embryonic development, process and formation of blastocyst

‘
]8”P{“”””””””””””””” 766667I888

DEFINITION
 Human embryology is the study of
human development during the first eight
weeks after fertilization (fusion of sperm
and oocyte).

PROCESS OF EMBRYONIC
DEVELOPMENT

2 nd - 3 rd day
Division of the zygote into two
blastomeres, it takes approximately 30
hours after fertilization.
The blastomeres continue to divide by binary
division through 4,8,16 cell stage until a
cluster of cells is formed and is called
MORULA. It will occur approximately 3
days after fertilization. The morula enters
in to the uterus cavity.

4 th day
 Shortly after the morula enters the uterine
cavity (approximately 4 days after
fertilization), the fluid from the uterine cavity
passes through the zona pellucida to form the
space. A fluid-filled space called the
blastocyst.

4 TH DAY CON…..
 ZONA HATCHING – due to the blastocyst
enlargement the zona pellucida becomes
streched, thinned and gradually disappear.
 Lysis of the zona and escape of the embryo is
called zona hatching.

5 th day
 As fluid increases in the blastocystic cavity,
it separates the blastomeres into two parts:
 A thin, outer cell layer, the trophoblast, it
develops the placenta.
 A group of centrally located blastomeres, is
called inner cell mass, which gives the
embryo; the inner cell mass is called the
embryoblast

6 – 7 DAY
IMPLANTATION NIDATION
 After entering the uterus,
the fertilized egg attaches to
the uterine lining, or
endometrium. This process
is called implantation. It
occurs nearly 6 – 7 day after
fertilization, and it
completed at 11 day after
fertilization.

GERM LAYERS
ECTODERM
ENDODERM
MESODERM

10 – 11 th day
 Some cells of the inner cell mass forms flat
and arranged in center of the blastocyst, this
cells is called as endoderm.
 The remaining cells become columnar and
forms the another layer is called as
ectoderm.
 The space between the ectoderm and
endoderm is called as mesoderm.

 A small cavity appears between ectoderm and
trophoblast. This cavity is called as amniotic cavity.
 The amniogenic cells secrete the amniotic fluid, and
amniotic cavity gradually enlarges.

12 th day
 The cells of endoderm gradually spreads over the
cavity of the blastocyst, now this cavity is called as
yolk sac.
 Now the embryo in the form of bilaminar embryonic
disc.

15 – 21 day ( 5 th week after menstruation)
FORMATION OF MESODERM
 Proliferation of ectodermal cells in the midline, leads
to formation of primitive steak.
 Cells with in the streak spreads laterally between the
ectoderm and endoderm as intra embryonic mesoderm.
 Intra embryonic mesoderm becomes continues with
the Extra embryonic mesoderm at the lateral border of
the embryonic disc.

6 th week after menstruation
Extra embryonic coelom
 Extra embryonic mesoderm separates the yolk sac
and amniotic cavity from the trophoblast.
 Small cystic spaces now appear with in the Extra
embryonic mesoderm.
 These space gradually enlarge and fuse to form
Extra embryonic coelom.

 Extra embryonic coelom separate the
trophoblast from the embryo leaving the gap in
front is known as body stalk . Later it becomes
the umbilical card.

8 TH WEEK
 The amniotic cavity become filled with amniotic fluid
gradually and it covers the blastocyst.
 The embryo freely floating on the amniotic fluid.

10 TH WEEK
 The gestational sac almost fills up the cavity of the
uterus except in the part of isthmus.
12 WEEK
 The fetal head is seen in the enlarged uterus .
 From the embryonic plate, the organs of the embryo is
developing gradually.

ORGANOGENESIS
Ectoderm Outer layer
Nervous system including brain, spinal
cord and nerves
Lining of the mouth, nostrils, and anus
Epidermis of skin, sweat glands, hair,
nails

Mesoderm Middle Layer
Bones and muscles
Blood and blood vessels
Reproductive and excretory systems
Inner layer (dermis) of skin

Endoderm Inner Layer
Lining of digestive tract
Lining of trachea, bronchi, and lungs
Liver, pancreas
Thyroid, parathyroid, thymus,
urinary bladder

DEFINITION
It starts from the eight weeks
pregnancy to till delivery of the fetus is
known as fetal development.

