Human Embryology
Fertilization
• Fertilization- results in a zygote
• -requires the sperm & egg nucleus to fuse
Sperm Structure
• Sperm- made of 3 parts
• head- contains haploid nucleus & acrosome
(enzymes that allow sperm to penetrate the egg)
• middle piece- contains mitochondria (make
energy; ATP)
• tail- flagellum- allows sperm to swim toward the
egg
Egg Structure
• Egg structure contains 3 parts
•
-plasma membrane, vitelline envelope,
jelly coat
Fusion of egg and sperm
Female Reproductive System
Fertilization Process
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Acrosome enzymes of sperm digest
away the jelly coat
Acrosome extends a filament that
attaches to a receptor on vitelline
envelope (like a lock & key)
Nuclear membrane of sperm & plasma
membrane of egg fuse
Fertilization Process (cont.)
• Sperm nucleus enters the egg
• Zygote forms when sperm nucleus & egg
nucleus fuse
• Following fusion, the egg plasma
membrane & vitelline envelope undergo
changes that prevent the entrance of other
sperm
• Vitelline envelope becomes the fertilization
envelope
Fertilization Process
• After egg is released from the ovary it
moves into the fallopian tube and waits for
the arrival of the sperm and fertilization to
take place
• Then wave-like action of cilia move the
fertilized egg toward the uterus for
implantation to take place
Fertilization of female egg
• Development- all the changes that occur
during the life of an organism
• Embryo- 1st stages of development of an
organism after the zygote forms
Cell Division
1…2 buckle my shoe
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Embryonic Development (Continued)
-zygote undergoes cleavage (cell division w/o
growth)- mitosis and DNA replication occur
repeatedly
Once the zygote is formed it begins to divide
through a process called cleavage.
Upon completion of the first division, you have
two cells. Then these two cells divide to form
four cells.
Deuterostomes vs. Protostomes
SAY WHAT???
• 8-CELL STAGE IS KEY DIFFERENCE!!!Deuterostomes- (starfish & vertebrates)
cleavage results in 8 cells sitting directly on
top of each other. This is called radial
cleavage
Protostomes
• protostomes (clams, worms, & insects)
undergo spiral cleavage- cells divide and they
do not sit on top of each other; they appear
to spiral
Morula
• The eight cells now continue to divide until
you are simply a large solid ball of cells
(16-32 cells).
Morula
Blastula
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At this time, the morula begins to form a
hollow ball of cells called the blastula.
The blastula contains a fluid filled space
known as the blastocoel.
Gastrula
• Now gastrulation occurs. The hollow ball of cells
known as the blastula begins to fold inward on
one side
• (imagine that you had a deflated basketball and
pushed it in on one side).
• When the folding occurs, it begins to create a
horse shoe shaped structure that is 2 cell layers
thick..
Gastrula (cont.)
• The outer layer of the ball is called the
ectoderm. The inner layer of the ball is called
the endoderm.
• Eventually, another cell layer will begin to form
between the endoderm and ectoderm. This
layer is called the mesoderm.
• The point where the horse shoe almost touches
is called the blastopore (small hole).
• In protostomes this will eventually form the
mouth.
• In deuterostomes this will form the anus.
3 tissue layers
• Ectoderm- forms nervous system & outer
layer of skin
• Mesoderm- forms muscle, bone, &
cardiovascular system
• Endoderm- organs of digestive system,
lining of respiratory system &
bladder
What do the 3 layers become?