In order to determine the maternal changes contributing to the formation of the chorioallantoic and yolk-sac placentas, rat gestation sites were examined by light and electron microscopy on days 7 through 10 of pregnancy. On day 7, the implantation chamber showed different compartments and contained the blastocyst in the antimesometrial chamber. The epithelial lining of the implantation chamber disappeared at the antimesometrial chamber, transformed into disintegrated cells in the mesometrial chamber, and showed signs of the programmed cell death in the decidual crypt. On day 8, the mesometrial chamber lumen contained red blood cells and it was continuous with subepithelial sinusoids. The endothelial cells lining the mesometrial sinusoids also showed some characteristics of the sprouting type angiogenesis such as hypertrophy and cell proliferation. While the yolk-sac placental circulation was more obvious with participation of the giant trophoblasts at the antimesometrial pole of the conceptus on day 9, the antimesometrial cells showed autophagic degeneration after the formation of the chorioallantoic placenta on day 10. The contribution of the regional cell death and angiogenesis to form both of the two placentas are discussed.

Summary: Very complex cellular events take place at the morphological and molecular levels both in the maternal and embryonic sites during blastocyst implantation. Although the morphological alterations in the gestational stages of the implantation site are well-known, mechanisms of the interaction between blastocyst and endometrial epithelium (apposition and adhesion stages) and penetration of the blastocyst into the endometrium have not yet been fully described. Therefore the present study was designed to determine these events morphologically throughout the implantational stages.To do this the endometrial tissues containing implantation sites from pregnant rats were taken 5 and 8 days after fertilization. In addition, non-pregnant rat endometrial tissues were also obtained in order to use as control. Tissues were processed for light and electron microscopy. Semi-thin and ultra-thin sections were stained using appropriate staining methods, and were evaluated under light and electron microscope.In the present study, interaction between trophoblast and luminal epithelium, penetration of the blastocyst into the endometrium, differentiation of germinal layers in the blastocyst and tissue alterations such as decidualization in the maternal site have been demonstrated morphologically.In condusion, while blastocyst was implanted into the endometrium, distinct morphological changes occurred both in maternal and embryonic sites. The following stages of implantation were the development of germinal layers in the embryo and morphological changes in the maternal site leading to the placentation.

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Summary: In this study carried out on the development of arteriovenous anastomoses (AVAs) in Rattus norvegicus species, the fetus was followed up 10 days after post coitum (pc). The sections obtained from the fetuses of 10-20-day rats were subjected to the usual processes for examination under the light microscope. Various staining processes were applied on the preparations and the simple and glomus types of AVAs determined in the mesenchyme of fetuses observed to birth every day. The regions with AVAs were then photographed by photomicroscopy and evaluated. From the 10-day embryo to birth, an increase in the smooth muscles in the wall structure of simple anastomoses was observed. It was however very difficult to follow up this increase in glomus anastomoses because the wall structure is more complicated. Their morphology was examined and compared with that in literature.

Some observations on arteriovenous anastomosis (AVA) morphogenesis of rats were considered in this investigation. Interesting typical glomus anastomoses observed under light microscopy were determined by photography before evaluation. AVAs in the skin and mesentery were compared with those reported in morphological studies in the literature. Most of the glomus anastomoses were determined to be in conformity with those in the studies reported. Some resembled simple shunts and others complex glomus anastomoses. It is suggested that the existence of various types of anastomoses of rat fetuses during development is dependent on blood flow.