Table 1.
Glossary
TermDefinition
Endometrium Innermost lining of the uterus; provides the surface for blastocyst implantation 
Blastocyst Pre-implantation embryo; consists of three cell types: trophoblast, primitive endoderm, and inner cell mass 
Inner cell mass Unpolarized pluripotent stem cells that are considered to be in the naive pluripotent state 
Epiblast Pluripotent stem cells that transition from naive to primed state as cells of the ICM undergo apico-basal polarization 
Trophectoderm/trophoblast Extraembryonic cells that give rise to the chorion 
Extraembryonic primitive endoderm Extraembryonic cells that give rise to the yolk sac 
Amniotic ectoderm Derived from epiblast cells underlying the invading trophectoderm during implantation 
Amniotic sac An asymmetric cyst formed by lumenal polarization of epiblast cells, with squamous amnion cells on one side and pluripotent epiblast cells on the other side 
Amniotic cavity Lumenal cavity enclosed by the amniotic sac 
Pro-amniotic/epiblast cavity Lumenal cavity surrounded by recently polarized epiblast cells, before amnion fate determination 
Gastrulation Developmental process by which all three embryonic germ layers are established 
Primitive streak Streak-shaped domain that forms in the posterior of the embryonic disc, marking the beginning of gastrulation 
Carnegie collection Collection of human embryos held at the Carnegie Institution of Washington 
Warnock 14-d rule Rule that limits the research on human embryos to the first 14 d of development, based on the 1984 Report of the Committee of Inquiry into Human Fertilization and Embryology, chaired by Mary Warnock 
Turing patterning Reaction-diffusion–based activator/inhibitor model of patterning, first proposed by Alan Turing in 1952 
TermDefinition
Endometrium Innermost lining of the uterus; provides the surface for blastocyst implantation 
Blastocyst Pre-implantation embryo; consists of three cell types: trophoblast, primitive endoderm, and inner cell mass 
Inner cell mass Unpolarized pluripotent stem cells that are considered to be in the naive pluripotent state 
Epiblast Pluripotent stem cells that transition from naive to primed state as cells of the ICM undergo apico-basal polarization 
Trophectoderm/trophoblast Extraembryonic cells that give rise to the chorion 
Extraembryonic primitive endoderm Extraembryonic cells that give rise to the yolk sac 
Amniotic ectoderm Derived from epiblast cells underlying the invading trophectoderm during implantation 
Amniotic sac An asymmetric cyst formed by lumenal polarization of epiblast cells, with squamous amnion cells on one side and pluripotent epiblast cells on the other side 
Amniotic cavity Lumenal cavity enclosed by the amniotic sac 
Pro-amniotic/epiblast cavity Lumenal cavity surrounded by recently polarized epiblast cells, before amnion fate determination 
Gastrulation Developmental process by which all three embryonic germ layers are established 
Primitive streak Streak-shaped domain that forms in the posterior of the embryonic disc, marking the beginning of gastrulation 
Carnegie collection Collection of human embryos held at the Carnegie Institution of Washington 
Warnock 14-d rule Rule that limits the research on human embryos to the first 14 d of development, based on the 1984 Report of the Committee of Inquiry into Human Fertilization and Embryology, chaired by Mary Warnock 
Turing patterning Reaction-diffusion–based activator/inhibitor model of patterning, first proposed by Alan Turing in 1952 

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