67. histogenesis of bone (bone formation)

Question 1

What 2 ways can bone be formed

Answer 1

Endochondral- the hyaline cartilage is eroded and invaded by osteoblasts starting osteoid production

Intramembranous- osteoblasts differentiate directly from mesenchyme and secrete osteoid. Occurs in frontal and parietal bones

Question 2

Which are the 2 stages in endochondral ossification

Answer 2

primary ossification stage

secondary ossification stage

Question 3

for endochondral ossisfication, where are the 2 regions the cartilage remains

Answer 3

layer of articular cartilage in joints

epiphyseal cartilage which connects the epiphysis to diaphysis

Question 4

In both ossification processes, which bone is formed first

Answer 4

woven bone then replaced by stronger lamellar bone

Question 5

Describe the primary ossification process (at the diaphysis)

Answer 5

• osteoblast activity surrounds cartilage model
• cartilage degrades due to lack of nutrients
• chondrocytes produce alkaline phosphatase, compresses matrix leading to ossisfication
• chondrocytes die = porous structure from remamnce of collagens of ECM
• osteoblasts adhere to this and form primary layer of bone

Question 6

Describe the secondary ossification process (at epiphysis)

Answer 6

• bone enlarges and arranges itself in rows
• matrix begins to increase in quantity
• calcareous material deposisted
• matrix becomes more calcified

Question 7

Describe intramembranous ossification

Answer 7

• embryonic mesenchymal tissue
• within condensed layer of mesenchyme, there are ossification centres
• the mesenchymal cells differentiate to osteoprogenitor cells and form incomplete layers of osteoblasts around network of capillaries

Question 8

What is epiphyseal cartilage for?

Answer 8

responsible for the growth in length of the bone and disappears upon completion of bone development at adulthood.

Occurs at different times in different bones but by 20 bones stop growing

Question 9

What are the 5 zones of epiphyseal cartilage plates

Answer 9

• ZONE OF RESERVE CARTILAGE- or resting cartilage as there is no proliferation. Consists of hyaline cartilage
• ZONE OF PROLIFERATION- chondrocytes show mitotic activity and arranged into columns
• ZONE OF HYPERTROPHY- hypertrophic cells arranged in columns. Enlarged chondrocytes compresses ECM
• ZONE OF CALCIFIED CARTILAGE- undergoes degeneration process. Chondrocytes show signs of apoptosis
• ZONE OF OSSIFICATION- ossification of bone, osteoclasts, osteoblasts, capillaries, progenitor cells contributes.