1. Lecture 1: From Fertilization to Gastrulation

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Why Embryology?
Birth defects are the leading cause of infant mortality.
Birth defects are a major contributor to morbidity, including physical and mental handicaps.
All women of childbearing age are at risk of having an infant with a birth defect. The incidence rate is 6/100 births.
Each of you will have contact with women of childbearing age; either as a friend, as a companion, or as a patient. Or you are one yourself.
MANY BIRTH DEFECTS CAN BE PREVENTED!
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1st Prenatal Visit: 8 Weeks
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The First Week
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5. From the Morula Stage to Compaction
Morula (3 Days)
Compacted Embryo
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6. Formation of the Blastocyst and Implantation
Syncytiotrophoblast
Cytotrophoblast
Blastocyst (4-5 Days)
Implanting Blastocyst (6 Days)
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Hydatidiform Moles
Formed from trophoblast
Paternal genome (genomic imprinting)
Secrete high levels of hCG (syncytiotrophoblast)
May become invasive (choriocarcinomas)
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8. First Week of Development
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9. Sites for Ectopic Pregnancies
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Tubal Pregnancy
Uterine tube
Ampullary region
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11. Ectopic Pregnancy in the Rectouterine (Douglas) Pouch
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12. Assisted Reproductive Technologies (ART)
Fertility treatments in which both the eggs and sperm are handled in the laboratory (i.e., in vitro fertilization and related procedures). Eggs and sperm are placed in a culture medium; fertilized eggs are placed in the uterus.
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ART Cycles Performed, Live-Birth Deliveries, and Live Babies Born Using ART—US,
115,392 procedures reported to CDC in 2002; 45,751 infants born after ART in US (1.1% of all births)
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14. Adverse Outcomes Potentially Associated with ART
Embryo effects
Spontaneous abortions
Multiple births
Adverse perinatal outcomes: low birth weight, preterm delivery (even among singleton births)
Birth defects
Developmental disabilities
Childhood malignancies
Longer term outcomes?
Effects on puberty/future fertility
Effects on chronic disease risk
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17. Large Meta-Analysis Study
30-40% Increased Risk of Birth Defects from ART
From: Hansen et al., Human Reproduction, 20: 328, 2005
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18. Implantation with Formation of Two Layers in the Embryoblast and the Trophoblast
Implanting Blastocyst (6 Days)
Implanted Embryo (7.5 Days)
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19. Early Trophoblast (Placental) and Embryonic Development
9 Days
13 Days
12 Days
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Extraembryonic mesoderm (Visceral layer)
(Parietal layer)
15 Days
2nd Week = Week of Two’s
Cytotrophoblast: Syncytiotrophoblast & Cytotrophoblast
Extraembryonic Mesoderm: Visceral (splanchnic) & Parietal (somatic) Layers
Embryonic Disc: Epiblast & Hypoblast
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Formation of the Primitive Streak and Establishment of the Cranial-Caudal Axis
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22. Anterior Visceral Endoderm (AVE) Induces the Cranial Region
BMPs: Hatched area = ventral mesoderm (kidneys and body wall) and ectoderm
BMPs (goosecoid, brachyurea T) = dorsal mesoderm (somites) and neural ectoderm
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Overexpression of Goosecoid in Frogs Causes Double-Headed Tadpoles: Does It Cause This Defect in Humans?
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24. Genetic Regulation of Laterality
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Situs Inversus Kartagener syndrome (20%) Cilia malfunction with situs inversus (bronchiectasis and sinusitis) Laterality Sequences Left or right sidedness Asplenia (right) Polysplenia (left)
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26. Gastrulation: Formation of the 3 Germ Layers
14 Days
16 Days
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During Gastrulation, Epiblast Cells Move Toward the Primitive Streak, Leave the Epiblast, and Create 2 New Layers
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28. Formation of the Prechordal Plate and Notochord
Cranial
Caudal
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29. Formation of the Notochord
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The Three Germ Layers
Mesoderm
Endoderm
Notochord
(Part of the mesoderm)
Ectoderm
Ectoderm: skin, CNS, PNS, eyes, internal ear, neural crest cells (bones and connective tissue of the face and part of the skull)
Mesoderm: bones, connective tissue, urogenital system, cardiovascular system
Endoderm: gut and gut derivatives (liver, pancreas, lungs, etc.)
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