1. JOURNEY OF AN
EMBRYO

2. SPERMATOGENESIS
• A process where male spermatogonia develop
into mature spermatozoa.
• Occur in testes and epididymis in mammals
and takes approximately 64 days.

4. • Step 1 – Spermatocytosis
• Step 2 – Meiosis in Sertoli cells
• Step 3 – Spermiogenesis
STEP IN SPREMATOGENESIS

5. • Monospermy – fusion of a single sperm and
egg nuclei
• Polyspermy – excess of adhesion sites that
leads to fusion of a single engg with more
than 1 sperms.
MONOSPERMY & POLYSPERMY

6. OOGENESIS

9. FERTILIZATION

10. EVENTS THAT LEADS TO
FERTILIZATION

13. General steps of early
embryonic development

14. Embryology
Morula, 8 cell stage
1 - morula, 2 - blastula
1 - blastula, 2 - gastrula with blastopore;
orange - ectoderm, red - endoderm.

15. There are 4 stages of embryonic
development:
Cleavage
Patterning
Differentiation
Growth

16. CLEAVAGE PRODUCES A BALL OF
CELLS FROM ZYGOTE

17. • cleavage is the division of cells in the early
embryo
• The zygotes of many species undergo rapid
cell cycles with no significant growth,
producing a cluster of cells the same size as
the original zygote.
MEANING

18. PATTERN OF CLEAVAGE
1. Amount and distribution of yolks in their eggs
• Isolechital
• Mesolechital
• Telolechital
• Centrolechital
2. Polarity of eggs
• Animal pole
• Vegetal pole

19. Types of cleavage:

20. Cleavage patterns followed by holoblastic and
meroblastic eggs
Holoblastic Meroblastic
•Bilateral (tunicates,
amphibians)
Discoidal (fish, birds,reptile)
Radial (sea urchin, amphioxus) •Superficial (insects)
Rotational (mammals)
Spiral (annelids, mollusks)

21. Spiral cleavage

22. GASTRULATION

23. - a phase early in the development of most
animal embryo, during which the morphology
of the embryo is dramatically restructured by
cell migration.
GASTRULATION
- a phase early in the development of most
animal embryos, during which the
morphology of the embryo is dramatically
restructured by cell migration.

24. • The purpose of gastrulation is :
- to position the three embryonic germ layers,
the endoderm, ectoderm and mesoderm.
• gastrulation occurs after implantation,
around days 14-16 after fertilization in human
embryogenesis. (in human )

25. GATRULATION IN SEA URCHINS

26. GASTRULATION IN FISH

27. GASTRULATION IN BIRD

28. EVENTS IN DEVELOPMENT THAT
INVOLVED THE MIGRATION OF
CELLS WITHIN THE EMBRYO
DEVELOPMENT

29. About 1th week
•After fertilization,embryo reaches two-cell stage
•The blastula implants into the uterus
2th week
•Within 2 weeks,many thousand of cells formed(embryo)
About 5th
week
•A gestational sac on ultrasound
•Embryo at 4 weeks after fertilization.
6th
week
•In the beginning of the 6th
week,a small ring called yolk sac on
ultrasound
•At the end of the 6th
week the fetal pole and perhaps cardiac
activity in the embryo
Embryo at 4 weeks after
fertilization.

30. At 7th
week
A well defined fetal pole and deinite cardiac cavity
By 9th
week
A baby is called fetus. At this time the heartbeat with a doptone device about
50% of the time can heard
is about five weeks old (or from the
seventh week of menstrual age).
Fetus at 8 weeks
after fertilization.
Fetus at 8 weeks after fertilization.
This embryo is also from an ectopic
pregnancy, this one in the cornu (the part
of the uterus to which the Fallopian tube
is attached). The features are consistent
with a developmental age of seven
weeks (reckoned as the ninth week of
pregnancy

31. At end of first trimester(12th
week)
Placenta formed and supply the baby with oxygen from mother’s blood supply,and
ridding wastes tthrough mom’s blood system
At 13th
week
Baby growing very quickly
Week 16th
– 20th
Mother may feel a fluttering that is baby’s movement(quickening)
Fetus at 18 weeks after fertilization
20th
week
Baby is half-way fully formed
Baby is quite active and moving often
21th week
Baby’s eyes still closed,movement is stronger,skin is pink
As baby and uterus grow,they are displacing organs that reside normally in the lower
abdomen and pelvis
Fetus at 18 weeks after fertilization

32. By 24th
week
Uterus having intermitent contractions
Baby weights over one and one half pound
Baby is consider viable(half babies born is survive at this stage)
26th
to 28th
week
Lungs matured
Baby starting to store part in the subcutaneous layer of skin and hair growing
Baby eyes is open
32th to 33th week
Baby weight about 4 ½ pounds and about 16-17 inches along
About 34th
week
Baby lung start to work well
From 36th
week
Baby consider fully develop Fetus at 38 weeks after
fertilization

33. NEURULATION
AND
ORGANOGENESIS

35. PROCESS OF NEURULATION
Neurulation begins
with the formation
of a neural plate, a
thickening of the
ectoderm caused
when cuboidal
epithelial cells
become columnar.

36.  Changes in cell shape
and cell adhesion
cause the edges of the
plate fold and rise,
meeting in the midline
to form a neural tube.

37. The cells at the tips of
the neural folds come
to lie between the
neural tube and the
overlying epidermis.
These cells become the
neural crest cells.
Both epidermis and
neural plate are
capable of giving rise to
neural crest cells.

38. Organogeneis is the period of animal
development during which the embryo is
becoming a fully functional organism capable of
independent survivial.
Organogenesis is the process by which specific
organs and structures are formed, and involves
both cell movements and cell differentiation.
Organogenesis requires interactions between
different tissues. These are often reciprocal
interactions between epithelial sheets and
mesenchymal.

39. ORGAN PRODUCED BY THE 3 GERM LAYERS