What happens at day 8
- embryo partial embedded into endometrium
- small cavity appears between embryoblast called amniotic cavity
Describe state of surrounding endometrium at day 8
- highly vascular
- tissue is edematous
- large glands secrete abundant glycogen and mucus
Describe state of embryoblast at day 8
-diff’s into 2 layers
1 hypoblast - layer of small cuboidal cells adjacent to blastocyst cavity
2 epiblast - columnar cells adjacent to aminotic cavity. Cells cytotrophoblast are called amnioblasts
Describe state of trophoblast at day 8
How is the outer layer formed
- diff’s into 2 layers
1 synctioblast- outer multi nucleated cell layer without visible cell boundaries
2 cytotrophoblast - inner mononucleated cell layer with visible cells boundary
-cytotrophoblast cells divide migrate to synctioblast where they fuse and lose their cell boundaries
Describe state of embryo at day 9, state of penetration defect , of trophoblast
State of blastocyst cavity describe
- blastocyst deeply ( not completely) embedded in endometrium
- penetration defect closed by fibrin Coagulum
- trophoblast develops vacuoles in synctium at embryonic pole wc fuse to form lacunae
-blastocyst cavity now called exocoelomic ( primitive yolk sac ) cavity surrounded by exocoelomic membrane ( Heuser ) made of hypoblast and flat cells from hypoblast
Describe state of embryo at day 11-12
State of trophoblast
- blastocyst completely embedded in endometrium with slight protrusion into lumen
- endometrium epi covers implantation defect
-embryonic pole has lacunae in synctium that form inter communication network whilst abembryonic has cytotrophoblast cells
How does lacunae become continuous with maternal vessels and when and the outcome
State of maternal capillaries and name
- at day 11-12
- synctium cells evade and erode endothelial lining of maternal capillaries wc become continuous with lacunae
- maternal blood enters lacunae gains flow through trophoblast system and establishes uteroplacental circulation
-dilated and congested and called sinusoids
What happens at disc during day 11-12
-yolk sac cells appear between outer epiblast and inner cytotrophoblast and form fine loose CT called extraembryonic mesoderm
What develops In extra embryonic mesoderm during day 11-12 and what does it surround
-cavities which fuse To form chorionic Cavity or extra embryonic cavity
/primitive yolk sac and aminotic cavity except where disc is attached to trophoblast
Name of cytotrophoblast and yolk sac coverings
- extra embryonic somatic mesoderm
- extra embryonic splanchnic mesoderm
State of endometrium at day 11-12 and name of reactions that occur
Where is the reaction 1st confined to and outcome
- cells polyhedral filled with lipids and glycogen
- intercellular space filled with extravasate and tissue edematous
- reactions called decidua reactions
- cells immediately around implantation site but soon spreads to entire endometrium
State of embryo at day 13
State of trophoblast and hypoblast in detail the changes that occur
- surface defect has healed
- has villus structure formed by cells of epiblast that proliferate , form columns and are surrounded by synctium
- produces cells that migrate inside exocoelomic membrane proliferate and form new cavity called definitive or secondary yolk sac
How is exocoelomic cyst formed
-during formation of definitive yolk sac exocoelomic cavity pinched off into fragments which join to form cyst
What Occurs to extra embryonic coelom at day 13
Name of mesoderm lining now
/it expands and forms large chorionic cavity and mesoderm lining now called chorionic plate
What later on happens to connecting stalk
-becomes umbilical cord with development of blood vessels
