Skeletal system

Question 1

Origins of mesenchyme forming

1. axial skeleton
2. appendicular skeleton
3. head skeleton

Answer 1

1. Axial skeleton –> Sclerotome
2. Appendicular skeleton –> Lateral plate mesoderm
3. Head skeleton –> Neural crest cells

Question 2

Interaction between which two structures initiates skeletogenesis?

Answer 2

Sclerotome and notochord

Question 3

Intramembranous ossification

Answer 3

• groups of mesenchymal cells differentiate into osteoblasts
• secretion of bone matrix + ossification forming bone islands
• bone islands fuse

Question 4

Endochondral ossification

Answer 4

• MNEMONIC: Boys Can’t Pee During Erections
  1. Formation of bone collar when osteoblasts on surface secrete osteoid around center of cartilage plate

2. Cavitation - chondrocytes die leaving lacunae behind
3. Periosteal bud invasion - neurovascular bundle invades channels of bone, allowing osteoblasts to occupy where the chondrocytes were
4. Diaphysis elongates
5. Secondary centers of ossification appear and undergo the same processes on epiphysis of the bone

Question 5

Formation of neural arch

Answer 5

In week 4, sclerotome cells migrate to dorsal aspect of neural tube
they will form the neural arch

Question 6

Vertebral body of vertebrae formed by fusion of

Answer 6

Caudal aspect of sclerotome above with cranial aspect of sclerotome below

Question 7

when do chondrification centers appear in the vertebrae?

Answer 7

week 6

Question 8

number of chondrification centers in the developing vertebrae by the end of the embryonic period is

Answer 8

6; 2 in the centrum (future body)
2 in the neural arch
2 in the future transverse processes

Question 9

How does the number of ossification centers change before birth, after birth, and after puberty?

Answer 9

1. Before birth there are 3 ossification centers
   - one in the centrum (future body)
   - 2 on either side in each vertebral arch
2. After birth there are 5 centers of ossification
   - 2 at vertebral body
   - 2 on transverse processes
   - 1 on vertebral arch
3. After adolesence there are still 5 centers of ossification
   - 2 on the body
   - 3 on vertebral arch

Question 10

Spondylocostal dysostosis

Answer 10

short-trunk dwarfism (short torsos but normal-length arms and legs)
small chests that cannot expand adequately, often leading to life-threatening breathing problems.
inguinal hernia (due to increased intrabdominal pressure)
scoliosis

many affected individuals live into adulthood.