Fetal Period
9-12
13-16
17-20
21-38

1 MONTH  First Trimester
At the end of four weeks:
 Baby is 1/4 inch in length (0.6 cm)
 Heart, digestive system, backbone
and spinal cord begin to form
 Placenta (sometimes called
"afterbirth") begins to develop
 The single fertilized egg is now
10,000 times larger than size at
conception

MONTH 2
 First Trimester
At the end of 8 weeks:
 Baby is 1-1/8 inches long ( 2.5
cm)
 Heart is functioning
 Eyes, nose, lips, tongue, ears and
teeth are forming
 Penis begins to appear in boys
 Baby is moving, although the
mother can not yet feel
movement

MONTH 3
 First Trimester
At the end of 12 weeks:
 Baby is 2 1/2 to 3 inches long (6.3 to
7.6 cm)
 Weight is about 1/2 to 1 ounce (28 g)
 Nails start to develop and earlobes
are formed
 Arms, hands, fingers, legs, feet and
toes are fully formed
 Eyes are almost fully developed
 Baby has developed most of his/her
organs and tissues
 Baby's heart rate can be heard at
10 weeks with a special instrument
called a Doppler

MONTH
4 SecondTrimester
At the end of 4 months:
 Baby is 6 1/2 to 7 inches long (16.5 to 17.7cm).
 Weight is about 6 to 7 ounces (170 to 198g )
 Baby is developing reflexes, such as sucking
and swallowing and may begin sucking his/her
thumb
 Tooth buds are developing
 Sweat glands are forming on palms and soles
 Fingers and toes are well defined
 Sex is identifiable
 Skin is bright pink, transparent and covered
with soft, downy hair
 Although recognizably human in appearance,
the baby would not be able to survive outside
the mother's body

MONTH 5
 Second Trimester
 Baby is 8 to 10 inches long (20.3 – 25 cm)
 Weight is about 1 pound (0.45 kg or 450 g)
 Hair begins to grow on baby's head
 Soft woolly hair called lanugo will cover its body.
Some may remain until a week after birth, when it
is shed.
 Mother begins to feel fetal movement
 Internal organs are maturing
 Eyebrows, eyelids and eyelashes appear

MONTH 6 Second Trimester
 Baby is 11 to 14 inches long (27.9 – 35.5 cm)
 Weight is about 1 3/4 to 2 pounds (793 – 907
g)
 Eyelids begin to part and eyes open
sometimes for short periods of time
 Skin is covered with protective coating called
vernix
 Baby is able to hiccup

MONTH 7
Third Trimester
 Baby is 14 to 16 inches long (35.5 – 40.6 cm)
 Weight is about 2 1/2 to 3 1/2 pounds (1.13-
1.58 kg)
 Taste buds have developed
 Fat layers are forming
 Organs are maturing
 Skin is still wrinkled and red
 If born at this time, baby will be considered a
premature baby and require special care

MONTH 8
Third Trimester
 Baby is 16 1/2 to 18 inches long ( 41.9 –
45.7 cm)
 Weight is about 4 to 6 pounds (1.8 – 2.7 kg)
 Overall growth is rapid this month
 Tremendous brain growth occurs at this
time
 Most body organs are now developed with
the exception of the lungs
 Movements or "kicks" are strong enough to
be visible from the outside
 Kidneys are mature
 Skin is less wrinkled
 Fingernails now extend beyond fingertips

MONTH 9
Third Trimester
 Baby is 19 to 20 inches
long(48 – 50.8 cm)
 Weight is about 7 to 7 1/2
pounds (3.1 – 3.4 kg)
 The lungs are mature
 Baby is now fully developed
and can survive outside the
mother's body
 Skin is pink and smooth
 Baby settles down lower in
the abdomen in preparation
for birth and may seem less
active

embryonic development, process and formation of blastocyst

More Related Content

Similar to embryonic development, process and formation of blastocyst (20)

More from prakash801438 (20)

Recently uploaded (20)

embryonic development, process and formation of blastocyst