Intra-Embryonic Mesoderm (General Embryology)
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Transcript of Intra-Embryonic Mesoderm (General Embryology)
Formation of Notochord
Dr. Sherif Fahmy
Amniotic cavity
Epiblast
1-Prenotochordal
process
Primitive pit
Secondary yolk sac
EndodermBucco-pharyngeal membrane LS
Dr. Sherif Fahmy
Notochordal process
Extension of primitive pit into
prenotochordal process
Primitive streak
Connecting stalk
Allantois
LSDr. Sherif Fahmy
2-Notochordal
canal
Cloacal membrane
Allantois
LS
Dr. Sherif Fahmy
Notochordal canal
Intraembryonic mesoderm
TS
Dr. Sherif Fahmy
Amniotic cavity
Yolk sac
Degenerating endoderm and floor of notochordal canal
Roof of notochordal canal
LS
Dr. Sherif Fahmy
3-Neurenteric canal
Buccopharyngeal membrane
Cloacal membrane
LS
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4-Notochordal plate
Notochordal plate (roof of the canal) which intercalate (fuse) to endodermal layer.TS
Dr. Sherif Fahmy
TS Dr. Sherif Fahmy
5-Definitive Notochord
TS Dr. Sherif Fahmy
Intra-embryonic Mesoderm• It is formed from proliferating cells from sides
of primitive node and streak.• It fills the space between ectoderm and
endoderm except at buccopharyngeal membrane, cloacal membrane (fusion between ectoderm and endoderm caudal to primitive streak) and median region which is occupied by notochord.
Dr. Sherif Fahmy
Primitive streak
Primitive node and pit
ectoderm
EndodermIntra-embryonic mesoderm
Dr. Sherif Fahmy
Amniotic cavity
Amnio-ectodermal junction
Intra-emryonic mesoderm
Secondary yolk sac
Endoderm
Ectoderm
Bucco-pharyngeal membrane
Cloacal membrane
Primitive streak
Primitive node
Dr. Sherif Fahmy
17 th DayDr. Sherif Fahmy
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 infront prochordal plate.
Dr. Sherif Fahmy
Bucco-pharyngeal membrane
Cloacal membrane
Notochord
Intermediate mesoderme
Paraxial mesoderm
Lateral plate mesoderm
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1- Paraxial Mesoderm
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NotochordParaxial mesoderm
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NotochordSomites of Paraxial mesoderm
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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 pair at 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 5th week.
• Somites are classified into: 4 occipital, 8 cervical, 12 thoracic, 5 lumbar, 5 sacral and 8 – 10 coccygeal. Dr. Sherif Fahmy
Dr. Sherif Fahmy
Dr. Sherif Fahmy
Dr. Sherif Fahmy
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.Dr. Sherif Fahmy
Notochord
Neural tube
Somite
Sclerotome
Myotome
Dermatome
Neural tubeVertebra
Skeletal muscles
Dermis
Dermo-myotome Dr. Sherif Fahmy
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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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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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.
Dr. Sherif Fahmy
Bucco-pharyngeal membrane
Cloacal membrane
Notochord
Intermediate mesoderme
Paraxial mesoderm
Lateral plate mesodermDr. Sherif Fahmy
NotochordSomites of Paraxial mesoderm
Intermediate mesoderm
Intr
aem
bryo
nic
coel
omPericardium
Pleura
Peritoneal canal
Cardiogenic area
Septum transversum
Dr. Sherif Fahmy
Neural groove
Amnion
Somatic mesoderm
Intraembryonic coelom
Notochord
Splanchnic mesoderm
Paraaxial mesoderm
Intermediate mesoderm
Lateral plate mesoderm
T.S.
Dr. Sherif Fahmy
Amnion
Somatic mesoderm
Intraembryonic coelom Splanchnic
mesoderm
Lateral plate mesoderm
T.S.
Dr. Sherif Fahmy
Dr. Sherif Fahmy
Dr. Sherif Fahmy