Copyright © 2010 Wolters Kluwer Health | Lippincott Williams & Wilkins Lecture 1: From Fertilization to Gastrulation

Copyright © 2010 Wolters Kluwer Health | Lippincott Williams & Wilkins

Lecture 1:From Fertilization to

Gastrulation


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!


1st Prenatal Visit: 8 Weeks


The First Week


From the Morula Stage to Compaction

Morula (3 Days) Compacted Embryo


Formation of the Blastocyst and Implantation

Blastocyst (4-5 Days) Implanting Blastocyst (6 Days)

Syncytiotrophoblast

Cytotrophoblast


Hydatidiform Moles

• Formed from trophoblast

• Paternal genome (genomic imprinting)

• Secrete high levels of hCG (syncytiotrophoblast)

• May become invasive (choriocarcinomas)


First Week of Development


Sites for Ectopic Pregnancies


Tubal Pregnancy


Ectopic Pregnancy in the Rectouterine (Douglas) Pouch


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.


ART Cycles Performed, Live-Birth Deliveries, and Live Babies Born Using ART—US, 1996-2002

115,392 procedures reported to CDC in 2002; 45,751 infants born after ART in US (1.1% of all births)


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


0

20

40

60

80

100

120

LBW VLBW Preterm

% a

dv

ers

e p

eri

na

talo

utc

om

es

Singletons Twins Triplets +

Percentage of Adverse Perinatal Outcomes among ART Infants by Plurality -- US, 2002


Percent LBW among ART singletons (1996-1997) compared to all singleton births to

non-teen mothers in US (1997)

13.2

2.6

5.7

1

0

5

10

15

LBW VLBW

Per

cen

t

ART

USPopulation

Schieve et al., N Engl J Med 346:731-7, 2002


Large Meta-Analysis Study

30-40% Increased Risk of Birth Defects from ART

From: Hansen et al., Human Reproduction, 20: 328, 2005


Implantation with Formation of Two Layers in the Embryoblast and the Trophoblast

Implanting Blastocyst (6 Days) Implanted Embryo (7.5 Days)


Early Trophoblast (Placental) and Embryonic Development

9 Days

12 Days

13 Days

Yolk sac cavity

Oropharyngeal

membrane


15 days15 Days

2nd Week = Week of Two’s

Cytotrophoblast: Syncytiotrophoblast & Cytotrophoblast

Extraembryonic Mesoderm: Visceral (splanchnic) & Parietal (somatic) Layers

Embryonic Disc: Epiblast & Hypoblast

(Parietal layer)

Extraembryonic

mesoderm (Visceral layer)


Formation of the Primitive Streak and Establishment of the Cranial-Caudal Axis


BMPs: Hatched area = ventral mesoderm (kidneys and body wall) and ectoderm

BMPs (goosecoid, brachyurea T) = dorsal mesoderm (somites) and neural ectoderm

Anterior Visceral Endoderm (AVE) Induces the Cranial Region


Overexpression of Goosecoid in Frogs Causes Double-Headed Tadpoles: Does It Cause This Defect in Humans?


Genetic Regulation of Laterality


Situs Inversus Kartagener syndrome (20%) Cilia malfunction with situs inversus (bronchiectasis and sinusitis)

Laterality Sequences Left or right sidedness Asplenia (right) Polysplenia (left)


Gastrulation: Formation of the 3 Germ Layers

14 Days 16 Days

Oropharyngeal membraneOropharyngeal

membrane


During Gastrulation, Epiblast Cells Move Toward the Primitive Streak, Leave the Epiblast, and Create 2 New Layers

Oropharyngeal membrane


Formation of the Prechordal Plate and Notochord


Oropharyngealmembrane


Formation of the Notochord

A

Cut lines for C B



The Three Germ Layers

Mesoderm

EndodermNotochord (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.)

Documents

Copyright © 2010 Wolters Kluwer Health | Lippincott Williams & Wilkins Lecture 1: From Fertilization to Gastrulation