General Embryology
General Embryology
General Embryology
SIGNIFICANCE OF EMBRYOLOGY
-Gives knowledge concerning beginning of human
life and changes occurring during prenatal
development.
-Understanding normal post-natal growth and
development of various craniofacial abnormalities
Period of ovum- fertilization to 2 weeks
Period of embryo – 2nd to 8th week
Period of fetus - 9th week to term
Imp-week 4-8,teratogens
He who sees things grow from the
beginning will have the finest view of
them……..
-ARISTOTLE
Day 0
FERTILIZATION
Cleavage
blastomeres
morula
2 cell 4 cell 8 cell
FORMATION OF BLASTOCYST Day 4-7
As morula enters uterus, a fluid-filled space called
blastocyst cavity appears in morula.
As fluid increases, it separates blastomeres into two
parts:- Outer cell layer, Trophoblast.
-Inner cell mass, which act as primordium of
embryo called Embryoblast
Implantation
The syncytiotrophoblast
release proteolytic
enzymes which promotes
proteolysis and invasion
of maternal endometrium..
Day 8
DAY 9
Isolated cavities
called lacunae
appear in
syncytiotrophoblast
Adjacent lacunae
fuse to form lacunar
networks
Capillaries around
embryo become
dilated to form -
sinusoids
DAY 9
The blastocyst is more deeply embedded in the
endometrium, and the penetration defect in the
surface epithelium is closed by a fibrin
coagulum (Fig. 4.3).
Uteroplacental circulation.
CLINICAL RELEVANCE
Soon the inner cell mass form 2 types of cells which lie Between
these 2 cavities
Epiblast: High columnar cells related to amniotic cavity.
Hypoblast – squamous or cuboidal cell mass adjacent to
primary yolk sac
Proliferation of
cytotrophoblastic cells
into syncytiotrophoblast
leads to Formation of
primary chorionic villi
(later forms placenta).
DAY 13
DAY 14
2 processes occur
simultaneously:
Formation of
extraembryonic somatic
and splanchnic mesoderm
due to split of
extraembryonic mesoderm
by extraembryonic coelom.
Extraembryonic coelom is
now called chorionic cavity.
DAY 14
NEURULATION.
GASTRULATION:
Various
cellular events take place in the
notochordal process which give rise to the
NOTOCHORD.
IMPORTANCE OF NOTOCHORD:
Defines primordial axis of embryo and gives
rigidity.
Serves as basis for development of axial
skeleton (bones of head and vertebral column).
Indicates future site of vertebral bodies.
NEURULATION DAY 19,20