Gatrulation
Terms
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- Gastrulation
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-Formation of germ layer.
-A single layered blastula becomes a trilaminar structure with an outher ectodermal, middle mesodermal and innder endodermal layer.
-Through cell migration from surface of blastula to its interior - What does the ectodermal layer become?
- Epidermis of the skin and neural tissue
- What does the endodermal layer become?
- lining of gastrointestinal and respiratory tract
- What does the mesodermal layer become?
- Urogenital, circulatory and supportive muscular and skeletal systems
- Gatrulation in Primitive Chordates (Aphioxus/ Lancelet)
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-Blastoderm at vegetal pole flattens and invaginates
-Formation of a caity= primitive gut/archenteron
-Opening of primitive gut=blastopore
-Endodermal and mesodermal structures relocate from the surface of the embryo to interior, forming a trilaminar embryo=gastrula - Gastrulation in Amphibians
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-Invagination cannot occur (yolk-filled cells in veg. hemisphere)
-Cells from surface ( cross point of veg.and a. hem.) move to interior, cleft, pre primitive gut.
-cleft deepens, bc/of inflow of endodermal cells (below) and mesodermal (above=
-circular blastopore formed
-blastocoele destroyed, yolk laden cells at veg.pole move to inner and trilaminar embryo is formed - Gastrulation in mammals
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-closely resembles that of birds
-Blastocyst cavity=empty yolk-sac cavity
-Blastocyst= formation of a layer of flat cells derived from embr. disc (lower surface)
- Cells of hypoblast extends and line the blastocyst cavity, forming a bilaminar yolk sac.
- Dev. of germ layers, formation of p. streak and node. Streak acts as initiation site for gastrulation. Adjacent epiblast cells lose ability to respond->only 1 p.streak formed - Left/right symmetry
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-Organs, vertebrates, asymmetrically in thoracic and abdominal cavities
-regulated by molecule processes
-pattern dev. during gastrulation -
Twinning
-what it is
-two types -
-2 ind. develop in 1pregnancy in an animal (monotocous)
-Dizygotic: two ova, fert. by separate spermatozoa, single breeding cycle
-Monozygotic: single ovum, fert. by 1 spermatozoon. 3 diff. ways:
1. Two-blastomere stage: each b. give rise to separate ind. 30% humans.
2. Inner cell mass stage: duplication of inner cell mass. Dev. with separate amnion, but share yolk sac and chorion. 70% humans.
3. Embryonic disc stage: formation of 2p.streak, each giving rise to separate ind. Share amnion, yolk sac and chorion. 1% human