Layers of the chorion laeve

The layers of the chorion laeve from the fetal to the maternal side are as follows (Fig. 3.5):

1 Amnionic epithelium. It is a single cuboideal epithelium secreting and resorbing the amnionic fluid and involved in removal of carbon dioxide and pH regulation.

2 Amnionic mesoderm. It is a thin layer of connective tissue separated from the amnionic epithelium by a basement membrane.

3 Chorionic mesoderm. This second layer of connective tissue is separated from the amnionic mesoderm by slender, fluid-filled clefts. It is continuous with the connective tissue of the chorionic plate.

4 Extravillous trophoblast of the fetal membranes. This specific type of extravillous tropohblast does not display invasive properties and is separated from the chorionic mesoderm by another basement membrane.

Amnionic epithelium

(resting on a basement membrane)

Amnionic mesoderm (separated from the amnionic mesoderm by slender, fluid-filled clefts)

Chorionic mesoderm (separated from extravillous trophoblast by a basement membrane)

Extravillous trophoblast - (embedded in self-secreted matrix-type fibrinoid)

Decidua capsularis (decidualized endometrial stroma)

Fig. 3.5 Layers of the fetal membranes. The amnionic epithelium is a simple epithelium that secretes and resorbs the amnionic fluid. The two layers of connective tissues (amnionic and chorionic mesoderm) are separated by fluid-filled clefts. The extravillous trophoblast of the fetal membranes displays a non-invasive phenotype and is embedded in a self-secreted matrix, termed matrix-type fibrinoid. Finally, on the maternal side the fetal membranes are covered by capsular decidua of maternal origin.

5 Capsular decidua. This layer of maternal cells is directly attached to the extravillous trophoblast. At the end of the implantation process, the decidua closes again over the developing embryo, generating the capsular decidua. During the early second trimester, the capsular decidua fuses with the opposite wall of the uterus causing obliteration of the uterine cavity.

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