The document discusses the stages of early human development from fertilization through the 8th week. It describes the key events and changes that occur each week, including fertilization and cleavage of the zygote, formation of the blastocyst and implantation, gastrulation and formation of the three germ layers, development of the notochord and neural tube, somite formation, and the morphological changes that cause the embryo to fold from a disc to a cylinder as the major organs and body cavities begin to form. By the 8th week, the fetus is recognizably human-like and all major organs have developed.

1. PRESENTED
BY
Dr AKHIL.H.S (dept of SHAREERA RACHANA)
ALVAS AYURVEDIC COLLAGE , MOODBIDRI

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So is a process of the descent of various
components of the body. This process involves the
following factors without which a healthy can’t be
obtained. It includes spermatogenesis, oogenesis,
formation of embryo and its complete growth and

4. ROLE OF
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IN GARBHA VRUDHI
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8.  In charaka shareera it is mentioned that the fetus
gets its nourishment in different ways at different
stages of growth.
 Either in the initial stages or before
differentation of various organs it get its
nourishment from ahara rasa of the mother
through upa sneha and upa sweda (diffusion and
osmosis ). After the body parts are formed it gets
its nutrition through upasneha and nabhi nadi or
umbilical cord.
 The nabhi nadi is attached to the rasa vaha
nadi of the mother and this carries ahara rasa
veerya from the mother to the fetus. The fetus
grows by the indirect supply of nutrition.

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In cha sa 2/ 12 , atreya answer to sishyas regarding the
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15. FERTILIZATION
CLEAVAGE OF THE ZYGOTE
FORMATION OF BLASTOCYST
IMPLANTATION

16. FERTILIZATION
 It is the process by which male and
female gamates fuse to form zygote, it
occurs in the ampullary region of uterine
tube.

18. RESULTS OF
FERTILIZATION
 Sex determination.
 Starting of cleavege.

20. Two days after fertilization, embryo is at
2celledstage.
Three days after fertilization embryo
. becomes morula.
Fourth day -- Blastocyst has formed.

21. Late implantation/Uteroplacental circulation
Bilaminar disk, amniotic cavity and primary yolk sac
Extra-embryonic mesoderm and coelom
Formation of the chorion and definitive yolk sac

22. Trophoblast
Bilaminar
embryonic disc
cytotrophoblast
Epiblast
Syncytiotrophoblast
Hypoblast
Cavities
Amnionic
Blastocoel

23. EARLY 2ND WEEK
Fibrincoagulum
Lacunar stage
Exocoelomic memb
Primary yolk sac

24. 11th 12th day
Uteroplacental
 Sinusoids circulation.
Trophoblast have lacunar
space in the form of inter
communicating
network.More evident at
embryonic pole.
The cells of
synciotropoblast continue
penetrating deep and erode
endometrial lining of
meternal capillaries.
Lacunae continue with the
sinusoids.

25. Extra-embryonic
mesoderm / Extra-
embryonic coelom
Cells derived from the primitive ectoderm fill the space
between the trophoblast and two cavities
 This loose connective tissue, the extraembryonic
mesoderm, completely surrounds the amnion and
primary yolk sac
 Fluid-filled spaces appear in the mesenchyme,
pushing aside the mesenchyme to form a coelom
 These spaces fuse to form a fluid-filled cavity
completely surrounding the amnion and yolk sac,
except at the connecting stalk

26.  Extra embryonic coelom / Chorionic cavity.
 When EEC enlarges EEM will be restricted
to lining.
 Extra embryonic somato pleuric mesoderm
 Extra embryonic splanchno pleuric
mesoderm

28. Primary villi.
Secondary yolk sac
Exocoelomic cyst
Connecting stalk
13th day

30. Gastrulation: Primitive Streak and Cell Migrations
Results of Gastrulation: Fate of the Germ Layers
Notochord: the Primary Inducer
Neurulation: Neural Tube Formation
Neural Crest Cells and their Derivatives

31. GASTRULATION
 Its the process that establishes all 3 germ
layers. It begins with formation of Primitive
Streak on surface of epiblast.
 Cephalic end- primitive node.
 Cells of epiblast migrate towards primitive
streak and it become flask shape.
 It then detach from epiblast and slip beneath it.
INVAGINATION.
 Once cells invaginated, some displace
hypoblast and form- embryonic ENDODERM.
 Some lie in b/w epiblast and new embryonic
endoderm to form MESODERM.
 Remaining cells form embryonic ECTODERM.
 Thus epiblast is source of all 3 layers.

32. NOTOCHORD
 The pre notochordal cells invaginating in
the primitive streak, move forward
cranially, untill they reach prechordal
plate.
 These cells intercalate in endoderm as
notochordal plate.
 By further development, the plate
detaches from endoderm and a solid
cord is formed.
 This will serve as basis of axial skeleton.

