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Day 3
Published in Bertha Alvarez Manninen, Dialogues on the Ethics of Abortion, 2022
About two weeks after fertilization, the “primitive streak” begins to form, which is the precursor to the formation of the nervous system. It’s the beginning of the human animal – an individual functioning human organism.37
The embryonic period
Published in Frank J. Dye, Human Life Before Birth, 2019
If we were somehow miniaturized and we entered the amniotic cavity of a beginning third-week human conceptus, we could look down on top of the two-layered embryonic disc, the epiblast, which would have a somewhat circular outline. Early in the third week, a thickened ridge of cells would appear on the midline of the epiblast. This ridge is called the primitive streak and is a characteristic of early developing higher vertebrates (reptiles, birds, and mammals). At the (future) head end of the primitive streak is a mound of cells, the primitive node.
Conclusion
Published in Shaun D. Pattinson, Revisiting Landmark Cases in Medical Law, 2018
The 1990 Act, which has subsequently been amended,71 imposed a licensing requirement on the creation, storage and use of embryos outside the body and prohibited some specific activities in connection with human gametes and embryos. When enacted, it was envisaged that human embryos would continue to be created by fertilisation involving a sperm joining with an egg. It was then known that if an embryo splits at an early stage – before the development of the so-called primitive streak – the resulting embryos will be genetically identical. That is to say, that embryos produced by embryo splitting will be clones, which is how identical twins occur. Dolly was produced by a method not envisaged in 1990 but was a clone in the sense of being (almost) genetically identical to another sheep. She was the product of part of an egg joining with a body (somatic) cell. In her case, that somatic cell was taken from the mammary gland of a sheep, but any somatic cell would have done. The nucleus was first removed from an egg. The nucleus-free (enucleated) egg was then fused with the mammary gland cell by electric stimulation and chemical signals were used to trigger the onset of embryonic development.
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
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].