Day 13, Lecture 2: Human Development 2: Week 2 in human Development Flashcards Preview

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Flashcards in Day 13, Lecture 2: Human Development 2: Week 2 in human Development Deck (14)
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1
Q
A
2
Q

Events during second week of development

A
  • Implantation is completed
    • Conceptus comes to lie totally within endometrium
  • Formation of primitive uteroplacental circulation
  • Formation of bilaminar embryo
  • Formation of Extraembryonic membranes and cavities
3
Q

Formation of Primitive uteroplacental Circulation

A
  • Second week of development
  • Provides means for developing embryo to receive nutrients and get rid of waste products
    • Spaces appear in the syncytiotrophoblast to form the lacunar network
    • Endometrial stroma undergoes the decidua reaction
      • Stroma becomes hydrated and cells fill with glycogen and lipids
  • Maternal blood leaves maternal vascular system and is surrounded by conceptus tissue
  • Forms primitive placenta
  • No immunological rejection of conceptus
    • Conceptus has different genotype than mother
    • Allogenic rejection of conceptus is prevented
    • Conceptus “hides” from immune system
      • Reduction in expression of major histocompatibility complex (MHC) class I antigen
    • Conceptus produces locally immunosuppressor molecules
4
Q

Formation of Bilaminar embryonic Disk

A
  • Forms early in second week
  • Reorganization of inner cell mass
    • Epiblast
      • Embryo will form forom epiblast cells
    • Hypoblast
      • anterior visceral endoderm
        • Thickening of hypoblast at one end the bilamilar disk and this defines the cranial end of disk
5
Q

What defines the cranial end of the bilaminar embryonic disk

A
  • Anterior visceral Endoderm
    • Thickening of hypoblast
6
Q

Formation of Extraembryonic membranes and cavities

A
  • Membranes and cavities come to surround developing embryo to provide nutrition and protection
  • They form primarily from extraembryonic tissue by a complicated process of migration and cavitation
  • By the end of the second week all of the extraembryonic membranes and cavities will be formed
  • With further development membranes fuse and cavities are lost but general organization remains
  • Amniotic cavity and amniotic membrane
    • Develope as inner mass cells reorganize to form the bilaminar disk
  • Primative yolk sac
    • lined by exocoelomic membrane
      • Exocoelomic membrane is made my the migration of hypoblast cells
  • Extraembryonic mesoderm
    • Majority forms from hypoblast (exocoelomic membrane)
    • some from epiblast during gastrulation
  • Extraembryonic Coelom
    • forms by splitting of the extraembronic mesoderm
    • Splanchnic Extraembryonic Mesoderm
      • Extraembryonic mesoderm associated with yolk sac
    • Somatic extra embryonic mesoderm
      • Exra embryonic mesoderm associated with other structures; amniotic membrane, connecting stalk, chorion
7
Q

Chorion

A
  • Somatic Extraembryonic Mesoderm
  • Cytotrophoblast
  • Syncytiotrophoblast
  • Forms fetal portion of placenta
8
Q

Allantois

A
  • Endodermally lined projection from yolk sac into the connecting stalk
9
Q

Molar Pregnancy

A
  • Abnormal embryonic development with excessive development of trophoblast – extraembryonic structures
  • Complete hydatidiform molar pregnancy
    • Excessive development of trophoblast
    • Little or no embryonic tissue
    • genome is entirely paternal
      • fertilization of oocyte, which is lacking its nucleus, either by one sperm that duplicates its DNA to form a diploid or by two sperm (with separate DNA)
    • May produce benign or malignant tumor
  • Partial or incomplete hydatidiform molar pregnancy
    • Excessive development of trophoblast
    • Some development of iner cell mass/embryonic tissue
    • Genetic analysis revealed triploidy
      • one maternal and two paternal sets of chromosomes
10
Q

Genomic Imprinting

A
  • Paternal genome drives Trophoblast
  • Maternal genome drives inner cell mass development
  • Spermatogenesis and oogenesis have different patterns of methylation of DNA
  • Molar pregnancy believe to be the result of genomic imprinting
  • Suggests non-equivalence of maternal and paternal genomes with respect to regulating extraembryonic and embryonic development
11
Q

_____ genome drives trophoblast development

A

Paternal

12
Q

_____ genome drives inner cell mass development

A

Maternal

13
Q

Incomplete or Partial Hydratidiform Molar Pregnancy

A
  • Excessive development of trophoblast
  • Some development of inner cell mas
    • Embryonic tissue
  • Genetic analysis revealed triploidy
    • one maternal and two paternal sets of chromosomes
14
Q

Complete Hydatidiform Molar Pregnancy

A
  • Excessive Development of trophoblast
  • Little or no embryonic tissue
  • Genome is entirely paternal
  • May produce benign or malignant tumor

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