Skeletal System Development Flashcards
What is derived from mesodermal sclerotomes/somites?
- vertebral column
- ribs
- sternum
What is derived from later plate mesoderm?
- limb bones
- girdles
What is derived from the head mesoderm?
-calvaria and base of skull
What is derived from neural crest cells?
-facial bones
What interacts in the limb skeleton?
-continuous interaction between apical ectoderm all ridge and limb bud mesoderm
What interacts in the vertebral column?
-inductive interaction between sclerotome and notochord or neural tube
What interacts in the head bones?
- interaction between preskeletal neural crest cells and information along migratory paths
- interactions between areas of the brain and overlying mesenchyme
What is the common pathway of bone/cartilage differentiation?
- mesenchyme is induced to enter the common pathway
- production of N-cadherins which promote mesenchymal cell condensation
- TGF-beta stimulates synthesis of fibronectin and N-CAM
- aggregated state of mesenchymal cells is stabilized
Describe the membranous bone pathway.
- requires transcription factors Runx-2 and Osx
- mesenchymal cells differentiate into osteoblasts
Describe the permanent cartilage pathway.
- mesenchymal condensation forms chondroblasts
- Sox-9 causes chondroblasts to secrete collagen II and cartilage matrix
- Sox-9 is continually expressed in permanent cartilage
Describe the endochondral bone pathway.
- Runx-2, ihh, and BMP-6 induce cartilage to undergo hypertrophy
- hypertrophic cartilage cells secrete bone proteins and vascular endothelial growth factor
- invading blood vessels erode the hypertrophic cartilage and bring in osteoblasts to replace cartilage with bone
What is the centrum derived from?
-derived from ventral and medial parts of paired sclerotomes
Skeletal tissue is _______________ in origin.
Mesenchymal
What do the neural arches arise from?
-arise from dorsal regions of sclerotomes
What are the costal processes/ribs derived from?
- proximal development depends on expression of myotomic myogenic factors, Myf-5 and Myf-6
- distal development depends on BMP signals from somatopleural mesoderm
What Hox genes create the boundaries in the ribs and vertebra?
Hox 3: occipital-cervical boundary
Hox 6: cervical-thoracic boundary
Hox 9: attached floating ribs boundary
Describe the development of the sternum.
- derived from lateral plate mesoderm
- arises as a pair of cartilaginous bands
- fused cartilaginous bands secondarily subdivide into craniocaudal elements
Describe the development of the clavicle.
- arises from neural crest
- follows intramembranous pathway
- one of first bones to become ossified
What are the three structures the developing skull is composed of?
- neurocranium
- viscerocranium
- occipital sclerotomes
What is the neurocranium?
- part of the skull that surrounds the brain
- has a cartilaginous portion and a membranous portion
-base is formed from the chondrocranium (cartilage)
+origin of occipital, sphenoid, ethmoid, and parts of temporals
-membranous part:
+origin of part of occipital, parietals, frontal so, and part of temporals
What is the viscerocranium?
- surrounds oral cavity and pharynx
- has a cartilaginous portion and a membranous portion
-cartilaginous portion forms:
+pharyngeal arch I (Meckel’s cartilage, malleus, incus)
+pharyngeal arch II (Reichert’s cartilage, stapes, styloid)
-membranous portion:
+part of temporal, zygomatic, maxillary, nasal, lacrimal, alatine, vomer, ptygoid plates, mandible, tympanic ring
Describe the pharyngeal arches in the viscerocranium.
- mesenchymal that forms the viscerocranium is mostly from neural crest
- 6 pairs of pharyngeal arches
What are the 4 components that each pharyngeal arch consists of?
- skeletal element
- muscles
- a branch of a specific cranial nerve
- artery
Basioccipital portion of chondrocranium is derived from _________ cartilages and _____________ sclerotomes.
- parachordal cartilages
- occipital sclerotomes
- other components of the original cartilages fuse to form final chondrocranium
