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Fertilization and normal embryonic and early fetal development
Published in Hung N. Winn, Frank A. Chervenak, Roberto Romero, Clinical Maternal-Fetal Medicine Online, 2021
Asim Kurjak, Ritsuko K. Pooh, Aida Salihagic-Kadic, Iva Lausin, Lara Spalldi-Barisic
Along with the implantation process, changes occur in the embryoblast to produce a bilaminar embryonic disc, composed of the epiblast and the hypoblast. Early in the 2nd week, the amniotic cavity appears as a space lined with amnioblasts derived from the epiblast. By the end of the 2nd week, the embryonic disc becomes oval in shape. Along the median line in the posterior region of the embryonic disc, a thickening of the epiblast called the primitive streak appears, and it defines the longitudinal axis of the embryo. During the 3rd week, lateral epiblast cells migrate medially, enter the primitive streak, and then converge to form the primitive groove.
De Fabrica Humani Corporis—Fascia as the Fabric of the Body
Published in David Lesondak, Angeli Maun Akey, Fascia, Function, and Medical Applications, 2020
In embryology the question “Where does it comes from?” usually leads to the so-called germ layers.18 In human development these three germ layers appear in approximately the third week after conception.19 In common embryology germ layers are regarded as morphological organ-forming units from which the various tissues and organs develop, resulting in a functioning organism. In most textbooks the three primary germ layers are referred to as ectoderm, mesoderm, and endoderm (sometimes mentioned as ectoblast (or epiblast), mesoblast, and endoblast (or hypoblast).
The embryonic period
Published in Frank J. Dye, Human Life Before Birth, 2019
As we watched what transpires during this third week, we would observe cells in the epiblast moving toward both the primitive streak and primitive node. As the cells arrive at these two locations, they would sink beneath the surface epiblast. Some of the sinking cells would sink deeper and displace the hypoblast to give rise to embryonic endoderm; other cells would sink to an intermediate position to give rise to mesoderm.
Application of amniotic membrane in reconstructive urology; the promising biomaterial worth further investigation
Published in Expert Opinion on Biological Therapy, 2019
Jan Adamowicz, Shane Van Breda, Dominik Tyloch, Marta Pokrywczynska, Tomasz Drewa
The mammalian embryo is enclosed in the fluid filed amniotic sac of the placenta, surrounded by the AM. In humans, 6–7 days after fertilization, AM starts to develop during blastocyst implantation in the endometrium [6]. Subsequently, the embryoblast (inner cell mass within the blastocyst) differentiates into a bilaminar disc composed of the hypoblast and epiblast. Eventually, amnioblasts derived from the epiblast invade the space between the trophoblast and the embryonic disc, migrating to the inner amniotic layer and gradually constitute the external lining of the amniotic cavity. The amniotic and chorionic fetal membranes separate the embryo from the endometrium. The amniochorionic membrane forms the outer limits of the sac that encloses the embryo, while the innermost layer of the sac is the AM [7].