1. Fertilisation
© 2016 Paul Billiet ODWS

2. William Harvey (1578-1657) Sceptical about spontaneous generation
Observed embryo development of: chicks in eggs deer in uterus
omne vivum ex ovo
Two parents must come together physically to ensure reproduction
Leewenhoek’s microscope (1677) showed he was on the right track.
© 2016 Paul Billiet ODWS

3. The spermatozoan Head 50µm Midpiece Acrosome Haploid Nucleus Flagellum
Gray’s Anatomy
Flagellum
Mitochondria
Acrosome
Midpiece
Head
Haploid
Nucleus
50µm
Sperms (photomicrograph)
Sperms (SEM)
© 2016 Paul Billiet ODWS

4. Preparing the sperm cells
Storage in the epididymis → Maturation
Ejaculation → Activation
Ascension to the ovary → Capacitation
Near the oocyte → Acrosome reaction.
© 2016 Paul Billiet ODWS

5. Maturation Storage in epididymis
DNA condenses further (sperm head smaller)
Cytoplasm reduced (slender sperms)
Motility achieved but switched off
Plasma membrane composition changes.
© 2016 Paul Billiet ODWS

6. Activation
During ejaculation 2-6 ml of secretions are added to the sperm
In a set sequence
Epididymis
Seminal vesicle – gelatinous, fructose rich, prostaglandins
Prostate - protease
Urethra – alkaline pH 7-8.
© 2016 Paul Billiet ODWS

7. Capacitation
The journey from the vagina to the end of the fallopian tube
The sperms become motile
The secretions of the cervix change at ovulation
They become sperm friendly
The sperm rest at staging posts en route (crypts)
The plasma membrane changes so the acrosome reaction is possible.
© 2016 Paul Billiet ODWS

8. Acrosome reaction The acrosome releases hydrolytic enzymes
Digest through the zona pellucida surrounding the oocyte.
© 2016 Paul Billiet ODWS

9. The oocyte
Human oocyte
100µm
Mouse oocyte
© 2016 Paul Billiet ODWS

10. Fertilisation sea urchin
Sperm acrosomes digest surrounding jelly
© 2016 Paul Billiet ODWS

11. Fertilisation Horse zygote Fertilisation (SEM)
© 2016 Paul Billiet ODWS

12. Fertilisation
Tip of acrosome process attaches to sperm cell receptor site
© 2016 Paul Billiet ODWS

13. Fertilisation
Vitelline layer lifts
© 2016 Paul Billiet ODWS

14. Fertilisation Microvilli form to wrap around sperm head
© 2016 Paul Billiet ODWS

15. Fertilisation
Sperm head drawn into oocyte
© 2016 Paul Billiet ODWS

16. Fertilisation
© 2016 Paul Billiet ODWS

17. Fertilisation
Cortical granules (vesicles) fuse with oocyte plasma membrane
Cortical reaction lifts away vitelline layer
Enzymes change the receptor site proteins
Other sperms excluded
© 2016 Paul Billiet ODWS

18. Cortical reaction Reaction spreads across the oocyte surface in 20s
Fertilization the calcium wave
© 2016 Paul Billiet ODWS

19. Fertilisation Sperm head drawn in Membrane disintegrates
Sperm mitochondria digested
© 2016 Paul Billiet ODWS

20. Fertilisation Vitelline layer becomes fertilisation membrane
Chemically transformed by the enzymes released
© 2016 Paul Billiet ODWS

21. Ovulation to implantation
morula
blastocyst
zygote
ovulation
fertilisation
implantation
© 2016 Paul Billiet ODWS