Introduction to Embryology

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Introduction to Embryology

• Carolyn Joy Rodgers MD FACOG

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AIM

• Begin your study of embryology
• Outline the early major developmental events and
  anatomical landmarks of a human embryo
• Understand and be able to use the terminology of
  early human development
• Act as an introduction to the systems embryology
  you will encounter in the phase one modules
• Begin to identify relevance of these processes to
  clinical practice

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Learning Outcomes lecture one

• Describe simply the processes from fertilisation
  to implantation
• Describe simply the second week of human
  development
• Describe simply the early stages of placental
  development

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What is embryology?

• Development from single diploid cell. to.
• Multicellular organism
• Organised body structure
• Specialised tissues

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Development

• Growth
• Morphogenesis
• Differentiation

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Role and relevance of embryology

• Understand normal body structure
• Maturation of adult structures
• Anatomical relationships
• Links prenatal development to clinical medicine
• Values in medicine

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How is it studied?

• Starting with anatomy
• Teratology
• Experimental
• Molecular / Cellular
• Genetic

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The embryonic period

• Conception
• Eight weeks
• Body axes
• Organ primordia
• Three layers
• Early placenta

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First Week

• Fertilisation
• Cleavage
• Blastocyst formation
• Implantation

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The first day

• Gametes and fertilisation-zygote
• A unique new individual
• Ampulla
• Cleavage
• Blastomeres

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Day 3

• Compaction
• Morula

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Entering the uterus day 4-5

• Blastocoele / Blastocyst
• Outer cells-Trophoblast-
• Inner cell mass-embryoblast -pluripotent

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Implantationday 6-7

• Hatching
• Cytotrophoblast
• Syncytiotrophoblast
• Invasion

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Implantation processday7

• Uterus has been prepared
• Usually in upper part of uterus
• Specific orientation and maternal/embryonic
  communication mechanisms
• Immunologically complex
• Very little information in humans
• IVF- most likely stage of failure

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Second week

• Two layers
• Amniotic cavity
• Yolk sac
• Extraembryonic mesoderm-splanchnic
• -
  somatopleural

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The two layers Bilaminar disc day8-9

• Epiblast and hypoblast
• Amniotic cavity
• Primitive yolk sac

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Day 10-12

• Utero-placental
• circulation
• Extra-embryonic
• mesoderm
• Chorionic cavity
• (Extra-embryonic coelom)

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Day 13-14

• Implantation bleed
• Human chorionic gonadtrophin HCG
• Villous formation
• Secondary yolk sac
• Chorionic plate
• Connecting stalk