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• 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 Division1…2 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.

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

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

• 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?