Summary on Fertilization to help students learn the basic

1. Human Fertilization
Presented by:
Lhaineihoi
khongsai
Phase 3 Part– I, 2022 Batch,
Anatomy Elective

2. CONTENT
•INTRODUCTION
•IMPORTANT EVENTS OF
FERTILIZATION
•PHASES OF FERTILIZATION
•SIGNIFICANCE
•COMPLICATION
•CLINICAL APPLICATIONS
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3. INTRODUCTION
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• FERTILIZATION :
• It is a process by which male and female gametes
fused.
• SITES OF FERTILIZATION :
 Occurs in ampullary region of uterine tube.
 Ampullary region is the widest part of fallopian
tube and is close to ovary.
• TYPES :
 External
fertilization
 Internal
fertilization

4. EXTERNAL
FERTILIZATIO
N
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 Occurs when both sperm and eggs are deposited
into the water.
 There is the addicted complication of addiction
that gametes of many species are mixed together.
 In external fertilization, a large number of both
gametes are available, although more sperm than eggs.
• Eg : Fishes ,
Amphibians

5. INTERNAL
FERTILIZATIO
N
 Occurs when the egg is retained in the body of a
female, and the sperm are deposited there by the male.
 In internal fertilisation, there are very often very
few eggs, but a large number of sperm.
• Eg : Humans, Dogs, and Cats.

6. IMPORTANT
EVENTS
• Transport of Oocyte(female gamete).
• Transport of sperm.
• Capacitation.
• Acrosome reaction.
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7. Transport of Oocyte(female gamete)
 Sweeping movements of fimbriae.
 Rhythmic muscular contractions of
the tube.
 Motion of cilia in the tubal mucosa.
 Fluid currents.
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8. Transport of sperm
 Human sperm are deposited into the
anterior vagina and they quickly
contact cervical mucus and enter the
cervix.
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9. Capacitation
 Functional maturation within the
female reproductive tract.
 Last for approximately 7 hours.
 Removes glycoprotein coat & seminal
proteins. Prepares sperm for acrosomal
reaction.
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10. Acrosome reaction
 The acrosome reaction is a crucial step
during gamete interaction in all species,
including man.
 It allows spermatozoa to penetrate the
zona pellucida and fuse with the
oocyte membrane.
 Spermatozoa unable to undergo the
acrosome reaction will not fertilise
intact oocytes. 10

11. Phases of Fertilization
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1) Phase 1 -Penetration of the corona
radiata.
2) Phase 2 -Penetration of the zona
pellucida.
3) Phase 3 -Fusion of the oocyte and sperm
cell.

12. Phase 1 -
Penetration of the
corona radiata
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 Out of 200–300 million sperm, only 300–
500 reach the site of fertilization.
 Only one sperm fertilizes the ovum.
 Other sperm assist in dispersing the corona
radiata cells.
 capacitated sperm can pass through this
layer.

13. Phase 2 –
Penetration of the
Zona Pellucida
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 Zona pellucida: glycoprotein shell maintaining
sperm binding and inducing acrosomal
reaction.
 Acrosomal enzymes (e.g., acrosin) digest the
zona.
 Sperm contacts oocyte membrane → cortical
granule release.
 Causes zona reaction, preventing polyspermy
(no other sperm can enter).

14. Phase 3 -Fusion of
the
oocyte and sperm
cell
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 Sperm binds and fuses with the oocyte membrane.
 The head and tail of the sperm enter the cytoplasm;
the membrane is left behind.
 After entry, three key events occur:
1) Cortical and zona reactions – prevent
polyspermy.
2) Completion of 2nd meiotic division – formation of
female pronucleus.
3) Metabolic activation – formation of male pronucleus
and start of zygote development.

15. ZYGOTE
• After entry, most of the sperm break
down, leaving the nucleus and
centriole.
• The nucleus decondenses and
the centriole initiates an
aster of
microtubules that contacts the
egg nucleus.
• Depending on the species, fusion may
occur immediately or may require the 15

16. IMPLANTATION
 In humans, implantation is the stage
of pregnancy at which the embryo
adheres to the wall of the
uterus.
 At this stage of prenatal
development, the conceptus is called
a blastocyst.
 It is by this adhesion that the embryo
receives oxygen and nutrients from the
mother to be able to grow.
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17. SIGNIFICANCE
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 Restores diploid number.
 Determines the sex of the embryo.
 Activates the ovum for development.

18. COMPLICATION OF
FERTILIZATION
• Polyspermy – multiple sperm entry; results in triploidy.
• Dispermy/Digyny – extra chromosome sets; abnormal
zygote.
• Parthenogenesis – development without fertilization
(rare).
• Ectopic fertilization – in fallopian tube; may cause
ectopic pregnancy.
• Molar pregnancy – trophoblastic
proliferation without embryo.

19. Clinical Applications
 Assisted Reproductive Techniques (ART):
 In Vitro Fertilization (IVF)
 Intracytoplasmic Sperm Injection (ICSI).
 Gamete/ Zygote Intrafallopian Transfer
(GIFT/ZIFT).
 Contraceptive methods prevent fertilization:
Barrier, hormonal, surgical.

20. CONCLUSION
• Human fertilization is the union of an egg and
sperm ,usually occuring in the ampulla of
the fallopian t u b e .
• The r esult of t h i s union i s t he production
of a zygote cell , or f e r t i l i zed egg ,
initiating
prenatal development.
• The process of fertilization involves a sperm
fusing with an ovum.
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21. REFERENCES
 Langman’s Medical Embryology – T.W. Sadler.
 Inderbir Singh’s Human Embryology.
 Moore & Persaud: The Developing Human.
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22. THANK
YOU