Download DEVELOPMENT OF MESODERM,

DEVELOPMENT OF MESODERM,
PARAXIAL MESODERM AND
SCLEROMYOTOME AND FORMATION OF CARTILAGES
LEARNING OBJECTIVES
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At the end of lecture students should be able to know,
What is gastrulation.
Development of mesoderm.
Somitogenesis.
Formation of cartilage.
GASTRULATION(
Week 3-8)
• Gastulation is the process
which establishes the
formation of three germ
layered embryo:
– Ectoderm
– Mesoderm
– Endoderm
• Formation of trilaminar
embryonic disc by day 21.
THE THREE GERM LAYERS
 The three germ layers are the derivatives of epiblast
 The three germ layers give rise to all the tissues and organs of the body.
DEVELOPMENT OF MESODERM
 Paraxial mesoderm
 Intermediate mesoderm
 Lateral mesoderm
PARAXIAL MESODERM
 Thick plate of mesoderm located on each side of midline
 Becomes organized into segments called somatomeres in cranio-caudal
sequence.
INTERMEDIATE MESODERM
 Longitudinal dorsal ridge of mesoderm located between paraxial and lateral
mesoderm
 This ridge forms the Urogenital ridge
 Urogenital ridge forms the future kidneys and gonads
LATERAL MESODERM
 Thin plate of mesoderm located along the lateral side of embryo.
 Large spaces develop in the lateral plate mesoderm and coalesce to form
intraembryonic coelom
 Intraembryonic coelom divides lateral mesoderm into:
 Intraembryonic somatic mesoderm
 Intraembryonic visceral mesoderm
SOMITOGENESIS
 Process of segmentation development of
 axial system vertebrae, muscles and
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innervations.
Somites form from paraxial mesoderm in
anterior-posterior gradient, begins at
neurulation.
Two parallel columns of mesodermal cells
form along the longitudinal axis, on each
side of the notochord and neural tube.
Transverse fissures form in the
columns forming somitomeres in cranio caudal direction.
SOMITOMERES
 Somitomere 1-7 do not form somites, but contribute mesoderm to
pharyngeal arches
 The remaining somitomeres condense in cranio-caudal sequence forming
41-42 pairs of somites.
SOMITES
 Somites differentialte into:
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Sclerotome
Forms cartilage and bone component of veebral column
Myotome
Forms epimeric and hypomeric muscles
Dermatome
Forms dermis and subcutaneous area of skin
SUMMARY OF MESODERMAL DEVELOPMENT
FORMATION OF CARTILAGE
 Cartilage is derived from mesenchyme
 Avascular mesenchyme contains stem cells embedded in a delicate collagen
matrix
CHONDROBLAST
 Mesenchyme cells begin to differentiate into protochondral cells
 Protochondral cells divide to produce chondroblasts
CARTILAGE DEVELOPMENT
 The center fills with chondroblasts as the top and bottom edges continue to
differentiate.
 Stem cells remain on the edges
 Chondroblasts remain in the center and produce cartilage matrix.
 Stem cells at the edges produce fibroblasts and make the fibrous
perichondrium
 Chondroblasts in the center continue to divide
THANK YOU