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

Dr. Sherif Fahmy

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


Cloacal membrane

Notochord

Intermediate mesoderme

Paraxial mesoderm

Lateral plate mesoderm

Dr. Sherif Fahmy

1- Paraxial Mesoderm

Dr. Sherif Fahmy

NotochordParaxial mesoderm

Dr. Sherif Fahmy

NotochordSomites of Paraxial mesoderm

Dr. Sherif Fahmy

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

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

Dr. Sherif Fahmy

2-Intermediate Mesoderm• Narrow strip between paraxial

and lateral plate mesoderm.• It is divided into many

segments.• It forms uro-genital system.

Dr. Sherif Fahmy

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


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


T.S.

Dr. Sherif Fahmy

Amnion

Somatic mesoderm

Intraembryonic coelom Splanchnic

mesoderm


T.S.

Dr. Sherif Fahmy

Dr. Sherif Fahmy

intra-embryonic mesoderm (general embryology)

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