The document summarizes the processes of fertilization, gametogenesis, implantation, and early embryonic development. It begins by describing fertilization as the union of an egg and sperm in the fallopian tube, forming a zygote. It then discusses gametogenesis, the formation of male and female gametes, including oogenesis and spermatogenesis. The next stages covered are implantation of the blastocyst in the uterus and formation of the placenta and fetal membranes. The document concludes by outlining the differentiation of the inner cell mass into the three germ layers and the formation of the amniotic cavity and yolk sac in early embryonic development.

3. Fertilization is the union of egg &
sperm, usually occurring in the ampulla
of the fallopin tube . The result of this
union is the production of a zygote cell,
or fertilized egg.

4.  The process of formation & maturation of
male & female gametes is known as
gametogenesis.
 It consist of:
A) Oogenesis
B) Spermatogenesis

5. The process involved in the development of a
mature ovum is called oogenesis.
 The formation of an oocyte from oogonia takes
followed by meiotic division.
 It is divisible in to 3 phases.
1) Multiplication phase
2) Growth phase
3) Maturation phase

7.  Spermatogenesis is the development of
male sex cells called sperms in the male
gonad (testis)
 The entire process is divided in to 2
phase
1. Formation of Spermatid
( Spermatocytois)
2. spermiogenesis

9.  Transformation occurs in the
spermatid
 The large spherical nucleus
becomes smaller by losing water
usually changes its shape in to
elongated structure
• The golgi bodies condense in to
a cap called acrosome
• Nucleus & acrosome forms head
of the developing sperm
• Cytoplasm with mitochondria &
centrioles move towards down
form cylindrical middle piece
 Two centrioles of middle piece
develop axial filaments
single thread – form vibratile tail

10. It is the process of fusion of the spermatozoon
with the mature ovum.
Location:- Ampullary part of the fallopian tube.
Fertilization life span of
Ovum – 12-24 hrs
Sperm- 48-72hrs

12.  Capacitation:- it is the removal of glycoprotein
& seminal plasma proteins from plasma
membrane that overlies the acrosomal region of
spermatozoa
 Acrosome reaction: it is the process of the
release of enzymes from the acrosome on the
head of the sperm,this process causes the sperm
to penetrate the zona pellucida of the egg and
begin fertilization.

13. A. passage of sperm through
corona radiate (CR)
B. penetration of zona pellucicla
 Complete dissolution of corona
radiata & penetration of ZP
occurs by the chemical action of
the hyaluronidase released from
the acrosomal cap of the sperm.
 soon after sperm fusion
penetration of other sperm is
prevented by zona reaction
( Hardening) oolema block
C. Fusion of cell membranes of
oocytes & sperm
 Plasma membrane of Oocyte
and sperm fuse
 Head & tail of the sperm enter
the cytoplasm of oocytes
 plasma membranes of sperm is
left behind on Oocyte surface

14. D. Formation of female pronucleus
 Oocyte finishes second meiotic division after the entry of
sperm
 It results in formation of mature Oocyte & a second polar body
E. Formation of male pro- nucleus
 Head & tail of the spermatozoon enter the cytoplasm of the
Oocyte
 Tail of the sperm degenerates
 As pronucleus fuse in to a single diploid aggregation of
chromosomes it become zygote.
 Chromosomes in the zygote are arranged on a cleavage of
spindle for further normal mitotic division
 Zygote has 23 maternal 23 paternal chromosomes
• X-bearing sperm 46XX zygote –female
• Y-bearing sperm 46XYzygote –male

16. After the zygote formation
typical mitotic division of
nucleus occurs & produce two
blastomeres.
 Two cell stage is reached after
30 hrs. of fertilization
 The blastomeres continue to
divide by binary division through
4,8,16 cell stage
 At 16 cell stage cluster of cell is
formed called as morula
 After 3 days the morula reaches
the uterine cavity through
fallopian tube
 Transport is slow & is controlled
by muscular contraction &
movement of cilia.
 Central cell is known as inner
cell mass outer cell is called as
outer cell mass

17.  Blastocystic cavity ( fluid filled space)
appears inside the morula after 4th day of
fertilization
 fluid from the uterine cavity passes zone
pellucida to form the cavity
 Fluid increases separates blastomeres
in to 2 parts:-
a. Trophoblast
b. Embryo blast
 Due to blastocyst enlargement the zona
pellucida becomes stretched thinned &
gradually disappears
 Lysis of zona & excape of embryo is
called Zona hatching

18. It is defined as the attachment of the blastocyst to the
epithelial lining of the uterus
 Implantation occurs after 6-7 days of fertilization
 It occurs through following stages
1. Apposition
2. Adhesion
3. Penetration & Invasion

