Applications of Placenta-Derived Cells in Veterinary Medicine
Ornella Parolini, Antonietta Silini in Placenta, 2016
In most of the mammals, the tubaric period ends at the morula stage. Compaction of the morula, preliminary to blastulation, occurs mainly in the uterus. The process leads to the formation of a unilaminar disc named the blastocyst that displays a central fluid-filled cavity, the blastocyst cavity, and an inner cell mass (ICM) that differentiates peripherally. The blastocyst expands under the osmotic pressure inside until the rupture of the surrounding ZP via hatching. In humans and primates, the embryo implants into the uterine mucosa, whereas in domestic animals placentation occurs at a much more advanced stage. The ICM then becomes bilaminar (bilaminar embryonic disc) around the time of blastocyst, hatching by differentiating a flattened cell population facing the blastocyst cavity, referred as hypoblast, and an external multilayered group of cells, named the epiblast (Figure 12.2). The hypoblast gradually forms a complete inner lining beneath the epiblast and the trophectoderm delimitating the primitive yolk sac. The hypoblast forms the inner epithelium of the yolk sac, and depending on the species, may become engaged in placentation. Differently from humans, the bilaminar embryos of domestic animals lose the trophectoderm that covers the epiblast, which consequently remains exposed to the uterine environment (Figure 12.2). The hatching blastocyst, which retains the spherical shape in humans, becomes gradually elongated in domestic animals (Figure 12.2). The formation of the amnion in humans occurs earlier (at the end of blastulation) than in domestic mammal embryos (at an early stage of gastrulation), and through different modalities. Indeed, the formation occurs in primates through cavitation, whereas in domestic animals it follows a more complex folding process.
De Fabrica Humani Corporis—Fascia as the Fabric of the Body
David Lesondak, Angeli Maun Akey in 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
Frank J. Dye in Human Life Before Birth, 2019
The roof of the yolk sac consists of the lower layer (hypoblast) of the embryonic disc; the rest of it is derived from trophoblast (see Figures 8.5 and 8.6). Although human yolk sacs do not contain yolk and have only a temporary existence, they are the source of two important kinds of cells: (1) primordial germ cells, which give rise to the gametes of adult life, and (2) the first blood cells formed by the conceptus.
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].
Related Knowledge Centers
- Blastodisc
- Chorion
- Epiblast
- Inner Cell Mass
- Primitive Streak
- Yolk Sac
- Embryology
- Cellular Differentiation
- Blastocyst
- Symmetry In Biology