Ossification and Joints Flashcards
What is ossification?
The replacement of connective tissue by bone.
What happens when mineralisation fails?
Osteomalacia
How does mineralisation fail?
Lack of Ca2+ in the diet or malabsorption from the small intestinal disease results in poor mineralisation of bones
How are bones formed in the foetus?
The replacement of pre-existing CT by bone
What are the two types of ossification?
Intramembranous and endochondral
What type of bones does intramembranous ossification form?
flat bones
Where does intramembranous ossification occur?
Ossification occurs within a “membrane” of primitive mesenchymal cells
Describe stage one of intramembranous ossification/
Mesenchymal cells differentiate into osteoblasts
A cluster of osteoblasts form an ossification centre and lay down osteoid
Describe stage 2 of intramembranous ossification
Mineralisation of osteoid occurs within a few days to produce an island of bone
Trapped osteoblasts become osteocytes
Describe stage 3 of intramembranous ossification?
Islands of bone join to form trabeculae of woven bone with blood vessels
Mesenchyme cells condense at edges to form periosteum
Describe stage 4 of intramembranous ossification
Increased bone formation occurs on outer and inner surfaces to produce plates of bone
Spongy bone persists internally and red marrow develops in the trabecular spaces
What is endochondral ossification?
Involves the ossification of a hyaline cartilage template
Hyaline is deposited in the shape of the required bone within a mass of mesenchymal tissue
When does endochonral ossification occur?
Begins in the second month of foetal development
What is endochondral ossification used for?
Forms the long bones of the body
What is the epiphysis?
The club shaped ends of the “bone” templates