Lecture 1 - Skeletal development

Question 1

What is the diaphysis?

Answer 1

The diaphysis is the central shaft of the bone made up of:

• cortical bone
• bone marrow (red and yellow)
• adipose tissue

Question 2

What is the Epiphysis?

Answer 2

The rounded end of the long bone:

• joint with adjacent bone covered with articular cartilage
• filled with red bone marrow (produces RBC)

Question 3

What is the Metaphysis?

Answer 3

Wide portion of the long bone between epiphysis and diaphysis:
- contains growth plate

Question 4

Mesenchyme

Answer 4

Embryonic tissue which develops into connective and skeletal tissues (incl. blood and lymph)

Question 5

Three stages of joint formation

Answer 5

Interzone appearance:

• tri-laminar structure
• two cartilaginous outer layers separated by intermediate later (flattened mesenchymal cells)

Morphogenesis:

• beginning of the shape
• prenatal movements important

Cavitation:

• physical separation of rudiments
• mechanical forces essential

Question 6

Intramembranous ossification

Answer 6

Direct mineralisation:
MSCs (mesenchymal stem cells) differentiate into osteoblasts - secrete osteoid matrix

Forms most of compact bone (ribs, skull)

Question 7

Endochondral ossification

Answer 7

Cartilage replaced by mineralised tissue:

• Chondrocytes enlarge and secrete cells for mineral deposition
• calcification of matrix
• apoptosis of chondrocytes
• blood vessels invade and bring hematopoietic and osteoprogenitor cells
• osteoblasts use calcified matrix as a scaffold and secrete osteoid to form bone

Forms most of future cancellous bone - vertebral column, sternum

Question 8

Where are the primary and secondary centres of ossification?

Answer 8

Primary centre = first area of bone to ossify (e.g. diaphysis)

Secondary centre = appears after primary centre has already appeared (e.g. epiphyses)

Question 9

Long bone development

Answer 9

• bone collar forms around hyaline cartilage
• cavitation of cartilage
• invasion of internal cavities
• formation of the medullary cavity
• secondary ossification centres in epiphyses
• hyaline cartilage remains only in epiphyseal plates

Question 10

Skeletal growth prenatally and postnatally

Answer 10

Prenatally: longitudinal growth at the diaphyseal growth plates

Postnatally: epiphyseal and diaphyseal growth

Question 11

What happens when we stop growing?

Answer 11

Diaphyseal and epiphyseal centres of ossification meet. Growth plate is replaced by epiphyseal line

Question 12

Achondroplasia

Answer 12

Mutation in FGFR3 gene. Growth plate fuses early and can’t grow anymore

• limits progress of ossification
• common cause of dwarfism

Question 13

DDH Risk factors

Answer 13

• female
• family history
• ligament laxity
• breech
• lack of in utero fluid
• left hip
• large baby
• first born
• tight swaddling after birth