Detail process of human fertilization

1. Fertilization Process
in Mammals (Human)
Mr. R. K. Lodha

2. Anatomy of Sperm

3. Anatomy of Ova

5. MATURE (GRAAFIAN) FOLLICLE

6. Ovum and sperms: (In vitro)
The surfaces of unfertilized eggs are usually smooth in appearance. The mottled look
of this egg is not normally seen, but apparently all the ova from this woman had this
appearance.
From this photograph, it
should be clear that the
heads of human sperm
are less than 1/20 the
diameter of human eggs.
sperm heads

8.  The usual site of fertilization is the ampulla of the uterine tube,
its longest and widest part.
⚫ Spermatozoa may remain viable in the female reproductive tract
for several days.
 If the oocyte is not fertilized here, it slowly passes along the
tube to the uterus, where it degenerates and is resorbed.
 Although fertilization may occur in other parts of the tube, it does
not occurin the uterus.
 Chemical signals (attractants), secreted by the oocyte and
surrounding follicular cells, guide the capacitated sperms
(sperm chemotaxis) to the oocyte.
Site of fertilization

10. Morphology of the Oviduct:
Fallopian tube
H & E × 150
S = smooth muscle
E = ciliated epithelium Fallopian tube
Azan × 320
From Wheater’s Functional Histology, 4th ed., 2000.

11. Pre- fertilization events
 Helping the sperm:
At ovulation, the cervical mucus increases in amount
and becomes less thick, allowing easier sperm
transport.
Passage of the sperm through the uterus and oviduct
occurs mainly due to muscular contractions of these
organs.
 Oocyte:
The ends of the oviducts come into close contact
with the ovary during ovulation.
Fimbriae of oviduct ends “sweep” the ovulated ovum
into the oviduct.
Peristaltic waves of oviduct musculature bring the
ovum into the ampulla of the oviduct.

12. Pre- fertilization events

13. Fertilization facts:
 Completed within 24 hours of ovulation
 Approximately 400 to 600 MILLION sperms are
deposited at cervical opening during ejaculation.
Some sperm are held up by the folds of the cervix and
are gradually released into the cervical canal; this gradual
release increases the chances of fertilization.
Most human sperms do not survive longer than 48 hours
in the female genital tract.
 Only about 200 sperms reach the fertilization site;
most degenerate and are absorbed by the female
genital tract.

14. Mechanism - We can understand the process
of fertilization in following steps.
1. Movement of sperms towards ovum.
2. Entrance of sperms in the ovum.
3. Activation of ovum.
Approach of sperm towards the egg
It is a chance factor, so sperms perform random
(directionless) movement. To increase the chances
of approach of sperm towards egg there are mainly
two adaptation
(a)Number of sperms is very high :- e.g. In man
20 to 120 million sperms are present per cubic mm
of semen.
(b) Egg is 1000 times larger than sperm
- Some special proteins are found on the surface
of egg and sperm to help in fertilization.
Fertilization events

16. Process of Fertilization
Acrosomal reaction and penetration
Activation of ovum
Amphimixis
Capacitation and contact
Approach of sperm to ova

17. found on the surface of
According to
"fertilizins" are
Fertilizins are glycoproteins or
Lillie, chemicals named as
egg.
acid
mucopolysaccharides.
According to Ballinsky, an acidic protein named
as Antifertilizin is present on the surface of
sperms. "Fertilin" proteins are also present on
sperm surface.
Both the proteins are specific for a
particular species. Antifertilizin present on sperm
of a particular species will react with fertilizin
present on egg of the same species of animals.
Chemotaxis

18. Capacitation: readying the sperm
 Sperms cannot fertilize oocytes when they
are newly ejaculated.
 This step is a biochemical event.
 The process of capacitation takes 5-7 hours.
 Capacitated sperms are more active.
 Location: capacitation occurs in the uterus
and oviducts and is facilitated by substances of
the female genital tract.
 The acrosomal reaction cannot occur until
capacitation has occurred.

