Download Paraxial Mesoderm

Formation of the notochord
The notochord is a rod-shaped aggregate of cells located cranial to the primitive streak
of the embryo. It occupies the midline coelomic space between ectoderm and endoderm.
The notochord is important because it induces formation of the head, nervous system
development, and somite formation. It marks the future location of the vertebral column and
the base of the cranium. Its ultimate fate is to become the nucleus pulposus of intervertebral
discs.
The notochord develops from the primitive node located at the cranial end of the
primitive streak. From the node, mesoderm-forming cells proliferate and migrate forward into
the future head region where they become the rod shaped notochord.
Somites (Somites Formation)
Somites are bilaterally paired blocks of paraxial mesoderm that form along the head to
tail axis of the developing embryo in segmented animals. In vertebrates, somites give rise to
the vertebrae of the spine, (and part of the occipital bone), skeletal muscle, cartilage, tendons
and skin.
The somitomeres (somatomeres): are cells that are derived from the loose masses
of paraxial mesoderm that are found alongside the developing neural tube, they are
approximately 50 pairs of somitomeres in the human embryo, begin developing in the cranial
(head) region, continuing in a caudal (tail) direction until.
Paraxial Mesoderm: Also known as presomitic or somitic mesoderm is the area
of mesoderm in the embryo that flanks and forms simultaneously with the neural tube. The
cells of this region give rise to somites, blocks of tissue running along both sides of the neural
tube, which form muscle and the tissues of the back, including connective tissue and
the dermis.
The somites develop (split) to form:
Dermatome: The dermatome is the dorsal portion of the paraxial mesoderm somite which
gives rise to the skin (dermis).
Myotome: The myotome is that part of a somite that forms the muscles of the animal.
Sclerotome: The sclerotome forms the vertebrae and the rib cartilage and part of the occipital
bone.
Somites Develop As Follows:
— mesoderm accumulates on each side of the notochord; this medially positioned mesoderm
is designated paraxial mesoderm.
— progressing from rostral to caudal over time, transverse fissures divide the paraxial
mesoderm into blocks. Each block is called a Somite.
Intermediate Mesoderm: Also known as
Intermediate Mesenchyme is a type
of mesoderm that is located between the paraxial mesoderm and the lateral plate. It
develops into the part of the urogenital system (kidneys and gonads), as well as the
reproductive system.
Lateral plate mesoderm: Is a type of mesoderm that is found at the periphery of
the embryo. It will split into two layers, the somatic mesoderm and the splanchnic mesoderm
(the somato layer forms the future body wall And the splanchnic layer forms the circulatory
system).