Questions and Answers
During gastrulation, what replaces the hypoblast cells?
What is the name of the cavity formed by the fluid accumulation in the extraembryonic mesoderm layer?
What is the name of the layer of cells that forms between the exocoelomic membrane and cytotrophoblast?
What is the term for the process by which mesodermal cells form clusters that eventually form blood vessels?
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What is the name of the remnant that forms after the pole of the primary yolk sac pinches off and separates from the original yolk sac?
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What is the term for the process by which vessels sprout from other vessels?
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What is the name of the membrane that lines the primary yolk sac?
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What is the name of the process by which the endoderm lining the definitive yolk sac becomes the lining of the embryonic gut tube?
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What is the name of the stage during which the blastocoel is lined by cytotrophoblast?
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What is the name of the layer of cells that forms the lining of the embryonic gut tube?
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Study Notes
Somite Development
- Paraxial mesoderm differentiates into clusters of cells (somites) on both sides of the embryo
- Somites differentiate into occipital, cervical, thoracic, lumbar, sacral, and coccygeal somites
Somite Derivatives
- Sclerotome: cells migrate medially around the notochord to form the vertebral column and base of the skull
- Myotome: cells divide into two groups (epaxial and hypaxial) and form most skeletal muscles of the body
- Dermatome: cells migrate under the ectoderm (epidermis) to form the dermis and subcutaneous tissue
Body Cavities
- The intra-embryonic coelom is the primordium of the body cavity
- The body cavity will give rise to the pericardial cavity, pericardioperitoneal canals, and peritoneal cavity during week 4
- Each body cavity (pericardium, pleural, and peritoneal) is composed of both visceral and parietal serous membranes
- Visceral serous membrane is adhered to the surface of the organ and is derived from splanchnic mesoderm
- Parietal serous membrane lines the cavities and is derived from somatic mesoderm
Embryonic Development
- Week 2: uterine lining closes behind the implanting embryo
- Week 2: blastocyst has penetrated the endometrium about halfway, and continued growth of syncytiotrophoblast
- Week 2: formation of amnionic cavity, a fluid-filled space within the embryoblast
Formation of Bilaminar Disk
- Epiblast gives rise to the embryo proper and amnion
- Hypoblast gives rise to the yolk sac and allantois
- Exocoelomic membrane forms from hypoblast cells
Formation of Yolk Sac
- Hypoblast cells proliferate and migrate to cover the inner surface of cytotrophoblast (exocoelomic membrane)
- Primary yolk sac (lined by exocoelomic membrane) forms, and fluid accumulates to open up spaces within the extraembryonic mesoderm layer
- Spaces eventually fuse to form the extraembryonic coelom (or chorionic cavity) between two layers of extraembryonic mesoderm
- Pole of primary yolk sac farthest from the bilaminar germ disk pinches off and separates from the original yolk sac to form a remnant of the primary yolk sac and leaving the remainder to be called the secondary yolk sac
- Gastrulation results in the replacement of hypoblast by endoderm
- Definitive yolk sac (lined by endoderm) forms
Blood and Blood Vessels
- Vasculogenesis: mesodermal cells form clusters (blood islands) and blood islands form vessels
- Angiogenesis: vessels sprout from other vessels
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Description
Test your knowledge on the development of somites, including paraxial mesoderm, sclerotome, myotome, and dermatome. Learn about the formation of the vertebral column, skeletal muscles, and more.
