Animal Reproduction/Theriogenology https://www.youtube.com/channel/UCHzZhYqMy10vsVRZdddEkUg

1. Early Embryogenesis
THER 608
Prof. Dr. Nasim Ahmad
Chap. 13

2. Basic Terms
Syngamy: Fusion of male and female pronuclei
Zygote: After fusion of male and female
pronuclei single-celled embryo
Embryo: An organism in early stages of
development
Fetus: Potential offspring that is still in the
uterus and of recognizable size
Conceptus: Product of conception
1. Embryo during the early embryonic stage
2. Embryo & extra embryonic membranes
during preimplantation stage
3. Fetus and placenta, post-attachment
phase.

3. • Ootid: When male and female pronuclie
appear, largest single cell, having an
enormous volume of cytoplasmic volume
relative to nuclear volume
• Blastomere: After first cleavage two celled
embryo
• Cleavage: First mitotic division
• Totipotency: Ability of single cell
(Blastomere) to give rise to an individual;
valid till 8 cell stage
• Morula: When solid ball of cells is formed
and blastomeres cannot be counted

4. • Gap junction: Junctions between cells of inner
portion of morula; allow intercellular
communication and enable inner cell to remain
in a defined cluster
• Tight junction: Junctions between cells of outer
portion of morula; prevent the materials passing
between adjacent cells
• Blastocyst: Embryo consisting of an inner cell
mass, blastocoele and trophoblast
• Trophoblast: The cell layer covering the
blastocyst that will form chorion
• Blastocoele: Cavity in central portion of
blastocyst

5. MORULA
COMPACT 8 cell embryo
Compact Morula

7. PREATTACHMENT
DEVELOPMENT OF
THE EMBRYO

8. Transitionofamorulainto
earlyblastocyst

9. Na+
[Na+]
H2O
Zona Pellucida
Trophectoderm
Inner Cell Mass
Blastulation
Tight Junctions
Gap Junctions

11. ZONA HATCHING
(Release of the blastocyst)
1. Blastocyst continue to undergo mitosis
2. Fluid continues to fill the blastocoele
3. Increased pressure within the embryo
4. Proteolytic enzymes by trophoblastic cells
5. Pressure pulses (blastocyst contract and relax)
6. All factors cause the ZP to rupture.
BLASTOCYST ELONGATION
Occurs in Cows & Sheep, but not Horses

12. Preattachment embryo development

13. Species 2-cell 4-cell 8-cell Morula Blast. Hatching
Cow 24h 1.5d 3d 4-7d 7-12d 9-11d
Mare 24h 1.5d 3d 4-5d 6-8d 7-8d
Woman 24h 2d 3d 4d 5d 5-6d
Timing of pre-attachment
Embryogenesis relative to ovulation

14. Uterine Location of Elongating
Ruminant Blastocyst
Corpus
Luteum
Bovine and Ovine
Cows 13-16 days
Sheep 11-16 days

15. Gastrulation
Blastocoele
Cavity
Endoderm
Inner Cell Mass Trophectoderm
Formation of
Germ
Layers

16. Gastrulation
EndodermEndoderm
Yolk Sack

17. Gastrula
Ectoderm
Endoderm
Trophectoderm

18. Gastrula
Ectoderm Mesoderm
Yolk Sack
Endoderm Trophectoderm
(Chorion)
Extraembryonic
Coelom

19. Germ Layers
• Ectoderm
– CNS
– Sense organs
– Mammary
glands
– Sweat glands
– Skin
– Hair
– hooves
• Mesoderm
– Circulatory
– Skeletal
– Muscle
– Reproductive
tracts
– Kidneys
– Urinary ducts
 Endoderm
» Digestive
» Liver
» Lungs
» Pancreas
» Thyroid gland
» Other glands

20. Development of extraembryonic membranes

21. Placenta Formation
Yolk
Sack
Chorion
Embryonic
Ectoderm
Mesoderm
Trophectoderm
Amniotic Folds
Extraembryonic Ceolom
Endoderm

22. Extraembryonic Ceolom
Amniotic Fold
Amniotic Cavity
Yolk
Sack
Allantois
Chorion

23. Yolk
Sack
Extraembryonic Ceolom
Chorion
Amnion
Amnionic Cavity
Carnuncle
Allantois
Uterine
Lumen

24. Chorion
Allantochorion
(Chorioallantois)
Allantois Cavity
Cotyledon
Amniotic Cavity
Amnion
Yolk
Sack

25. Placental Membranes
• Yolk Sack
– In birds to nourish embryo
– In mammal atrophies but source of blood
cells and primordial germ cells
• Amnion
– Non-vascular, fluid filled
– Fluid produced by fetus
– Protective cushion
– Ruptures at birth (not breaking of water)

26. Placental Membranes (cont.)
• Allantois
– Blood vessels
– Fuses with chorion
• Allantochorion or chorioallantois
• Brings blood vessels to chorion
• Chorion
– Outermost membrane
– Attachment to mother