19.  Conditioning occurs in the uterine tube, having
interaction between the sperm and mucosal
surface of the tube
 During this, a glycoprotein coat and seminal proteins
are removed from the acrosomal region by secretion
of uterine glands.
 Thereby completing the capacitation and permitting
acrosomal reaction to occur.
Ejaculated sperm Maternal factors Capacitated sperm
Capacitation: readying the sperm

22. - According to Washerman and Sailing
(1989) a specific pair of protein
molecules is found on the surface of
mammalian sperm, which can recognise
specific carbohydrates and proteins in
ZP3 region of zona pellucida. The bindin
protein of sperm reacts with these
molecules to initiate the changes in
acrosome. A specific sugar galactose
remains attached with ZP3 glycoprotein.
The sperm fails to recognise the ovum of
its own species, if this sugar is removed
from zona pellucida.
- In addition to these
glycoproteins, there are some hormones
also, which help in fertilization.
Recognition

23. • The hormones present at the surface of sperm are
called androgamones. These are of two types.
Androgamone first & androgamone second.
• Androgamones I help in the energy conservation
of sperms.
• Androgamones II dissolve the gelatinous covering
present all over the egg.
• Hormones present at the surface of egg are called
gyanogamones these are of 2 types.
• (a) Gyanogamones I - this hormone neutralizes
Androgamone I and activates sperm to move
• (b) Gyanogamones II - It makes sperm head
sticky.
Role of Hormone

24. • The acrosomal reaction is triggered when the
sperm meets the egg
• The acrosome at the tip of the sperm releases
hydrolytic enzymes that digest material
surrounding the egg
• In mammals, zona pellucida ZP-3
glycoprotein which triggers Acrosomal
reaction.
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
The Acrosomal Reaction

25. BARRIERS PROTECTING
THE FEMALE GAMETE
1. Corona Radiata cells
2. Zona Pellucida
covering
3. Vitelline membrane
of secondary
oocyte Vijaylaxmi Pattanshetti
Vitelline membrane

26. Fig. 47-3-1
Basal body
(centriole)
Sperm
head
Sperm-binding
receptors
Acrosome
Jelly coat Vitelline layer
Egg plasma
membrane

27. Fig. 47-3-2
Basal body
(centriole)
Sperm
head
Sperm-binding
receptors
Acrosome
Jelly coat
Egg plasma
membrane
Hydrolytic enzymes
Vitelline layer

28. Fig. 47-3-3
Basal body
(centriole)
Sperm
head
Sperm-binding
receptors
Acrosome
Jelly coat
Egg plasma
membrane
Hydrolytic enzymes
Vitelline layer
Acrosomal
process
Actin
filament
Sperm
nucleus

29. Fig. 47-3-4
Basal body
(centriole)
Sperm
head
Sperm-binding
receptors
Acrosome
Jelly coat
Egg plasma
membrane
Actin
filament
Sperm plasma
membrane
Sperm
nucleus
Acrosomal
process
Fused
plasma
membranes
Hydrolytic enzymes
Vitelline layer

30. Fig. 47-3-5
Basal body
(centriole)
Sperm
head
Sperm-binding
receptors
Acrosome
Jelly coat
Egg plasma
membrane
Acrosomal
process
Actin
filament
Sperm
nucleus
Sperm plasma
membrane
Fused
plasma
membranes
Hydrolytic enzymes
Vitelline layer
Fertilization
envelope
Cortical
granule
Perivitelline
space
EGG CYTOPLASM

31. • Enzyme of acrosome (Hyaluronidase and sperm lysins) dissolve the egg membrane. This is called acrosomal reaction.
• As the result sperm head make the contact with the plasma membrane of egg, now inner membrane of acrosome evaginates
outside and form rigid tube is called acrosomal filament.
• Acrosomal filament provide stimulus to plasma membrane of egg and due to stimulus of sperm, egg is induce for fertlization.
• Mammalian sperms do not form this type of filament becouse mammalian sperms are highly active and provide stimulus to
plasma-membrane of egg without any filament. Mammalian sperms acquire activity at two places. First-epididymis and second-
vagina. Vaginal secretion make the sperm highly active and sperm acquire capacity of fertilization is called capacitation.
BICHEP.COM

32. Binding of sperm to extra cellular
envelopes
 Passage of sperm through the corona radiata depends
on enzyme action:
 Flagella action also aids corona radiata penetration.
 Penetration of the zona pellucida around the oocyte:
 Once sperm penetrates zona pellucida, the zona
reaction occurs:
This reaction makes the zona pellucida impermeable to
other sperms.
When more than one sperm manages to enter the ovum
(dispermy = 2; triploidy = 3), the fetus nearly always

33. Passage through extra cellular
envelopes
• Head and tail of a sperm enter the cytoplasm of the
oocyte, but the sperm plasma membrane remains
behind.
The secondary oocyte was previously
arrested in metaphase of the 2nd meiotic
division, and now forms the mature ovum and

