How does the scleratome form?
Cells in the ventromedial/ventral half of the somite are influenced by Shh and noggin
In response, the ventral somite cells express Pax1 and Pax9 -- induces proliferation and epithelium to mesenchyme transformations
The newly formed mesenchymal cells is the scleratome
How does scleratome mesenchyme become a vertebrae?
Resegmentation: the cranial half of one somite merges with the caudal half of the next adjacent somite
As a result, vertebrae become intersegmental with respect to the orignal somite segmental pattern.
Skeletal muscles derived from dermomyotomes can span adjacent vertebrae
What does the central subdomain of scleratome tissue produce?
What does the Ventral subdomain of scleratome tissue produce?
Vertebral body, IV disc
What does the Dorsal subdomain of scleratome tissue produce?
Dorsal part of neural arch, spine
What does the Lateral subdomain of scleratome tissue produce?
What does the Somitocoel subdomain of scleratome tissue produce?
Vertebral joints, IV disc, proximal ribs
Cells from the cranial half of scleratome contribute to:
Vertebral body, small parts of neural arch and distal rib
Cells from the caudal half of the scleratome contribute to:
Vertebral body, transverse process, most of neural arch and proximal part of main part of distal rib
What do cells from the cranial and caudal parts of the scleratome form?
Cranial half forms vertebral body, small parts of neural arch and distal rib
Caudal half forms vertebral body, transverse process, proximal rib, main part of distal rib and main part of neural arch
What gene determines the type of vertabra that will form and where it will form?
And retinoic acid
By what method do vertebra become bone?
How do the ribs form?
Costal processes expand laterally
Proximal portion of rib forms from cells of central scleratome and somitocoel
Distal portion is derived from lateral scleratome cells
How does the sternum form?
Begins independently as cartilage bars on either side of midline
Derived from Somatic mesoderm
Bars fuse after embryo folding
Secondary segmentation forms Sternebrae
Refusion of sternebrae forms body of sternum
Cranial most sternebrae forms manubrium
Xiphoid process forms at caudal end
What is hemivertebrae?
A remainder of a vertebra that did not form completely
What is spina bifida?
Series of conditions where one or a few adjacent vertebrae have unfused spinous processes
Spina bifida occulta is the mildest form, asymptomatic
What is sacrilization?
Occurs if fifth lumbar vertebrae is incorporated into sterum
What is Kippel-Feil sequence?
Characterized by presence of several fused cervical vertebrae
Neck is shortened, low nuchal hair line
Limited spine mobility
Associated with genitourinary and cardiopulmonary defects and hearing loss
What is scoliosis?
Abnormal curvature of the spine
Congenital form may be caused by hemivertebrae
Seven times more common in females
What is lumbarization?
When the first sacral vertebra is not included in the sacrum
What is Rachischisis?
A condition where many or all vertebrae have unfused spinous processes