The document provides information about embryology and the development of the fetus and placenta from weeks 4-8 of gestation. It defines embryology and describes key events like fertilization, implantation, trophoblast formation, villi development, and placenta formation. It discusses the formation of the embryo, amnion, and body stalk, as well as developmental changes that occur each week such as elongation of the embryo, formation of the circulatory system, development of the hands and feet, and the embryo taking on more human characteristics.

1. MITTAL COLLEGE OF NURSING, AJM
SUBMITTED TO :-. SUBMITTED BY:-
SNEHALATA PARASHAR. GAGANDEEP
KUMAWAT

2. A PRESENTATION ON
Embryology
Development of fetus and
placenta

3. DEFINATION
Embryology is the branch of biology that
studies the prenatal development of
gametes, fertilization, and development
of embryos and fetuses. Additionally,
embryology encompasses the study of
congenital disorders that occur before
birth, known as teratology

11. FERTILIZATION

30. IMPLANTATION

43. TROPHOBLAST
•Trophoblast is the outer cell mass which
forms the placenta and chorion

51. WHEN
When the interstitial implantation is
completed on 11th day ,the blastocyst is
surrounded on all side by lacunar spaces
around cord of syncytial cells, called
trabeculae

52. VILLI
•The finger like buds are called primary
stem villi surrounded by lacunar spaces
which will later form into intervillous
space.
•After the appearance of the primitive
mesenchyme and the development of the
chorion the primary stem villi are named
chorionic villi

53. PLACENTA
•As the growth of embryo proceeds decidua
capsularis become thinner beginning at 6th
week
•Villi and lacunar spaces in the embronic area
get obliterated converting the chorion into
chorion leave
•This is compensated (a) exuberant growth
and proliferation of the decidua basalis (b)

54. PLACENTA.
•These two chorion frondosum and
decidua. Basalis form the discrete
placenta .It begins at 6th week and
complete by 12th week

56. EMBROBLAST
•Embyroblast is the inner cell mass which
forms the fetus , amnion and umbilical
cord

61. EXTRAEMBRYONIC COELOM
•Extraembryonic mesenchyme. Derived
from the trophoblast appear to separate
the yolk sac from the blastocyst wall and
also the amniotic cavity from the
trophoblast of chorion.Small cystic space
(lacuna) now appear with in the
extraembryonic mesenchyme these space
gradually enlarge and fuse to form

62. BODY STALK
•Progressive enlargment of extraembryonic
coelom separate the amnion from the
inner aspect of the chorion except the
caudal end of the Embro. There the
mesenchymal attachment persists to form
body stalk . Umbilical cord develops from
this body stalk

76. 4TH WEEK OF DEVELOPMENT
•The embryo grows dramatically during the
fourth week. It more than triples its length
to 3.5mm and its weight approximates 5
mg.

77. 4TH WEEK OF DEVELOPMENT
•Elongation of the embryo has occurred,
and it has become curved pon itself with
the formation of a head and tail fold.
Lateral body folds develop making the
embryo tubular rather than flat and disc
shaped. Closure of the neural tube begins
in the area of the occiput and proceeds
upward and downward from that point.
Somites formed in a craniocaudal
sequence as the neural tube closes, can

78. 5TH WEEK OF DEVELOPMENT
•The intestinal system is formed from the
yolk sac, and differentiation of the buds,
which will become the oesophagus,
stomach, liver and pancreas, is
progressing. The thyroid and thymus
glands are also developing. The primitive
circulatory system is established, and the
heart is beating. The budlike projections
on the surface of the embryo are the

79. 6TH WEEK OF DEVELOPMENT
•The head has become larger than the trunk
and is bent over the heart prominence.
Elevations in the facial ectoderm are evident
and the position of the eyes, nose, mouth,
and the groove that is to become the external
acoustic meatus is established. In the upper
limbs, the elbows and wrists are identifiable,
and the hand plates develop ridges called
finger rays. The lower limbs are not developed
to the same degree. Changes are beginning to

80. 7TH WEEK OF DEVELOPMENT
•Cerebral hemispheres appear as the head
enlarges rapidly. The eyes move from a lateral to
a more frontal position as the face elongates.
Prominences appear over the ventral body wall
from early because their function is vital to the
maintenance and survival of the embryo. As the
embryo continues to grow, the umbilical cord
shrinks. The arm and hand of the upper limbs
and the high, leg, and foot segments of the lower
limbs become apparent The fingers develop, the
their growth is critical at this point (40 to 50
days). The CRL is 14 to 20 mm; the weight is 400

81. 8TH WEEK OF DEVELOPMENT
•During this final week of the embryonic
period, the embryo exhibits definite human
characteristics. The cerebral hemispheres
have grown so rapidly that the head now
makes up 50% of the mass of the embryo. The
face occupies the lower half of the head, and
the eyes continue to move to a more frontal
plane. Eyelids folds develop. These will
become fused during the ninth week and