33. NEURULATION.
 At beginning of 3rd week ectodermal germ layer is
of disc shape.
 The overlying ectoderm thickens and form NEURAL
PLATE.
 Cells of the plate make up neuroectoderm.
 Once induction begin the neural plate expands
towards primitive streak.
 By end of 3rd week,lateral edge of neural plate
expands to form NEURAL FOLD.
 And mid region – NEURAL GROOVE.
 Gradually Neural folds approaches each other and
fuse
in middle ,and continues upward and downwards.
 NEURAL TUBE.
 CRANIAL NEUROPORE & CAUDAL
NEUROPORE.

34.  Vasculogenesis- EEM – angioblasts-
angiogenic clustor of cells- endothelial
cells – this fuse with each side to form
small blood vessels.
 Hematopoiesis- occur in EEVM –
angioblasts in angiogenic cell clusters
give rise to primitive blood cells.
 At 5th week it is taken over by organs.

35. Somite development
Intraembryonic coelom & body cavities
Head-tail folding
Lateral folding

36.  In week 4, the embryo undergoes major
morphological changes as it changes from
a trilaminar disc-shaped embryo to a
cylindrical embryo.
 This is also an important week in terms of
determining placement of future organs.
 Following median and horizontal folding,
many organs and body cavities will begin
to form or will be repositioned.
 Embryo begin to fold.

37. Head-Tail Folding
 Due to the rapid growth in the median
plane of the brain, amniotic cavity, and
somites, the embryo elongates, with its
head and tail ends folding under.
 At the cranial end, the head will be folded
under, with a very prominent forebrain.
 On the ventral side, the newly positioned
primitive heart, pericardial cavity, septum
transversum, and bucco-pharyngeal
membrane

38.  At the same time that head-tail folding is
occurring, lateral folding is also
occurring to form a cylindrical embryo

39.  22nd – 23rd day – Fusion of neural fold .
Neoropores widly opened.
Heart tube begin to fold.
24th -25 th day – Cephalocaudal folding.
Cranial neuropore closing.
Optic vesicles appear.
Otic placcodes appear.
 26th-27th day – Caudal neuropore closing.
Upper limbs buds appear.
3 pairs of visceral arches.

40. EMBRYO AT 4TH WEEK.

41. Somite Development
 The paraxial mesoderm will develop into paired
cuboidal bodies, or somites (soma, body).
 These will eventually develop into the bones
(Sclerotome), Muscles (Myotome), and Dermis
(Dermatome) of and surrounding the axial skeleton
 Somites appear as bumps on the dorsal surface of the
embryo.
 At the end of week 3, 4-12 somites are present (visible
on the dorsal surface of the embryo). By the end of
week 5, 42-44 can be counted.
 The most appear between days 20-30, giving this
period the title of the somite period of development.
 Somites appear cranially to caudally, beginning at the
occipital end. They can be counted and are used to
roughly estimate the age of the embryo

42. FATE OF GERM LAYERS
 ECTODERM
This layer gives rise to:
 the central nervous system;
 the peripheral nervous system;
 the sensory epithelium of the ear, nose and
eye;
 the epidermis, hair and nails; and
 the subcutaneous, mammary and pituitary
gland; ·
 the enamel of teeth.

43. MESODERMAL SHEATH
Intermediate
Paraxial mesoderm mesoderm
Lateral plate
Nephrotomes-
cranially
Nephrogenic somatic (parietal
Somites ( 42-44) cells-caudally
The epithelial cells forming the somites lose
their epithelial shape and migrate in the splanchnic
direction of the notochord and the spinal
cord to form the sclerotome (future
(visceral
vertebral column). The dorsal wall of the
somite differentiate into
the myotome (furute muscles) and
thedermatome (future dermis). , both developing into the
excretory units of kidneys,
gonads, ducts and accessory glands

44.  ENDODERM
it provide epithelial lining of gastro-
intestinal tract, respiratory tract, urinary
tract, urinary bladder, also paranchyma
of thyroid, parathyroids, liver, pancreas.

45. 5TH WEEK
 28th- 30th day-Fourth visceral arch will be
formed.
Hind limb bud appear.
Otic vesicle and lence
placode become clear.
 31st-35th day- forelimb paddle shaped.
Nasal pit formed.
Embryo C shaped.
 By the time embryos tiny heart begin to
beat.
 Neural tube enlarges into 3 parts , soon to
become a very complex brain.

46. 6TH WEEK
 In this week growth is fast.
 36th-42nd day- Digital rays in the hand and
foot plate appear.
Brain vesicles prominent.
- External auricle , formed from auricular
hillock
- Umbilical herniation initiated.
 Eyes ears limbs toes become identifiable.

47. 7TH WEEK
 43rd-49th day – Pigmentation of retina
vissible
- Digitals separating.
- Nipples and eyes formed.
- Maxillary swelling fuse with
medial nasal swelling and upper lip is
formed.
- prominent umbilical herniation.
 Major muscle system is developed.
 The child has its own blood type from
mothers.

48. 8TH WEEK
 Limbs long and bend at elbows, knees,
fingers,toes free.
 Face more human like.
 Tail disppears.
 Umbilical herniation persist end of 3rd week.
 By eighth week all organs develop, and
embryo is now called foetus.
 Foetus is about half inch long.
 It is protected by amnionic sac, filled with fluid.