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| 1.Craniocaudal folding caused by growth of CNS 2. Lateral folding caused by growth of somites, amnion, and other components of lateral body wall. 3. craniocaudal folding and lateral folding change shape of embryo from a two-dimensional disk to a 3-dimensional cylinder. |
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| process establishes three definitive germ layers of embryo, thereby forming a trilaminar embryonic disk by day 21 of development. first indication primitive streak |
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| gives rise to epidermis, the central and peripheral nervous systems, the retina of eye. |
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| source of epithelial linings of respiratory passages and GI tract, glands into GI tract, glandular cells of associated organs liver, pancreas. |
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| gives rise to smooth muscular coats, connective tissues, vessels associated with tissues and organs, forms most of cardiovascular system. blood cells bone marrow, skeleton, striated muscle |
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| first sign of gastrulation consists of: primitive groove, node, pit. composed of epiblast. |
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| cells leave the deep surface of Primitive groove and form loose network of embryonic tissue called mesenchyme or mesoblast, which forms the intraembryonic mesoderm |
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| some cells of epiblast displace hypoblast forming embryonic endoderm in roof of yolk sac. |
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| caudal to the primitive streak and future site of anus, where epiblast and hypoblast cells are fused. |
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| ectoderm, intraembryonic mesoderm, and endoderm of trilaminar embryonic disk. |
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| germ layer that orms during week 3 in contrast to extraembryonic mesoderm, which formed during week 2. |
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| connects paraxial mesoderm and lateral mesoderm. forms longitudinal dorsal ridge known as urogenital ridge, involved in future kidney and gonad formation. |
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| thin plate mesoderm in which intraembryonic coelem forms, dividing lateral mesoderm into 2 layers: a. intraembryonic somatic mesoderm b.intraembryonic visceral mesoderm |
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| induces overlying embryonic ectoderm to thicken and from neural plate. induces formation of vertebral bodies. forms nucleus pulposus of each intervertebral disk in a newborn. |
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| where primordium of the heart begins to develop |
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| Primordium of CNS. developing notochord induces overlying embryonic ectoderm to thicken and form neural plate |
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| as notochord develops embryonic ectoderm thickens to form an elongated plate of thickened epithelial cells. |
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| lie along crest of each neural fold and form neural crest which give rise to spinal ganglia and the ganglia of autonomic nervous system |
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| CN ganglia V,VII,IX,X; meningial layers, schwann cells, cells of suprarenal medulla, several skeletal and muscular components in head. |
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| arise from division of paraxial mesoderm that pair into cuboidal bodies. |
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| blood vessel formation begins in extraembryonic mesoderm of yolk sac connecting stalk and chorion. |
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| develop from endothelial cells as the vessels develop in walls of yolk sac and allantois at end of third week. |
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| Blood formation does not begin until the fifth week and occurs in embryonic mesenchyme, the liver, spleen, bone marrow, and lymph nodes. |
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| Primordial Cardiovascular System |
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| forms from mesenchymal cells in cardiogenic area, by formaing a primitive heart tube. form primordial cardiovascular system. cardiovascular system first functional system. |
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| two endocardial heart tubes arise from cardiogenic mesoderm. these fuse to form primitive heart tube, which develops into endocardium. |
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| Extraembryonic somatic mesoderm and two layers of trophoblast constitute the chorion. |
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| chorion forms the wall of chorionic sac which is area surrounding yolk-sac and the amniotic cavity. |
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| measures chorionic sac diameter. measurement is valuable for evaluating very early embryonic development and pregnancy outcome. |
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| grow from cytotrophoblast that grow into the syncytiotrophoblast. Thought to be induced by the underlying extraembryonic somatic mesoderm. develop into chorionic villi of placenta. |
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| 3rd week embyonic blood flows slowly through capillaries in chorionic wall. oxygen & nutrients of mom in intervillous space diffuse through walls of villi and enter embryo's blood. CO2 & waste diffuse from blood in fetal capillaries through wall of villi into maternal blood. |
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