Lect. 22 - Skeletal System Devpt. I

Question 1

What parts of the skeleton originate in the lateral plate mesoderm?

Answer 1

Limb bones and girdles

Question 2

What parts of the skeleton originate in the head mesoderm?

Answer 2

Calvaria and base of skull

Question 3

What parts of the skeleton originate in the neural crest?

Answer 3

Facial bones

Question 4

Describe the common pathways of the bone/cartilage differentiation pathways

Answer 4

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.

Question 5

Describe the membranous bone pathway of the bone/cartilage differentiation pathways.

Answer 5

Requires TFs Runx-2 and Osx; mesenchymal cells differentiate into osteoblasts

Question 6

Describe the permanent cartilage pathway of the bone/cartilage differentiation pathways.

Answer 6

Mesenchymal condensation forms chondroblasts; Sox-9 causes chondroblasts to secrete collagen II and cartilage matrix; Sox-9 is continually expressed in permanent cartilage.

Question 7

Describe the endochondral bone pathway of the bone/cartilage differentiation pathways.

Answer 7

Runx-2, ihh, and BMP-6 induce this 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 w/ bone

Question 8

Origin of the centrum

Answer 8

Derived from ventral and medial parts of paired scleretomes

Question 9

Origin of neural arches

Answer 9

Arise from dorsal regions of sclerotomes

Question 10

Origin of costal processes/ribs

Answer 10

Proximal development depends on expression of myotonic myogenic factors, Myf-5 and Myf-6; distal development depends on BMP signals from somatopleural mesoderm

Question 11

Occipital-cervical boundary

Answer 11

Hox 3

Question 12

Cervical-thoracic boundary

Answer 12

Hox 6

Question 13

Attached-floating ribs boundary

Answer 13

Hox 9

Question 14

What is the origin of the sternum?

Answer 14

Derived from lateral plate mesoderm; arises as a pair of cartilaginous bands that fuse then subdivides into craniocaudal elements

Question 15

What is the origin of the clavicle?

Answer 15

Arises from neural crest; follow intramembranous pathway; one of the first bones to become ossified

Question 16

What parts of the skeleton originate in the mesodermal scleretomes (of somites)?

Answer 16

Vertebral column, ribs, sternum