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Questions and Answers
In which plane does the primitive streak appear on the embryonic disc?
In which plane does the primitive streak appear on the embryonic disc?
What is the result of the proliferation and movement of cells of the epiblast?
What is the result of the proliferation and movement of cells of the epiblast?
What is the term for the inward movement of epiblastic cells that forms the primitive groove and pit?
What is the term for the inward movement of epiblastic cells that forms the primitive groove and pit?
What is the term for the embryonic connective tissue formed by cells leaving the deep surface of the primitive streak?
What is the term for the embryonic connective tissue formed by cells leaving the deep surface of the primitive streak?
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What is the characteristic shape of the cells that make up the mesenchyme?
What is the characteristic shape of the cells that make up the mesenchyme?
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What is the main function of mesenchyme in the embryo?
What is the main function of mesenchyme in the embryo?
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What type of cells are formed from the epiblast, excluding the cells that form the embryonic endoderm?
What type of cells are formed from the epiblast, excluding the cells that form the embryonic endoderm?
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Which signaling molecules are involved in specifying germ cell layer fates?
Which signaling molecules are involved in specifying germ cell layer fates?
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From which structure do mesenchymal cells migrate widely?
From which structure do mesenchymal cells migrate widely?
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What type of cells can mesenchymal cells differentiate into?
What type of cells can mesenchymal cells differentiate into?
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Study Notes
Gastrulation
- Formation of the primitive streak on the surface of the epiblast of the bilaminar embryonic disc is the first morphologic sign of gastrulation
- By the beginning of the third week, a thickened linear band of epiblast appears caudally in the median plane of the dorsal aspect of the embryonic disc
- The primitive streak results from the proliferation and movement of cells of the epiblast to the median plane of the embryonic disc
- As soon as the primitive streak appears, it is possible to identify the embryo’s craniocaudal axis, cranial and caudal ends, dorsal and ventral surfaces, and right and left sides
Development of the Primitive Streak
- The primitive streak elongates by addition of cells to its caudal end, while its cranial end proliferates to form the primitive node
- A narrow groove, the primitive groove, develops in the primitive streak, which is continuous with a small depression in the primitive node, the primitive pit
- The primitive groove and pit result from the invagination (inward movement) of epiblastic cells
Formation of Mesenchyme and Mesoderm
- Cells leave the deep surface of the primitive streak and form mesenchyme, an embryonic connective tissue consisting of small, spindle-shaped cells
- Mesenchyme forms the supporting tissues of the embryo, such as most of the connective tissues of the body and the connective tissue framework of glands
- Some mesenchyme forms mesoblast (undifferentiated mesoderm), which forms intraembryonic mesoderm
Formation of Embryonic Endoderm and Ectoderm
- Cells from the epiblast, as well as from the primitive node and other parts of the primitive streak, displace the hypoblast, forming embryonic endoderm in the roof of the umbilical vesicle
- The cells remaining in the epiblast form the embryonic ectoderm
Signaling Molecules and Germ Cell Layer Fates
- Signaling molecules (nodal factors) of the transforming growth factor-β superfamily induce formation of mesoderm
- Other signaling molecules (e.g., Wnt3a, Wnt5a, and FGFs) also participate in specifying germ cell layer fates
- Transforming growth factor-β (nodal), a T-box transcription factor (veg T), and the Wnt signaling pathway are involved in specification of the endoderm
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Description
This quiz covers the formation of the primitive streak on the surface of the epiblast during gastrulation, a crucial stage in embryonic development.
