Embryology Lecture 2-Week 2 and 3 Development of Bilaminar and Trilaminar Disc Flashcards

1
Q

By ______ post-fertilization - implantation into the endometrial wall is completed.

A

By 10 days post-fertilization - implantation into the endometrial wall is completed.

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2
Q

The trophoblast differentiate into:

A

The trophoblast differentiate into:

  1. ) Cytotrophoblasts
    - Dervied from Trophoblasts
    - Mitotic mononuclear cells
    - Migrate to become Syncytiotrophoblasts
  2. ) Syncytiotrophoblasts- -Multinuclear cells without cell membranes
    - Responsible for erosion into the endometrium
    - Produce the HCG preserving corpus luteum activity (secretion of E and P4)
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3
Q

Describe the establishment of embryonic and bilaminar structure:

A

After fertilization occurs:

  • A small space is created within the embryoblast
  • Amnioblasts surround this space enclosing the cavity
  • This space will go on to become the amniotic cavity
  • The embryoblast forms a flat bilayer structure, embryonic disc, consisting of two layers:

  1. ) Epiblast-Columnar cells
  2. ) Hypoblast-Small cuboidal cells
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4
Q

Describe the establishment of maternal blood communication:

A
  • By Embryonic Day 11-12 the blastocyst will completely embed in the endometrium and the surface defect will close and heal
  • Synctiotrophoblasts will penetrate deeper into the maternal capillaries termed sinusoids.
  • This establishes uteroplacental circulation
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5
Q

Describe some support structures to the embedded blastocyst:

A
  • Exocoelomic membrane- Lines inner surface of cytotrophoblasts
  • Along with hypoblasts this forms the lining of the primitive yolk sac (also termed the exocoelomic cavity)
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6
Q

What is the function of the yolk sac?

A

to provide nourishment for the developing embryo

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7
Q

Describe the formation of the Extraembryonic Mesoderm:

A
  • Cells intervene between the cytotrophoblast layer and the yolk cavity forming the extraembryonic mesoderm.
  • This layer fills all space between the trophoblasts and the amnion and exocoelomic cavity.
  • Within this mesoderm a space termed the extraembryonic cavity or chorionic cavity is formed surrounding the yolk sac and amniotic cavity.
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8
Q

It is within the _______ cavity that villi will develop to allow for uteroplacental circulation.

A

It is within the chorionic cavity that villi will develop to allow for uteroplacental circulation.

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9
Q

The extraembryonic mesoderm layer further differentiates into:

A

The extraembryonic mesoderm layer further differentiates into:

  • Somatic layer- lines and supports/surrounds the cytotrophoblast and amnion
  • Sphlanchnic layer - lines and supports/surrounds the yolk sac
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10
Q

_________ form the primary villi establishing communication with the chorionic cavity.

A

Trophoblasts form the primary villi establishing communication with the chorionic cavity

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11
Q

The hyoblast layer produces cells that migrate along the exocoelomic membrane and form a new cavity termed the _________. These migrating cells pinch off the yolk sac from the __________.

A

The hyoblast layer produces cells that migrate along the exocoelomic membrane and form a new cavity termed the secondary or definitive yolk sac. These migrating cells pinch off the yolk sac from the endometrium.

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12
Q
A
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13
Q

At the end of week 2:

  • Chorionic cavity continues to expand.
  • The somatic layer of mesoderm is now properly termed _______ _______.
  • The connecting stock is now visible traversing the extraembryonic mesoderm.
  • This connecting stock will go on to become the _______ _____.
A

At the end of week 2:

  • Chorionic cavity continues to expand.
  • The somatic layer of mesoderm is now properly termed chorionic plate.
  • The connecting stock is now visible traversing the extraembryonic mesoderm.
  • This connecting stock will go on to become the umbilical cord.
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14
Q

Early week 3 development is characterized by 6 things:

A
  • Appearance of Primitive Streak
  • Development of the Notochord
  • Transition from two layer embryo to three layer embryo (gastrula)
  • Establishment of body axes
  • Further growth of the embryo
  • Further development of uteroplacental circulation
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15
Q

Describe the formation of the primitive streak:

A
  • Forms in the surface of the upper layer, the epiblast during week 3
  • Establishes the body axis
  • Becomes the site of gastrulation.
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16
Q

Describe the formation of the primitive groove and pit.

