decidua basalis
decidua serotina

It surrounds the embryo together with decidua basalis.

Thus the placenta develops from the chorion frondosum and the decidua basalis.

There is absence of the decidua basalis and incomplete development of the Nitabuch's layer.

Endometrium on the opposite side to the decidua basalis is the decidua parietalis.

The cytotrophoblastic shell firmly secures the placenta to the mother's endometrium called the decidua basalis.

Decidua basalis - This is the part of the decidua which is located basalolateral to the embryo after implantation.

In human development, the cotyledons are the approximately 15-30 separations of the decidua basalis of the placenta, separated by placental septa.

The endometrium (from the mother) over the chorion frondosum (this part of the endometrium is called the decidua basalis) forms the decidual plate.

That part of the decidua that interacts with the trophoblast is the decidua basalis (also called decidua placentalis).

Trauma, hypertension, or coagulopathy contributes to the avulsion of the anchoring placental villi from the expanding lower uterine segment, which in turn, leads to bleeding into the decidua basalis.

Also, there is the decidua capsularis, which grows over the embryo on the luminal side, enclosing it into the endometrium and surrounding the embryo together with decidua basalis.

On the other hand, the villi at the embryonic pole, which is in contact with the decidua basalis, increase greatly in size and complexity, and hence this part is named the chorion frondosum.

The hemorrhage that gets into the decidua basalis ultimately splits the decidua, and the haematoma may remain within the decidua or may extravasate into the myometrium (the muscular wall of the uterus).

The whole placenta, after dissection from the uterus in mid-gestation, contains both a fetal component (the placenta proper, consisting of the labyrinth, spongiotrophoblast and giant cell layers) and a maternal component (the decidua basalis, as well as maternal blood vessels).

The placenta functions as a fetomaternal organ with two components: the fetal placenta (Chorion frondosum), which develops from the same blastocyst that form the fetus, and the maternal placenta (Decidua basalis), which develops from the maternal uterine tissue.

Cytotrophoblastic cells penetrate into the overlying syncytium until they reach the maternal endometrium, and form a thin outer cytotrophoblastic shell that serves to unite the endometrium through the chorionic sac stem or anchoring villi that are directed from the chorionic plate to the decidua basalis.