Second Week of Development Flashcards

1
Q

What are extra-embryonic structures

A
  • Structures not part of the embryo but essential for growth
  • Amniotic cavity
  • Amnion. (coming from the epiblast)
  • Yolk Sac or umbilical vesicle (coming from the blastocystic cavity)
  • Chorionic sac and connecting stalk
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2
Q

What happens in the second week of development

A
  • Implantation of blastocyst into the uterine wall
  • Bilamar embryonic disc forms
  • 2 trophoblastic layers contiune developing
  • Extra-embryonic structures form
  • Blastocystic cavity becomes exocoelomic cavity (primitive yolk sac)
  • End is marked by the appearance of the primary villi
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3
Q

How is the bi-laminar disc formed?

A
  • A small space is created in the between the cytotrophoblast and the inner cell mass called the amniotic cavity
  • A bilaminar plate of cells consisting of the:
    -epiblast (high columnar cells related to the amniotic cavity) and the
    -hypoblast (small cuboidal cells related to the exocoelomic cavity) which differentiates to mesodermal cells
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4
Q

Explain the development of the chorionic sac

A
  • The primary chorionic villi from the cytotrophoblast protrude into the syncytiotrophoblast.
  • The extraembryonic mesoderm forms between the cytotrophoblast, yolk sac and the amniotic cavity
  • The extraembryonic mesoderm is split into two layers by a coelom:
  • Extraembryonic somatic mesoderm lining the trophoblast and amnion
  • Extraembryonic splanchnic mesoderm, surrounding the yolk sac
  • The extraembryonic somatic mesoderm and whole trophoblast form the chorion which is the wall of the chorionic sac
  • The embryo, amniotic cavity and yolk sac are suspending by the connecting stalk (extraembryonic mesoderm)
  • The coelom = chorionic cavity
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5
Q

What development of the hypoblast happens in the second week of development?

A

The hypoblast thickens to form the prechordal plate which indicates the future site of the mouth and the future cranial region of the embryo

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6
Q

What is done to prevent the shedding of the endometrium?

A
  • Human Chorionic Gonadotropin (HCG) is released by the blastocyst causing the corpus luteum to produce estradiol and progesterone
  • In week 20 the placenta takes the hormone production control from the corpus luteum
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7
Q

How can the age and development of the embryo be evaluated?

A

By measuring the chorionic sac diameter with a transvaginal ultrasonography

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8
Q

How and when can we detect the implantation of the blastocyst to the uterine wall?

A
  • With ultrasonography
  • With highly sensitive radio-immuno-assays of HCG
  • The end of the second week
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9
Q

What is the condition where implantation occurs in the lower segment of the uterus?

A

Placenta Previa

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10
Q

What is an ectopic pregnancy?

A
  • This is when the blastocyst implants somewhere other than the uterus
  • The most common ectopic site is the uterine tube
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11
Q

What are extra things occurs in the second week?

A
  • Adjacent lacunae fuse to form lacunar networks
  • Maternal blood seeps in and out of lacunar networks when the syncytiotrophoblast destroys endometrial blood vessels
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