A
  • The primitive streak deepens and can be properly termed the primitive groove as the sides bulge around it.
  • At the cephalic end of the streak, an elevated area termed the primitive node forms and surrounds a small cavity termed the primitive pit.
17
Q

Describe gastrulation:

A
  • Cells of the epiblast layer migrate towards the primitive streak.
  • They detach from the upper layer and move beneath it in a movement termed invagination.
  • These cells have different fates
  • Endoderm or endodermal layer
  • Mesoderm or the mesoderm layer
  • Ectoderm or ectodermal layer
18
Q
  • Cell migration continues _______ and _______ beyond the confines of the embryonic disc
  • Cranially the cells pass on the sides of the prechordal plate between the tip of what will be the notochord and the oropharyngeal membrane
  • Cranially migrating cells can be properly termed ________ _____.
A

Cell migration continues laterally and cranially beyond the confines of the embryonic disc.

  • Cranially the cells pass on the sides of the prechordal plate between the tip of what will be the notochord and the oropharyngeal membrane
  • Cranially migrating cells can be properly termed prenotochordal cells
19
Q

Describe the formation of the Notochord:

A
  • A mix of prenotochord cells and cells of the hypoblast develop the notochordal process.
  • Cells from the endoderm replace the cells resident within the notochord process creating a solid cord of cells termed the definitive notochord.
  • The notochord underlies the neural tube and will eventually induce development of the axial skeleton.
20
Q
A
21
Q

Describe Cephalo-Caudal Development:

A
  • The cephalocaudal axis is now established
  • The primitive streak will migrate caudally through development.
  • Cells of the notochord and prenotochord regions extend cranially to the area of the prechordal plate and caudally to the primitive pit.
  • Cloacal membrane forms at the caudal end of the embryonic disc.
  • The posterior wall of the yolk sac forms a small diverticulum in the connecting stock termed the allantois, a rudimentary structure in humans.
  • Both the oropharyngeal and cloacal membrane represent areas of tightly adherent ectoderm and endoderm. ** no mesoderm
22
Q

After the notochord forms, the cephalocaudal axis is established, and the cloacal membrane has formed, what does the mesoderm differentiate into?

A
  • Paraxial mesoderm near cranial end
  • Intermediate mesoderm near midstreak region
  • Lateral mesoderm plate closer to the caudal part of the streak
23
Q

The primitive streak begins to disappear during which week of development?

A

The fourth week

24
Q

Describe how the circulatory connection between the placenta and the embryo is made (Uteroplacental circulation).

A
  • The trophoblast layer is also transitioning as mesodermal cells penetrate the villi and grow into what is termed the secondary villus.
  • By the end of the third week of development the mesodermal cells in the villus begin differentiation into blood cells and blood vessels forming the villous capillary system.
  • The villus is now termed the definitive placental villus.
  • Capillaries in the villus make contact with the capillaries in the mesoderm of the chorionic plate and in the connecting stalk
  • These vessels now establish contact with the intraembryonic circulatory system and a connection is now made between the placenta and embryo.
  • The cytotrophoblast cells are also continuing to penetrate the maternal endometrium.
  • Communication is established between villous stems termed the outer cytotrophoblast shell.
  • This shell will surround the trophoblast layer completely and affix the chorionic sac to the maternal endometrium.
  • The chorionic cavity continues to enlarge and attaches to the trophoblastic cell by the connecting stock (umbilical cord), the connection between the placenta and embryo.
25
Q
A
26
Q
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27
Q

What are cytotrophoblasts?

A
  • Dervied from Trophoblasts
  • Mitotic mononuclear cells
  • Migrate to become Syncytiotrophoblasts
28
Q

What are Syncitiotrophoblasts?-

A
  • Multinuclear cells without cell membranes
  • Responsible for erosion into the endometrium
  • Produce the HCG preserving corpus luteum activity (secretion of E and P4)