Human Embryology

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Human Embryology
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Fertilization

• Fertilization- results in a zygote
• -requires the sperm egg nucleus to fuse

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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

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Egg Structure

• Egg structure contains 3 parts
• -plasma membrane, vitelline envelope, jelly coat

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Fusion of egg and sperm
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Female Reproductive System
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Fertilization Process

• 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

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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

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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

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Fertilization of female egg
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• Development- all the changes that occur during
  the life of an organism
• Embryo- 1st stages of development of an organism
  after the zygote forms

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Cell Division12 buckle my shoe

• 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.

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Deuterostomes vs. ProtostomesSAY 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

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Protostomes

• protostomes (clams, worms, insects) undergo
  spiral cleavage- cells divide and they do not sit
  on top of each other they appear to spiral

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Morula

• The eight cells now continue to divide until you
  are simply a large solid ball of cells (16-32
  cells).

Morula
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Blastula

• 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.

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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..

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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.

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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

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What do the 3 layers become?