Survey of implanted blastocyst (human, ca. 3 weeks-old embryo) and detail of advanced stage of decidua cells (human, mid pregnancy)

Stain: Hematoxylin-eosin (A, left) and Azan (B, right). (A) Left: section through a slightly damaged implantation site shows at (1) the uterine lumen and (2) the decidua capsularis while at (3) several uterine glands are visible. At arrow (4) the amniotic cavity, (5) points to embryonic shield and (6) a collapsed yolk sac. The large exocoelom (extraembryonic coelom, 7) is partly distorted and hemorrhagic. (8) indicates secondary villi with cores of mesoderm. (9) are lacunae due to erosion of the endometrial blood vessels by the syncytiotrophoblast cells (STCs). A deciduous endometrium (decidua basalis) is present at (10). (B) Right: a sample of a deciduous endometrium consisting of transformed stromal cells with one up to three nuclei in larger, polygonal and fine filamentous cytoplasms. In between darker-stained NK- and T- lymphocytes are often interspersed. The decidua cells (10) accumulate glycogen, lipids, contain vimentin intermediate filaments (stromal cells from mesenchymal origin) and produce various secretion products such as insulin-like growth factor, prolactin etc. and are involved in the remodelling of the stromal extracellular matrix in order to modulate the degradative activity of the trophoblast cells. (11) point to capillaries and (12) to fibrinoid deposit.