development MSK Flashcards
(39 cards)
What are the layers of the mesoderm? Medial to lateral
Notochord, Paraxial mesoderm, Intermediate mesoderm, Lateral Plate mesoderm
The somite comes from the paraxial mesoderm.
Name the derivatives of the somite?
What are their functions?
Sclerotome (cartilage) Syndetome (tendons) Myotome (skeletal muscle) Dermatome (dermis, skeletal muscle) Endothelial cells (dorsal aorta)
When does paraxial mesoderm become somites?
End of week 3
How many pairs of somites are there?
Initially 38-39 pairs
After 5 weeks: 42-44
What part of somite does the SCLEROTOME come from?
Ventromedial part (through EMT)
What part of somite does the DERMOMYOTOME come from?
Dorsal part
It eventually splits into dermatome and myotome
What part of somite does the SYNDETOME come from?
Intermediate part
between sclerotome and myotome
What region of the sclerotome does the VERTEBRAL BODY come from?
Ventral Region
makes sense because it is closest to notochord and will wrap around
What region of the sclerotome does the VERTEBRAL ARCH AND SPINE come from?
Dorsal Cells
will surround neural tube
What region of the sclerotome does the TRANSVERSE PROCESS AND RIBS come from?
Lateral cells
How are sclerotomes subdivided in cranial/caudal portions?
Cranial= loose packed
Caudal= densely packed
Divided by intersegmental boundary (aka von Ebner’s fissure)
Due to gene expressivity and cell density
When do sclerotome cells condense around notochord?
End of week 4
How is a centrum formed?
dense (caudal) cells merge with loose (cranial) cells from next caudal sclerotome.
Where do intersegmental arteries lie?
On each side of the vertebral body
Why do we have 8 cervical nerves but only 7 cervical vertibrae?
Because the sclerotome from the occipital bone lies above C1
What becomes part of the nucleus pulposus?
The notochord. If it is not lost by adult, will form a cordoma (cancer)
What forms annulus fibrosis?
the caudal cells forming circular fibers around nucleus pulposis
When/ Where do ribs form?
During week 5. On costal processes of T vertebrae
cartilaginous during embryo, ossify during fetal period
Where do sternal bars arise from?
somatic layer of lateral plate mesoderm
When and in what direction do sternal bars fuse?
10 weeks. ventrolateral and move medially
What axis do Hox genes code for?
cranial-caudal (vertebral identity)
What gene is important at thoracic/ lumbar junction?
Hox10 (stops rib formation)
What can cervical ribs cause?
thoracic outlet syndrom.
Impinge on brachial plexus and/ or subclavian artery –> paresthesia
What is Pectus excavatum?
‘Funnel chest’
Depressed sternum, sunken posteriorly.
From extra cartilage weight
(more common in male)