Germinal, Embryonic & Fetal Stage

germinal stage

period from conception to implantation (approximately 2 weeks)

Zygote

begins to divide within 36 hours of conception

embryonic disk

Two distinct layers in the inner part of blastocyst

trophoblast

Outer part of the blastocyst differentiates into four membranes

miscarriage

One-third of all pregnancies result in

abnormalities in development

miscarriage usually stems from

Prior to implantation

the dividing cells are nourished by the yolk of the original egg.

Embryonic stage

begins with implantation 3rd week through the 8th week

Developmental trends

cephalocaudal and proximodistal

Cephalocaudal

head takes precedence over lower parts of the body

Proximodistal

central axis of body outward

Embryonic Disk Layers

endoderm, mesoderm, ectoderm

Ectoderm

Outer layer develops into nervous system, sensory organs, nails, hair, teeth, and outer layer of skin

Endoderm

Inner layer forms the digestive and respiratory systems, liver, and pancreas

Mesoderm

middle layer develops into the excretory, reproductive and circulatory system, muscles, skeleton, and inner layer of skin

Neural tube

develops into the brain and spinal cord

Fetal Stage

9 weeks / 3 month through birth