34. Response of egg:
(1) Due to stimulus of sperm, meiosis-II is induced in human egg by excluding second polar body becoming
mature ovum

35. Fusion of sperm and egg
pronuclei
 Formation of male and female pronuclei:
Chromosomal material of the sperm
decondensates and enlarges
Chromosomal material of the ovum
decondensates following the completion of
meiosis
 At this stage, the male and female
pronuclei are indistinguishable.
 As they grow, the pronuclei replicate their
DNA  still 1N (haploid)- 23
chromosomes, each in chromatid pairs

36. ▣ The male nucleus enters the egg cytoplasm and becomes
the male pronucleus.
▣ As a result of the sperm fusing with the egg plasma
lemma, the oocyte nucleus, which is at metaphase of the
second meiotic division, completes that division giving
rise to another polar body.
▣ Following the second meiotic division, what is now the
nucleus of the ovum becomes the female pronucleus.
▣ The haploid male and female pronuclei move toward one
another, meet, and fuse to form the diploid nucleus of the
zygote.
▣ The zygote will now proceed to undergo cleavage.

37.  The male and female
pronuclei are
indistinguishable from one
another.
 The second polar body can
be seen (arrow).
 The plasma membranes of
the two pronuclei are
dissolving and one diploid
nucleus will remain.
Fusion of the pronuclei

38.  Membranes of the pronuclei break down,
chromosomes condense and arrange
themselves for mitotic cell division
 On membrane dissolution, there is 1 cell
with 46 chromosomes = diploid (2N)
 The first cleavage follows shortly,
leaving 2 cells, each with 46
chromosomes.
 Mitosis in the new zygote uses
centrioles derived from the sperm.
 The oocyte has no centrioles.

39. • The sharp rise in Ca2+in the egg’s cytosol
increases the rates of cellular respiration and
protein synthesis by the egg cell
• With these rapid changes in metabolism, the
egg is said to be activated
• The sperm nucleus merges with the egg
nucleus and cell division begins
Activation of egg

40. Activation of egg : Due to stimulus of
sperm an enzyme is induced in
plasma-membrane of egg it is called
adenyl cyclase enzyme and function of
this enzyme is to catalyze c-amp in
egg cytoplasm.
c-AMP is the second messanger.
Cyclic AMP receives stimulus from
plasma membrane of egg and
transfers it in egg cytoplasm and
induces all the response of egg for
sperm.
All the response of egg for
sperm are collectively called
gyanogenesis.
.
Activation of egg

41. Due to stimulus of sperm, permeability of plasma
menbrane of egg increases specially for k+ and
Ca2+ ions. Function of Ca2+ ions is to inactivate
the cytostatic factors in egg. as a result egg is
now ready for cleavage (In egg cytoplasm
special type of protein called cytostatic factor are
present these factors prevent the cleavage in
unfertilized egg)
Due to stimulus of sperm, H+–Na+
pump activates and induces the plasma-
membrane of egg.
Function of this pump is to continuously influx H+
ions and outflux Na+ions. As a result
concentration of H+ion increases in egg
cytoplasm and develops an acidic medium. In
acidic medium, proteolytic enzyme become
active and liberate the m-RNA from
informosome. These m-RNA become active and
rapidly synthesize different types of protein and
enzymes . Due to more availability of protein and
enzymes metabolic activity of egg increases.

42. • (2) At the point of contact with sperm and plasma-
membrane of egg a cone-like structure is formed
called reception cone.
• After some time reception cone sinks in egg
cytoplasm along with sperm (entry of sperm is a type
of phagocytosis).
• With the entry of sperm all the cortical granules burst
and secrete a membrane around the egg is called
fertilization membrane (cortical reaction).
• It is secreted on inner surface of primary egg
membrane and perivitelline space become more
wide and amount of perivitelline fluid is also
increase.
• Function of perivitelline fluid and fertilization
membrane is to prevent the entry of sperm in egg.
• So normally only one sperm enter inside the egg
(monospermy).
• Sometimes more than one sperm enter inside
the egg (polyspermy).

