Embryology

prenatal period

period before birth

first 38 weeks of human development

pre-embryonic period

first two week after fertilization of egg

formation of blastocyst

ends with implantation in lining of uterus

right after conception

embryonic period

third through eighth weeks

all major organ systems begin to develop

fetal period

ninth through thirty eighth weeks

growth and development

ends at birth

zygote

fertilized egg

Week 1

zygote undergoes a series of mitotic divisions (cleavage)

morula is formed

morula enters uterine cavity and becomes blastocyst

morula

solid mass of cells

trophoblast

outer ring of cells that will develop into the chorion

outer shell

embryoblast

cluster of tightly packed cells inside of side of the cell

forms the embryo

inner cell mass

pluripotent: can differentiate into any cell type

implantation

blastocyst enters uterus

invades superficial layer of endometrium

burrows completely into uterine wall