The topic discussed here is the Process of fertilization, different stages of fertilization, Implantation, Gastrulation, Formation of foetal membranes, Development of Embryo, Labor & Parturition

1. HUMAN
REPRODUCTION
FERTILIZATION & EMBRYO DEVELOPMENT

2. INTRODUCTION

3. FERTILIZATION
Fertilization (also called syngamy) involves
the fusion of haploid male and female gametes
to form diploid zygote.
Fertilization in human beings is internal and
takes place in the proximal part of fallopian
tube of the female.
Fertilization results in the formation of zygote
which then develops to form the embryo.

4. STAGES OF FERTILIZATION

5. Stages of Fertilization
Sperms are deposited in the
vagina and moves to the
oviduct.
1. Large number of sperms reach and
surround the ovum.
2. One of the sperms manages to
penetrate the egg membrane and
enter inside.
3. The sperm and egg nucleus fuses completing fertilization.

6. FERTILIZATION
• Fertilization involves the following processes
A. Approach of sperm to ovum
B. Penetration of Sperm
C. Cortical reaction
D. Fusion of gametic nuclei

7. APPROACH OF SPERM TO OVUM
• Seminal fluid contains as many as 200-300 million sperms.
• Many die due to acidity of female genital tract and many sperms are engulfed
by the phagocytes of the vaginal epithelium and only 100 sperms reach the
fallopian tube.
• The physiological maturation of sperms called Capacitation occurs inside
the female genital tract in the presence of viscous fluid secreted by the
epithelial lining of oviducal mucosa.

8. Fertilizin-Antifertilizin reaction
• The ovum secretes a chemical
substance called Fertilizin, which has
number of spermophillic sites on its
surface where the sperms of specific
species can be bound by their
antifertilizin reaction.
• This is to reduce the number of
sperms that fuse with the ovum and
reduce the change of polyspermy.

9. PENETRATION OF THE SPERM
• The acrosome releases sperm lysins
which dissolve the egg envelopes.
• Sperm lysin contain hyaluronidase
which dissolves hyaluronic acid in the
intercellular spaces of corona radiata.
• Corona-penetrating enzyme (that
dissolves the corona radiata)
• Acrosin (dissolves the zona
pellucida).
• Only the sperm nucleus and middle
piece enter the ovum.

10. CORTICAL REACTION

11. FUSION OF GAMETIC NUCLEI
• The entry of sperm stimulates the
secondary oocyte to undergo
meiotic-II division which produces
the ovum and second polar body.
• The centrioles of middle piece of
sperm form a spindle.
• The nuclear membrane degenerate
and the chromosome lie on two
poles, but later mix up and this
process is called Amphimixis.

12. SIGNIFICANCE OF FERTILIZATION
• It stimulates the secondary oocyte to undergo second maturation division to
release second polar body and to form haploid ovum.
• It restores the diploidy (2N = 46 in human beings ) in the zygote.
• It combines the characters of two parents and introduces variations and
helps in evolution.
• Sex chromosome of the sperm is either X or Y which helps in sex
determination. Fusion of X-chromosome containing sperm with X-
chromosome contain ovum results in a female baby
• While Y-chromosome containing sperm fuses with X-chromosome
containing ovum and results in a male baby.

13. MONOTREME MARSUPIALS PLACENTAL

14. BLASTOCYST FORMATION

15. FORMATION OF BLASTOCYST
(CLEAVAGE)
• The rapid mitotic division of zygote to form a hollow, spherical, multicellular
developmental stage called blastula, also called as Blastulation.
• Cleavage begins in the fallopian tube during the conduction of zygote towards
uterus.
• Cleavage causes the formation of two cell stage and the cleavage is repeated till a
32-cell stage is achieved. This is called the Morula stage.
• The cells that are formed due to cleavage are called as Blastomeres. Morula
consists of two different types of blastomeres
• Micromeres : The peripheral transparent cells
• Macromeres : The central and larger cells.

17. BLASTOCYST
The blastomeres in the Morula stage gets rearranged to form Blastocyst.
The outer layer of cells becomes flat and form Trophoblast or
Trophoectoderm, which draws the nutritive material secreted by the
uterine endometrial glands.
The fluid absorbed by trophoblast collects in the new central cavity called
Blastocoel or segmentation cavity.
As the amount of nutritive fluid increases in blastocoel, morula enlarges
and takes the form of a CYST and is now called Blastocyst or
Blastodermic vesicle.
The cells of trophoblast do not participate in the formation of Embryo
proper, they form the protective and nutritive extra-embryonic membranes
such as Chorion for placenta formation, Amnion for protection from
injury and dessication.

