Embryology Week 2 Flashcards

1
Q

What happens at day 8

A
  • embryo partial embedded into endometrium

- small cavity appears between embryoblast called amniotic cavity

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2
Q

Describe state of surrounding endometrium at day 8

A
  • highly vascular
  • tissue is edematous
  • large glands secrete abundant glycogen and mucus
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3
Q

Describe state of embryoblast at day 8

A

-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

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4
Q

Describe state of trophoblast at day 8

How is the outer layer formed

A
  • 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

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5
Q

Describe state of embryo at day 9, state of penetration defect , of trophoblast

State of blastocyst cavity describe

A
  • 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

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6
Q

Describe state of embryo at day 11-12

State of trophoblast

A
  • 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

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7
Q

How does lacunae become continuous with maternal vessels and when and the outcome

State of maternal capillaries and name

A
  • 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

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8
Q

What happens at disc during day 11-12

A

-yolk sac cells appear between outer epiblast and inner cytotrophoblast and form fine loose CT called extraembryonic mesoderm

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9
Q

What develops In extra embryonic mesoderm during day 11-12 and what does it surround

A

-cavities which fuse To form chorionic Cavity or extra embryonic cavity

/primitive yolk sac and aminotic cavity except where disc is attached to trophoblast

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10
Q

Name of cytotrophoblast and yolk sac coverings

A
  • extra embryonic somatic mesoderm

- extra embryonic splanchnic mesoderm

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11
Q

State of endometrium at day 11-12 and name of reactions that occur

Where is the reaction 1st confined to and outcome

A
  • 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
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12
Q

State of embryo at day 13

State of trophoblast and hypoblast in detail the changes that occur

A
  • 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
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13
Q

How is exocoelomic cyst formed

A

-during formation of definitive yolk sac exocoelomic cavity pinched off into fragments which join to form cyst

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14
Q

What Occurs to extra embryonic coelom at day 13

Name of mesoderm lining now

A

/it expands and forms large chorionic cavity and mesoderm lining now called chorionic plate

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15
Q

What later on happens to connecting stalk

A

-becomes umbilical cord with development of blood vessels

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