Bone formation

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Bone formation with images

What are the two methods of bone formation?

1. intramembranous ossification 2. endochondral ossification

Which method of bone formation is referred to as being direct, and why?

intramembranous ossification- because there is no cartilaginous template as in endochondral ossification

Which method of bone formation is referred to as being indirect, and why?

endochondral ossification- because a cartilaginous template is formed prior to ossification

Explain the sequence of intramembranous bone formation.

1. mesenchymal cells condense into a connective tissue membrane
2. mesenchymal cells differentiate into osteoblasts, osteoid is secreted and forms bone spicules
3. calcium phosphate salts are incorporated into osteoid matrix, osteoblasts are surrounded and become osteocytes
4. spicules continue to develop, the spaces inbetween form the marrow cavity, the outer and inner membranes undergo compaction
5. remodelling

What types of bones are normally formed by intramembranous formation?

flatbones, ie. of the skull

What is meant by endochondral ossification?

bones are formed from a cartilage model

Where does endochondral ossification initially occur?

in the primary ossification center

Which type of bone normally exhibits endochondral ossification?

long bones

What is the first step in endochondral ossification?

a fetal template of hyaline cartilage is formed

Why is the first step in endochondral ossification important?

must have template of cartilage for ossification to occur, the template is a model for what is to come

What is the next critical step in endochondral ossification?

calcification of the perichondrium

Where is the primary center of ossification located?

in the diaphysis

What occurs at the primary center of ossification?

osteoclasts resorb bone spicules to form marrow cavity, osteoblasts form new bone

How does the marrow cavity form in endochondral ossification?

by the action of osteoclasts resorbing bone spicules

Where do the secondary centers of ossification occur?

in the epiphysis

What is the region dividing the primary and secondary centers of ossification called?

epiphyseal plate

What steps form the general process involved in growth of long bones?

continued production of cartilage at the epiphyseal plate in the metaphysis region causes elongation - endochondral ossification

What type of bone growth is responsible for increase in width?


What type of bone growth is responsible for increase in length?


Why do long bones stop growing in length?

hormonal control of cartilage production at the epiphyseal plate stops

How does the stoppage of long bones growing in length occur?

the epiphyseal plate stops producing new cartilage cells, the ossification front from the primary ossification center ossifies the plate which is then resorbed by osteoclasts

What is formed as a result of the stoppage of long bones growing in length?

a confluent marrow cavity

How is the stoppage of long bones growing in length controlled?

hormones: gonadal and growth

What is involved in the healing of bone fractures?

callus formation: clotted blood replaced by connective tissue, then endochondral ossification

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