Download Fertilization Notes #2

FERTILIZATION
& DEVELOPMENT--#2
Prenatal
Development
GESTATION
• Definition: period of time between
fertilization and birth
• Typically lasts 38 weeks or 9 months
STAGES OF DEVELOPMENT
• Fertilization of the egg occurs forming a
structure called a zygote
• After the zygote divides into two cells it is
called an embryo
• After 3 days, mitotic divisions occur
resulting in a 16 cell structure, then
eventually a structure of 32 cells
AFTER 5 DAYS
• a solid ball of cells, or
morula, develops and
the embryo attaches to
the uterus
CONTINUED MITOSIS
• division continues
until the center of the
ball becomes hollow
forming the blastula
GASTRULATION
• The blastula pushes inward on one
side, resulting in the formation of a 2layered gastrula
the inner layer is called the
endoderm
the outer layer is called the ectoderm
FROM 2 to 3 LAYERS
• Eventually, a third cell
layer, or mesoderm will
form
Diagram
WHAT NEXT??
•
The embryonic cells specialize to perform the
various tasks of particular tissues throughout
the body, a process called differentiation
The 3 cell layers will form the following:
1. Ectoderm--outer skin, nervous system
2. Endoderm--lining of digestive tract, respiratory
tract, portions of liver and pancreas
3. Mesoderm--muscles, gonads, and the
circulatory, skeletal, excretory systems
DIAGRAM
Diagram