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