Transcript Fertilization and Development

Fertilization and Development
Fertilization
 The union of sperm and ovum
– Forms a zygote
 The ovum completes meiosis II following fertilization
 After fertilization, chemical reactions occur preventing
additional sperm from entering the ovum
Early Development
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Morula
Inner cell mass
 A fertilized egg is a zygote
 The zygote divides (mitosis)
to become a morula (solid
ball of cells)
 The morula hollows out to
become a blastocyst
 The inner cell mass
undergoes gastrulation to
form a tube with three layers
– The developing embryo is now
called a gastrula
Early Development
Implantation
of the
blastocyst
into the
uterine wall
Primary Germ Layers
 Layers are formed by
differentiation of cells
 Ectoderm (outside)
– Skin
– Brain and spinal cord
 Mesoderm (middle)
– Muscle
– Bones
– Blood
 Endoderm (inside)
– Lungs
– Digestive tract
– Liver
Multiples
Twins
 Dizygotic = Two zygotes
– Two sperm fertilized two separate eggs
– Occurs when 2 oocytes are ovulated
– These twins are as alike as any other siblings
 Monozygotic = One zygote
– Genetically identical
– 3 different types depending on where the split
occurs
3 Types of Monozygotic Twins
From Embryo to Fetus
 At 3-4wks the neural tube forms
– The neural tube will form the brain and spinal cord
– All other organs organize around the neural tube
 At 8 weeks, the embryo becomes a fetus
– All of the rudimentary features are formed
Life’s Greatest Miracle