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Embryology Exam II > Skeletal System Development > Flashcards

Flashcards in Skeletal System Development Deck (27):

What is derived from mesodermal sclerotomes/somites?

-vertebral column




What is derived from later plate mesoderm?

-limb bones



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.



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?



-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


-a branch of a specific cranial nerve



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


How does the chondrocranium/neurocranium form?

-ossification centers form within the cartilage allow continued growth and are separated from each other by synchondroses -> growth is due to Shh

-membranous components may be incorporated into the endochondral components

-bones of the neurocranium arise as a result of inductive interactions if surrounding mesenchyme -> characterized by transient appearance of type II collagen and cartilage specific proteoglycan

-intersection of more than two bones form fontanelles

-fusion of sutures


What transcription factors are involved in the closure of the sutures?

FGF-2 -blocked-> Noggin -blocked -> BMP -> closure of sutures

-Noggin is expressed in all sutures


What's the difference between a suture and a fontanelle?

-a suture is when two structures fuse together

-a fontanelle is when more than two structures fuse together