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Embryology (macro) > 2nd week of development > Flashcards

2nd week of development Flashcards

1
Q

3 events take place during the 2nd week of development

A

I. Completion of implantation of the blastocyst

II. Formation of bilaminar embryonic disc(epiblast and hypoblast)

II. Formation of extraembryonic structures(amniotic cavity, amnion, umbilical vesicle [yolk sac], connecting stalk, and chorionic sac)

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2
Q

DAY 8

At the eighth day of development, the blastocyst is partially embedded in the ___

A

endometrial stroma

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3
Q

DAY 8

At the eighth day of development, the ___ is partially embedded in the endometrial stroma

A

blastocyst

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4
Q

DAY 8

In the area over the embryoblast, the trophoblast has differentiated into two layers.

What are they?

A

(1) an inner layer of mononucleated cells, the cytotrophoblast
(2) an outer multinucleated zone without distinct cell boundaries, the syncytiotrophoblast

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5
Q

DAY 8

Mitotic figures are found in the ___

A

cytotrophoblast

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6
Q

DAY 8

cells in the cytotrophoblast divide and migrate into the ___, where they fuse and lose their individual cell membranes.

A

cytotrophoblast

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7
Q

DAY 8

Cells of the inner cell mass or embryoblast also differentiate into two layers

→ What are these 2 layers

A

(1) hypoblast layer - a layer of small cuboidal cells adjacent to the blastocyst cavity
(2) the epiblast layer - a layer of high columnar cells adjacent to the amniotic cavity,

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8
Q

DAY 8

The hypoblast and epiblast layers together form a flat ovoid shaped disc called the __

A

bilaminar embryonic disc

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9
Q

DAY 8

Cells of the inner cell mass or embryoblast also differentiate into two layers which are hypoblast and epiblast layers → the layers form a flat disc

→ a small cavity appears within the ___

A

epiblast

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10
Q

DAY 8

a small cavity appears within the epi- blast. This cavity enlarges to become the __

A

amniotic cavity.

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11
Q

DAY 8

What are amnioblasts?

A

Epiblast cells adjacent to the cytotrophoblast

→ ogether with the rest of the epiblast, line the amniotic cavity

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12
Q

DAY 9

The blastocyst is more deeply embedded in the endometrium, and the ___ in the surface epithelium is closed by a fibrin coagulum

A

penetration defect

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13
Q

DAY 9

The blastocyst is more deeply embedded in the endometrium

→ the penetration defect in the surface epithelium is closed by a ___

A

fibrin coagulum

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14
Q

DAY 9

Describe the lacunar stage

A

The phase of trophoblast development

→ Vacuoles appear at the region of the trophoblast and they fuse to form lager lacunae

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15
Q

What is exocoelomic (Heuser’s) membrane? What does it form?

A

A thin membrane formed by the cells of the hypoblast adjacent to the cytotrophoblast

→ lines the inner surface of the cytotrophoblast

→ forms the lining of the exocoelomic cavity, or primitive yolk sac or primary umbilical vesicle

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16
Q

When is the blastocyst completely embedded in the endometrium?

A

11th - 12th day of development

17
Q

11th - 12th day of development
What happen before primordial uteroplacental circulation?

A

cells of the syncytiotrophoblast penetrate deeper into the stroma(tissue)

→ erode the maternal sinusoids (the endothelial lining of the maternal capillaries.)

→ The syncytial lacunae become continuous with the sinusoids

→ maternal blood enters the lacunar system

→ maternal blood begins to flow through the trophoblastic system

→ primordial uteroplacental circulation begins

18
Q

11th - 12th day of development
What is extraembryonic mesoderm? Its role?

A

cells which are derived from yolk sac cells form a fine, loose connective tissue

→ fills all of the space between the trophoblast externally and the amnion and exocoelomic membrane internally

19
Q

11th - 12th day of development
What is chorionic cavity?

A

Cavity developed in the extraembryonic mesoderm

20
Q

11th - 12th day of development
What is extraembryonic somatic mesoderm?

A

The extraembryonic mesoderm lining the cytotrophoblast and amnion

21
Q

11th - 12th day of development
What is extraembryonic splanchnic mesoderm?

A

the lining covering the yolk sac

22
Q

11th - 12th day of development
What is decidual reaction?

A

the endometrial connective tissue cells undergo a transformation

→ the decidual cells of the endometrium swell because of the accumulation of glycogen and lipid in their cytoplasm

23
Q

11th - 12th day of development
The primary function of the decidual reaction is __

A

to provide nutrition for the early embryo and an immunologically privileged site for the conceptus

24
Q

What happen to surface epithelium and blood flow in day 13th?

A

The surface defect in the endometrium has been completely covered by the surface epithelium

Occasionally bleeding occurs at the implantation site as a result of increased blood flow into the lacunar spaces

25
Q

DAY 13

The trophoblast is characterized by __

A

The surface defect in the endometrium has been completely covered by the surface epithelium

Occasionally bleeding occurs at the implantation site as a result of increased blood flow into the lacunar spaces

26
Q

DAY 13

The role of Cells of the cytotrophoblast

A

They proliferate locally and penetrate into the syncytiotrophoblast, forming cellular columns surrounded by syncytium.

27
Q

DAY 13

Cellular columns with the syncytial covering are known as ___

A

They proliferate locally and penetrate into the syncytiotrophoblast, forming cellular columns surrounded by syncytium.

28
Q

DAY 13

How is secondary yolk sac formed?

A

the hypoblast produces additional cells that migrate along the inside of the exocoelomic membrane

→ cells proliferate and gradually form a new cavity within the exocoelomic cavity → known as the secondary yolk sac or definitive yolk sac

29
Q

DAY 13

This secondary yolk sac is much ___ than the original exocoelomic cavity, or primitive yolk sac.

A

smaller

30
Q

DAY 13

Meanwhile, the extraembryonic coelom expands and forms a large cavity, the __

A

chorionic cavity

31
Q

DAY 13

The extraembryonic mesoderm lining the inside of the cytotrophoblast is then known as the ___

A

chorionic cavity

32
Q

DAY 13

The ___ lining the inside of the cytotrophoblast is then known as the chorionic plate.

A

extraembryonic mesoderm

33
Q

DAY 13

The only place where extraembryonic mesoderm traverses the chorionic cavity is in the ___ With development of blood vessels, the stalk becomes the___

A

connecting stalk

umbilical cord.

34
Q
  1. The second week of development is known as the week of 2’s. Formation of what structures supports this statement?
A
  1. The trophoblast differentiates into two layers: the cytotrophoblast and syncytiotrophoblast.
  2. The embryoblast forms two layers: the epiblast and hypoblast.
  3. The extraembryonic mesoderm splits into two layers: the somatic and splanchnic layers.
  4. Two cavities form: the amniotic and yolk sac cavities.

Embryology (macro) (5 decks)

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