Prenatal Development of the Facial Skeleton
D. Dixon Andrew, A.N. Hoyte David, Ronning Olli in Fundamentals of Craniofacial Growth, 2017
These two primary germ layers are soon joined by a third, the mesoderm, that comes from either side of the primitive streak at the caudal edge of the now roughly circular embryonic disc and lies between the other two layers. At about 2 weeks the primitive streak is recognized as a linear heaping-up of ectodermal cells that continue to divide at a rate comparable to other regions of the ectoderm. The production of mesodermal cells by this region is not so much the direct result of a proliferative process, but rather a rearrangement or migration of certain ectodermal cells that will assume other developmental responsibilities. This event has its parallel in the rapid change in shape and complex rearrangement of cells that characterize gastrulation in other vertebrates. The resulting trilaminar stage of development is complete by the end of the 3rd week after fertilization.
Assisted reproduction and embryo research
Marc Stauch, Kay Wheat in Text, Cases and Materials on Medical Law and Ethics, 2018
As the Warnock Report had noted, the formation of the primitive streak marks that stage in embryonic development when a new individual entity is first discernible: As for research on embryos within the first 14 days, this could be carried out (with the consent of the gamete providers) subject to the researcher having a research licence from the HFE Authority. In granting a licence the Authority needed to be satisfied that the research was ‘necessary or desirable’ for one of the purposes specified in Sch 2, para 3 of the 1990 Act. Originally these included promoting infertility treatment, increasing knowledge about congenital diseases, and improving techniques of contraception.
The beginning of life
Fredrik Svenaeus in Phenomenological Bioethics, 2017
At around one week the embryo ‘hatches’, and the trophectoderm cells – which will form the placenta – attach to the endometrial cells of the uterus. The embryo then becomes embedded in the endometrium through the process known as implantation. Rapid growth now occurs, and after about one more week the cells of the embryo begin to differentiate into the cell types that will form the tissues and organs of the foetus, a stage known as gastrulation. This is the last stage of the pre-embryo phase, after which the ‘primitive streak’ will appear, which is the structure that will develop into the spine of the embryo.
Congenital Spinal Lipomatous Malformations. Part 1. Spinal Lipomas, Lipomyeloceles, and Lipomyelomeningoceles
Published in Fetal and Pediatric Pathology, 2020
Very early, the embryonic primitive streak forms the mesoderm and produces notochordal cells in Hensen’s node that probably induce the overlying ectoderm to thicken into the neural plate [17, 31]. The neural plate, covering much of the posterior early embryo, folds medially at its lateral borders with the embryonic ectoderm, possibly by compression from the ectoderm assisted by force generated by the mesoderm [41]. When the lips of the neural folds form at the ectoderm-neural plate borders and move medially to close dorsally and mesially, the primary neural tube is formed. The posterior neuropore at the caudal end of the primary neural tube closes at the level of the future S3–S5 vertebrae (Figure 2). The primary neural tube detaches (disjunction) from the ectoderm to complete primary neurulation. Failure of disjunction or a failure of posterior neuropore closure may cause open neural tube defects, the most common malformations of spinal dysraphism. The most common open neural tube defects over the spine include myelomeningoceles and craniorachischisis totalis [17, 40, 42–44].
Anticipatory Governance and Foresight in Regulating for Uncertainty
Published in The American Journal of Bioethics, 2022
The response of the Embryo Research Licensing Committee (ERLC) in Australia may be interpreted as precautionary. In determining that the iBlastoids created at Monash University met the definition of human embryos in the Australian legislation, embryoid research will become regulated under the licensing scheme of the national regulator.2 This determination will surely impose significant costs onto researchers who will need to divert limited resources and public funding to apply for licensure and maintain onerous reporting requirements. There is a good chance that socially important and potentially beneficial research will be delayed or not done at all. The onus would be on researchers to disprove the hypothesis that embryoids can develop into an organism and presumably incur moral, if not physical, harms to the structure should the primitive streak develop at or around 14 days.
Advances in understanding vertebrate nephrogenesis
Published in Tissue Barriers, 2020
Joseph M. Chambers, Rebecca A. Wingert
Vertebrate development entails the formation of three germ layers, the ectoderm, mesoderm, and endoderm, which provide cellular blueprints for embryonic organogenesis. Ectoderm gives rise to the central nervous system and skin cells, and endoderm derivatives encompass cells that line the respiratory and digestive tracts. The mesoderm, or middle layer, produces cells that are most abundant in the human body constituting skeletal muscle, cartilage, heart, gonads, and blood, among other tissue types.1 This review will focus on a member of the mesoderm lineage: the kidney. Much of our understanding about kidney development stems from rodent models, but also has benefited from studies in other vertebrates such as fish, frogs, and birds.2The inception of mesoderm development begins with the differentiation of pluripotent epiblast cells into a transient ‘primitive streak’ zone.1Position along the anterior-posterior embryonic axis and other instructive signals regulate the regionalization of paraxial, intermediate, and lateral plate mesoderm.3
Related Knowledge Centers
- Embryonic Development
- Gastrulation
- Germ Layer
- Mesoderm
- Tissue
- Embryo
- Mesenchymal Stem Cell
- Animal Embryonic Development
- Bilaminar Embryonic Disc
- Symmetry In Biology