Embryology Flashcards
embryology
developmental events that occur prior to birth
cell differentiation
transformation into specific cell types
cell development
process by which cells become fully functional (maturation)
prenatal period
first 38 weeks of human development
three developmental stages
- pre-embryonic period
- embryonic period
- fetal period
- pre-embryonic period
-first two weeks after fertilization of egg
-formation of blastocyst
-ends with implantation in lining of uterus
- embryonic period
-3rd through 8th weeks
-all major organ systems begin to develop
- fetal period
-9th through 38th weeks (birth)
-growth and development continues
-ends at birth
what are the mitotic divisions of a zygote called
cleavage
zygote
fertilized egg
once the zygote reaches the 16-cell stage, what is it called?
morula
after the morula enters the uterine cavity, what does it become?
blastocyst
2 components of blastocyst
trophoblast and embryoblast
trophoblast
outer ring of cells that will develop into the chorion (placenta)
embryoblast
cluster of tightly packed cells inside the blastocyst that will form the embryo
pluripotent
can differentiate into any cell type in the human body
how long until the blastocyst enters the uterus?
one week
what layer does the blastocyst enter first
endometrium (lining of uterus)
by day 9, what has the blastocyst done?
completely burrowed into the uterine wall
By day 8, cells of the embryoblast differentiate into two distinct types:
- hypoblast
- epiblast
hypoblast
layer of small cuboidal cells facing the blastocyst cavity
epiblast
layer of columnar cells deep to the hypoblast
together, the two layers of the embryoblast form a flat disc called the
bilaminar germinal/embryonic disc
Extraembryonic membranes
- Yolk sac
- Amnion
- Chorion
Yolk sac
Serves as a site for early blood cell and vessel formation (attached to hypoblast); where blood cells initially develop
Amnion
Thin layer of cells that forms above and is derived from the epiblast
Amniotic cavity
Fluid filled cavity that appears between the amnion and epiblast layer
Chorion
Outermost membrane responsible for formation of the placenta
Placenta
Highly vascularized organ that serves as an interface between embryo or fetus and mother
Embryonic portion of the placenta is the…
chorion
Functions of placenta
-Exchange of nutrient between embryo and mother
-production of estrogen and progesterone to maintain uterine lining
What does the embryonic period start
Establishment of 3 primary germ layers
Gastrulation
Process by which cells from the epiblast migrate to form the primary germ layers (week 3); becomes 3 layered structure
Gastrulation starts with
Formation of the primitive streak
Primitive node
Cephalic end of the primitive streak
Primitive pit
Depression in primitive node
Three primary germ layers
-endoderm
-ectoderm
-mesoderm
Structure is called an embryo when
Three primary germ layers are present
Invagination
Inward movement of cells from epiblast layer through primitive streak between epiblast and hypoblast layers
Epiblast turns into…
ectoderm
Other migrating cells displace the hypoblast and become the
Endoderm
All three germ layers are derived from the
Epiblast
Formation of the neural tube begins with the appearance of the
Notocord
Notocord
-derived from mesoderm
-important signaling structure
Neurulation
The formation of the neural tube from overlying ectoderm cells
The neural tube will develop into the
Central nervous system
Cehalocaudal folding
Head and tail folding
Transverse folding
Lateral folding
Teratogens
Any agents that can cause congenital malformations (birth defects)
Ectoderm consists of
Covering and lining; skin
Mesoderm becomes
Bones and muscles
Endoderm becomes
Innermost linings; digestive tract, bladder, liver, etc
Organogenesis:
Organ development
-rudimentary forms of most organ systems are complete by the end of the embryonic period (week 8)