43. • Amphimixis was discovered by O.Hertwig in the eggs of
sea - urchin.
Amphimixis

44. Two types of polyspermy are found in nature.
(1) Pathological polyspermy: In it the nuclei of all
the sperms fuse with egg nucleus. In such type
of condition embryo development does not
occur. (Due to polyploidy condition)
(2)Physiological polyspermy : In physiological
polyspermy nucleus of only one sperm fuses with
egg nucleus and rest of the sperm die in egg
cytoplasm. Dead sperm are called merocytes. In
physiological polyspermy normal embryo
development occurs.
Polyspermy is absent in human beings.
Polyspermy mostly occurs in megalecithal eggs.
Fertilization membrane and cortical granules are
absent in egg of rat & guinea pig.
Polyspermy

45. Prevention of polyspermy
 In mammals, prevention of polyspermy is
mainly achieved by:
 Changing of the electric potential of egg
membrane by pumping high amount of Na+
outside the egg surface-
 The cortical reaction occurs in fertilisation when a
sperm cell unites with the egg's plasma
membrane, (zona reaction).This reaction leads to
a modification of the zona pellucida that blocks
polyspermy-

46. Fast Block of polyspermy

47. Slow Block of polyspermy

48. The results of fertilization:
 Stimulates the secondary oocyte to complete
meiosis.
 Restores the normal diploid number of
chromosomes (46).
 Results in variation of human species as
maternal and paternal chromosomes
intermingle.
 The embryo contains only maternal
mitochondria because the sperm mitochondria
are dispersed into the egg cytoplasm and
discarded.
 Determines the sex of the embryo.

49. • In majority of animals, only head and
middle piece enter inside the egg and
tail is left outside.
• In mammals, whole sperm enters in the
egg.
• In some animals, only head of sperm
enters in the egg tail and middle piece
remain outside e.g. Hydra, Neries etc.
• After entering inside the egg, sperm
rotates by 1800. All the structures of
sperm dissolve in egg cytoplasm except
sperm nucleus and proximal centriole.
• The centriole of egg itself degenerates
at the time of second maturation
division.
• So proximal centriole of sperm starts
division, it divides into 2 daughter
centrioles, which migrate towards
opposite pole and start forming spindles. BICHEP.COM

50. Fate of sperm nucleus
The nucleus of sperm absorbs water from egg
cytoplasm and becomes enlarged. Now it is called
male pronucleus.
After meiosis - II egg nucleus occur in the form of
scattered vesicles then it is called as karyomeres
and after some time all the karyomeres assembled
to form complete nucleus is called female
pronucleus.
Male pronucleus and female pronucleus migrate
through definite routes and come close to each
other. These routes are called fertilization path.(It
has following parts)
BICHEP.COM

51. (1)Sperm penetration path - Male pronucleus for
some distance, moves at the equator of egg.This is
called sperm penetration path.
(2)Sperm copulation path :- Male pronucleus starts
migrating towards female pronucleus.
(3)Egg copulation path :- Female pronucleus
migrates towards male pronucleus. Both the
pronuclei come close to each other.
(4)Cleavage path - Both the pronuclei move together
to their final position which is somewhere in animal
pole.
At this final position nuclear membrane of both the
pronuclei degenerate and chromosomes of male and
female pronuclei form pairs. The mixture of male and
female chromosomes is called amphimixis.

53. 1.Oocyte completes its second maturation division on coming in
contact with the sperm.
2.Amphimixis process leads to the formation of a diploid zygote to
restore the normal diploid number of the chromosomes.
3.The centriole of sperm after entering into egg induces the egg to
undergo cleavage.
4.The paternal and maternal characters are transmitted to the
offsprings through the process of fertilization.
5.The peripheral changes occurring in the egg prevent the further
entry of sperm into the ovum, thus checking polyspermy.

54.  https://www.google.com/search?q=steps+of+fertilizatio
n+in+humans+animated+video&biw=1280&bih=610&sx
srf=ALeKk03qEMyuIAkWMst9o7_Ok_djn5YRjg%3A1621
592947011&ei=c4unYPwLqOHPuw_4lJWIAQ&oq=Steps
+of+fertilization+in+humans+ani&gs_lcp=Cgdnd3Mtd2l
6EAEYATIICCEQFhAdEB4yCAghEBYQHRAeOgcIABBHELA
DOgQIIxAnOgIIADoGCAAQFhAeUNgLWJkeYOg7aABwA3
gAgAHXAYgB7geSAQUwLjMuMpgBAKABAaoBB2d3cy13
aXrIAQjAAQE&sclient=gws-
wiz#kpvalbx=_e4unYKGqNNTfz7sP95mY4As17
 https://www.britannica.com/video/192622/Human-
embryonic-development-birth-fertilization
Video of fertilization: