ciliated apically.
    After the 8th day, the epithelium becomes more stratified and more mitotic figures are apparent. In the last days of the proliferative phase the glands might start to become more irregular, and subnuclear vacuoles might appear.
  3. Stroma is densely cellular
      Stromal cells are small with oval and hyperchromatic nuclei
      Cell borders cannot be seen
      Mitotic figures might be seen (though not as many as in the glands)
      A few thin-walled vessel are seen
      Lymphoid aggrigates might be seen
    In the last days of the proliferative phase, you start to see edema in the stroma.

Secretory phase
During the secretory phase the endometrium continues to thicken and develop. The secretory phase is divided into:
  1. The early secretory phase (day 16-18)
      Glands still have a tubular appearance and some mitotic activity. Subnuclear vacuoles start to appear, most often first in the midzone of the functionalis. In the end of this phase, subnuclear vacuoles are seen in almost all glandular cells. One can assume that ovulation has occurred if >50% of the glands have at least 50% of the cells with subnuclear vacuoles.
      Stroma is identical to late-proliferative phase stroma.
  2. The mid-secretory phase (19-23)
      Glandular secreation increases during this phase, seen in the glandular lumina, and cytoplasmic vacules move to become supranuclear.
        Glands become angular
        Mitotic activity disappears
        Stromal edema increases, and will be most prominant in the mid-zone
        Spiral arteries appear, and stromal cells surrounding them have eosinophilic cytoplasm. these cells later become predecidual cells.
  3. The late secretory phase (24-28)
      Now glands become serrated and tightly packed and predecidual stroma changes are more evident. Sometimes the precidual cells have a spindle cell appearance or even signet-ring cell morphology. Lymphocytes are seen infiltrating the stroma and even neutrophils may be seen.

Menstrual phase
  1. Endometrial glands are serrated and start to collaps
  2. Endometrial stroma is compact and starts to collaps into tighty aggregated balls with hyperchromatic nuclei, called "blue balls"
  3. Other features: Necrotic debris, neutrophils, interstitial hemorrhage, fibrin, apoptotic debris.
  4. The glands become tightly packed as the stroma breaks down, even assuming micropapillary morphology (called papillary syncytial metaplasia).