Transcript 13-3_Development.ppt

Embryonic
Development
Fertilization
• Each month an egg matures
and is released from the
ovary during ovulation.
• The egg enters the fallopian
tube.
• It is in the fallopian tube
where sperm must
encounter the egg.
• Sperm fuses with the egg in
a process called
fertilization.
http://www.daviddarling.info/images/Fallopian_tube.gif
Early Development
• The fertilized egg is
called a zygote.
• The zygote begins to
undergo mitotic cell
division called cleavage.
• Eventually a ball of cells
called a morula is
formed.
http://www.biology.iupui.edu/biocourses/n100/images/38cleavage.jpg
The Blastula Stage
• After the 5 days
the morula has
continued to
undergo cell
division and
forms a hollow
ball of cells
called the
blastula (aka
blastocyst)
http://www.ehponline.org/members/2006/114-11/blastocyst.jpg
Implantation
• When the blastula
reaches the uterus it
becomes embedded in
the uterine lining.
• This is called
implantation and
signifies the beginning
of pregnancy.
http://www.dkimages.com/discover/previews/940/674676.JPG
Gastrulation
• Gastrulation involves the inward migration of
cells of the blastula.
• This in-folding creates a layered structured
called the gastrula.
• Some migratory cells break off and form a
third layer of cells.
• The three layers of cells are called germ
layers and will eventually form certain
organs.
http://trc.ucdavis.edu/biosci10v/bis10v/week10/gastrulation.gif
The Germ Layers
• The inner layer
is called the
endoderm.
• The middle
layer is the
mesoderm.
• The outer layer
is the
ectoderm.
Germ Layer Fate
Germ Layer
Fate
Endoderm
Becomes the digestive tract
and associated organs
Mesoderm
Becomes the muscles and
bones
Ectoderm
Becomes the skin and
nervous system