19.  It occurs through pinopod formation
 Pinopods are fingerlike projections from the endometrial cell
surface
 Pinopods absorb the endometrial fluid
ADHESION:-
 Adhesion occurs with the help of adhesion molecules integrin ,
selectin & cadherin
PENETRATION & INVASION
 Penetration & Invasion occurs through the stromal cells in
between the glands
 It is facilitated by the histolytic action of the blastocyst
 With increasing lysis of stromal cells the blastocyst is burrowed
more inside compact layer of the decidua
 Penetrate deeply & allow the mature blood to enter into the
lacunar system
 Through the maternal blood the zygote (embryo) receives the
nutrition

20.  The cells of the blastocyst
differentiate in to an outer
trophectoderm & an inner cell
mass
 Just before implantation the
trophectoderm further divide
in to
a) Inner mononuclear cell
layer (Cytotrophoblast)
b) Outer Multinucleated
syncytium ( Syncytio
trophoblast )

21. The cytotrophoblast cells that invade the
decidua are called as “ Interstitial Extravillous
cytotrophoblast”
Cytotrophoblast that lines the villous stems are
villous cytotrophoblast
Placenta and the fetal membranes are derived
from the trophoblast

22. Decidua is the endometrium of the
pregnant uterus
 Layers of well develop Decidua
• Basal layer
• Functional layer
• Compact layer
o Basal Layer:- ( Deciduabasalis )
 Layer lies immediately above the
myometrium
 It remains inchanges
 It regenerates new endometrium
during the puerperium

23. o Functional layer:- ( Decidua capsularis)
 This layer consist of tortuous glands which are rich in
secretions
 Stromal cell are enlarged & affords defense against excusive
invasion by the syncytiotrophoblast
o Compact layer:- ( Decidua vera or parietalis )
 It forms the surface of the decidua composed of closely
packed stromal cells
o Decidual reaction:- the increased structural & Secretory
activity of the endometrium that is brought about in response
to progesterone following implantation is known as decidual
reaction.

24.  Provides good nidus for the implantation of the
blastocyst
 Supplies nutrition to the early stage of growing
ovum
 Decidua basalis helps in the formation of basal
plate of the placenta

25. CHORION & CHORIONIC VILLI
 Chorion is the outermost layer of the fetal
membrane
 It consists of two embryonic layer
 Outer trophoblast
 Inner primitive mesenchyme

26.  At 3rd week the syncytiotrophoblast produces
irregular fingerlike projections called primary
stem villi
 Which is surrounded by lacunar space, later it form
in to intervillous space
 With the insinuation of the primary mesoderm
in to the central core of the villi structure the
secondary villi are formed on 16th day
 Later mesodermal cells differentiate in to blood
cells forms villous capillary system
 The vascularised villi are called tertiary villi
which is completed by 21 days

27. Chorion frondosum :-
 The villi overlying decidua basalis continue to grow and
expand, & are called as Chorion frondosum
 The area surrounding the villi are blood space
Nutritive villi :-
 maternal blood circulates slowly, enable the villi to absorb
food & oxygen & excrete waste, these villis are known as
Nutritive villi
Anchoring villi:-
 few villi are attached more deeply in to the decidua and are
called as Anchoring villi

28.  It forms with in the blastoyst
 Inner cell mass is a cellular mass on one side is hollow
interior of the round embryo, the outer layer is called
trophoblast
• The trophoblast placenta
• Inner cell mass fetus
 Layers of inner cell mass
A. The ectoderm
B. Mesoderm
C. Endoderm

29. It forms the central & peripheral nervous system
 Epidermis layer of skin
 Pituitary gland
 Salivary glands
 Mucosal lining of nasal cavity
 Roof of the mouth

30. This layer Forms the :-
 bones
 Cartilage muscles, CVS,
 Kidney, gonads, suprarenals
 Spleen, most of genital treat
 Mesothelial lining of pericardial, pleural &
 peritoneal cavity
ENDODERM
 Epithelial lining of the GI tract, liver, gall bladder,
pancreas, respiratory tract
 Mucous membrane of urinary bladder, urethra
greater vestibular glands

31.  These three layer together known as embryonic
plate
 there are two cavities present in the inner cell
mass
 Amniotic cavity
 Yolk Sac
AMNIOTIC CAVITY
 Cavity lies on the side of the ectoderm
 It is filled with fluid
 It gradually enlarges & folds around the
embryo to enclose it
 The Amnion forms from its lining

32.  Lies on the side of the endoderm
 Provides nourishment to the embryo
 A part of it contributes to the formation of primitive gut
 Remainder resembles a balloon floating in front of
embryo
 Viteline duct:- the narrow channel connecting the yolk
sac with the intestine. Also called as umbilical duct

34. By Yo Yo