18. STAGES AFTER FERTILIZATION
Morula
Blastula
Day 7 to 9
MORULA: A solid round ball of 16 cells
BLASTULA: A
hollow round
ball with a cavity
in the center

19. IMPLANTATION

20. IMPLANTATION& PREGNANCY
Process of attachment of the
blastocyst on the wall of the
uterus is called implantation.
It occurs between7th to 9th day
after fertilization.
PREGNANCY/ GESTATION: The period of
development of an offspring in the
uterus from conception until birth.
Successful
implantation leads
to pregnancy

23. GASTRULATION

24. FORMATION OF ENDODERM &
EMBRYONIC DISC

25. FORMATION OF MESODERM

26. EXTRA EMBRYONIC MEMBRANES

27. PLACENTATION

28. Placentaand Umbilicalcord
PLACENTA: Temporary endocrine tissue that provides protection and
nourishment to the developing embryo.
UMBILICAL
CORD: A
tubular
connection
between the
developing
embryo and
the placenta
of the
mother
PLACENTA
FUNCTIONS-
Passing of O2 and
nutrients to the fetus
from mother
Passing of CO2 and
waste products from
fetus to mother
Secretes hormones
progesterone and
estrogen

29. ORGANIZATION OF MATURE PLACENTA

30. DEVELOPMENT OF EMBRYO

31. Development offoetus
The membranes
associated with the
embryo and that
surround and protect it
are called as the foetal
membranes.

32. Foetal membranes CHORION: Outermost foetal
membrane enclosing the embryo. It
contributes to development of
placenta
AMNION: Innermost
foetal membrane. It forms
the amniotic sac
Allantois – is a foetal membrane
that develops from the
alimentary canal and important in
forming umbilical cord

33. Amniotic fluid
Function:
• Acts as cushion for the embryo, protecting it from shocks and jerks.
• It prevents sticking of foetus to the amnion.
The fluid present
inside the amniotic
sac is called
amniotic fluid.

34. Embryo and foetus
Embryo –
1. The development stage of
baby till first 8 weeks
2. Does not resemble the parent
Foetus–
1. The development stages of
baby at 12 weeks
2. Resembles the parent

35. Comparison of Embryo developmental stages

36. THE FOETUS Placenta
Umbilical cord
Foetus
Amniotic sac
Amniotic fluid
Uterus
Cervix
Vagina

37. LABOR

38. http://lgfl.skoool.co.uk/content/keystage3/biology/pc/learningsteps/HUFLC/launch.html
1. Foetus turns upside down
2. Head is placed above the cervix
3. Foetus releases hormones
4. Pressure in the uterus stimulates release
of oxytocin
5. Oxytocin stimulates the contraction
of the muscle of the uterus
6. Mother feels small contractions of the
wall of uterus.
7. This is the beginning of LABOR
The forceful muscular contractions that lead to the
birth is called LABOR.
LABOR

39. LABOR & PARTURITION
The muscles of the uterus starts to contract strongly.
This pushes the baby to the cervix.
The cervix dilates and the baby’s head is pushed through the vagina.
The pressure breaks the amniotic sac, releasing amniotic fluid.
Parturition: The act of expelling the foetus after a complete term of
pregnancy or gestation.

40. LABOR & BIRTH
• Oxytocin- causes contractions
• Relaxin- relaxes the cervix and pelvic
ligaments for easy birth.

41. LACTATION

42. LACTATION
• During pregnancy the size of mammary glands increases.
• The release of stored milk after parturition is called lactation.
• Milk secretion begins usually within 24 hrs.
• The first fluid that is released after birth is called colostrum.
Oxytocin – milk letdown hormone
Prolactin- promotes lactation

43. MAMMARY GLANDS
• Modified milk producing sweat glands.
• Each breast contain 15-20 glandular
lobes separated from one another y
dense or fibrous connective tissue and
adipose tissue.
• Each lobe is made up of a number of
lobules having glandular or secretory
tubuloalveoli.
• The cells of alveoli produce milk

44. MAMMARY GLANDS
• The alveoli open into mammary
tubules and the mammary tubules
into mammary ducts.
• Mammary ducts form a broad
Mammary Ampulla (lactiferous sinus)
for storing milk.
• A lactiferous duct develops from
Mammary Ampulla, each glandular
lobe produces a separate lactiferous
duct that open at the nipple by
separate pores.

45. TWINS

46. Twins
Off-springs produced in the same pregnancy.
They may be-
• Monozygotic or identical twins- arise
from single egg fertilsed by a single sperm.
• Dizygotic or fraternal twins- two eggs
fertilized by two different sperms.

47. Twins
Identical
• Single fertilised egg gets
split into two and both
develop as different
individuals.
• They may share a common
placenta and amnion.
• Both the children are of the
same sex.
Non-identical
• Two eggs released from the
ovaries are fertilised at the
same time both form separate
individuals.
• Each has two separate
placenta and amnion.
• The children may or may not
be of the same sex.

48. Siamesetwins or conjoint twins

49. In-vitro fertilisation

50. THANK YOU