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 Division 1…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. 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 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?