Intra-Embryonic Mesoderm (General Embryology)

Intra-Embryonic Mesoderm

1. Formation of
Notochord
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2. Amniotic
cavity
Epiblast
1-Prenotochordal
process
Primitive
pit
Secondary
yolk sac
Endoderm
Bucco-pharyngeal
membrane LS
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3. Notochordal
process
Extension of primitive
pit into prenotochordal
process
Primitive streak
Connecting
stalk
Allantois
LS
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4. 2-Notochordal
canal
Cloacal membrane
Allantois
LS
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5. Notochordal
canal
Intraembryonic
mesoderm
TS
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6. Amniotic cavity
Yolk sac
Degenerating endoderm and floor of notochordal canal
Roof of notochordal canal
LS
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7. 3-Neurenteric canal
Buccopharyngeal
membrane
Cloacal
membrane
LS
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8. 4-Notochordal
plate
Notochordal plate (roof of the
canal) which intercalate (fuse) to
endodermal layer.TS
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9. TS Dr. SherifFahmy

10. 5-Definitive Notochord
TS Dr. SherifFahmy

11. Intra-embryonic Mesoderm
•It is formed from proliferating cells from sides
of primitive node and streak.
•It fills the space between ectoderm and
endodermexcept at buccopharyngeal
membrane, cloacal membrane (fusion
between ectoderm and endoderm caudal to
primitive streak) and median region which is
occupied by notochord.
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12. Primitive streak
Primitive
node and pit
ectoderm
Endoderm
Intra-embryonic
mesoderm
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13. Amniotic cavity
Amnio-
ectodermal
junction
Intra-emryonic
mesoderm
Secondary
yolk sac
Endoderm
Ectoderm
Bucco-
pharyngeal
membrane
Cloacal
membrane
Primitive streak
Primitive
node
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14. 17 th Day
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15. Differentiation of Intra-embryonic
Mesoderm
•Intra-embryonic mesoderm on each side
of notochord, divides into:
1-Paraxial Mesoderm:on both sides of
notochord.
2-Intermediate Mesoderm:Middle part of
the mesoderm.
3-Lateral plate Mesoderm:Lateral part
which communicates with that of the
opposite side infrontprochordalplate.
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16. Bucco-pharyngeal
membrane
Cloacal
membrane
Notochord
Intermediate mesoderme
Paraxial mesoderm
Lateral plate mesoderm
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17. 1-Paraxial Mesoderm
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18. Notochord
Paraxial mesoderm
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19. NotochordSomites of Paraxial
mesoderm
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20. 1-Paraxial Mesoderm
•It is the most medial mesoderm.
•It is divided into cubical masses called somites
(42 –44 pairs).
•Formation of somites starts At the 20th day
by formation of one pairat cranial region.
Then this followed by formation of 3 pairs/day
till day 30 then the rate becomes slower to
complete full number at the end 5
th
week.
•Somites are classified into: 4 occipital, 8
cervical,12thoracic,5lumbar,5sacraland8 –
10coccygeal.
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21. Dr. SherifFahmy

22. Dr. SherifFahmy

23. Dr. SherifFahmy

24. Fate (Organisation) of Somites
•1-Sclerotome:It is ventro-medial part
that form vertebral column and
intervertebral discs.
•2-Dermo-myotome:It is the dorso-
lateral part which subdivided into:
A-Dermatome:Forms dermis of skin.
B-Myotome:Forms skeletal muscles of
trunk and limbs.
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25. Notochord
Neural tube
Somite
Sclerotome
Myotome
Dermatome
Neural tube
Vertebra
Skeletal muscles
Dermis
Dermo-myotome
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26. Muscles of
back
Muscles of
anterolateral
aspect of body
Muscles of
limb
Dorsal ramus
of spinal nerve
Ventral ramus
of spinal nerve
Dermo-myotomes
of upper limb
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27. 2-Intermediate Mesoderm
•Narrow strip between paraxial
and lateral plate mesoderm.
•It is divided into many
segments.
•It forms uro-genital system.
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28. Lateral Plate Mesoderm
•Flat plate of mesoderm between intermediate
mesoderm and margin of embryonic disc.
•It is continuous with that of other side infront
prochordal plate.
•Intra-embryonic coelom:It is formed from fused
small cavities. This coelom forms serous
membranes of the body (pericardium, pleura and
peritoneum).
•Lateral plate mesoderm is split by the coelom into:
-Somatic mesoderm & Splanchnic mesoderm.
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29. Bucco-pharyngeal
membrane
Cloacal
membrane
Notochord
Intermediate mesoderme
Paraxial mesoderm
Lateral plate mesoderm
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30. NotochordSomites of Paraxial
mesoderm
Intermediate mesoderm
Intraembryonic coelom
Pericardium
Pleura
Peritoneal
canal
Cardiogenic
area
Septum
transversum
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31. Neural groove
Amnion
Somatic
mesoderm
Intraembryonic
coelom
Notochord
Splanchnic mesoderm
Paraaxial
mesoderm
Intermediate
mesoderm
Lateral plate
mesoderm
T.S.
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32. Amnion
Somatic
mesoderm
Intraembryonic
coelom
Splanchnic mesoderm
Lateral plate
mesoderm
T.S.
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33. Dr. SherifFahmy

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