Bone Development and
Growth
Ossification
The process by which bone
forms.
Bone Development
• Begins in first two months of prenatal life.
• 2 methods – 1. Intramembranous ossification,
formation directly on or within fibrous connective
tissue. 2. Endochondral ossification,
formation of bone within cartilage.
• Both methods lead to the same structure in
mature bone
• Different methods of development in which both
replace preexisting connective tissue with bone.
Intramembranous Ossification
• Flat bones of the skull, the mandible and
clavicles form this way.
1. Cells in the mesenchyme ( tissue that all
other connective tissue arise), come
together and form precursor cells
(osteoprogenitor) transform into
osteoblasts, capable of secreting collogen
and mineral salts.
Intramembranous
2. Osteoblasts cluster and become active by
secreting new organic matrix around
themselves.
3. After secretion stops the cells now called
osteocytes are located in the lacunae,
extend narrow cytoplasmic processes into
canaliculi.
4. Within a few days mineral salts have been
deposited and the matrix hardens.
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Intramembranous
Bone matrix develops into trabeculae
Which fuse to form spongy bone
The spaces between the trabeculae fill
with red marrow
The mesenchyme develops into periostem
Eventually most spongy bone is replaced
by compact bone except at the center of
the bone.
Endochondral Ossification
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1.
Bones that form from cartilage.
All other bones
Begins around 6th week of life
At site where bone will be, cells come
together to shape the future bone.
2. Cells develop into cartilage producing
cells (chondroblasts) that change into
hyaline cartilage. (cartilage model)
Endochondral
3.The cartilage models grows and thickens
4. Blood vessels penetrate it, causing some
chondroblasts to die while others transform into
osteoblasts.
5. Death of chondroblasts leaves spaces in the bone,
in long bone this happen in the center of the
diaphysis, called the primary ossification center.
6. Osteoblasts migrate to the spaces and produce
spongy bone. At the same time periosteum cells
deposite a thin layer of compact bone, on the surface
of the model (cartilage).
Endochondral
7. Now more blood vessels penetrate the
model at the epiphysis.
8. In a long bone this is known as the
Secondary ossification center.
9. The conversion of the cartilage to bone
happens again, in the epiphysis.
Endochondral
10. The space formed by the cartilage
destruction, expands to form a medullary
cavity.
11. The epiphysis fills with spongy bone with
a thin layer of compact bone surrounding,
the walls of the diaphysis thickens.
12. A thin layer of cartilage remain between
the epiphysis and the diaphysis, called the
epiphyseal plate
Animations of both forms of
ossification
http://www.douglas.bc.ca/ossification/files/ossification1.html
Bone Growth- Interstitial
• Lengthwise (interstitial) growth- epiphyseal plate
• Cartilage region that contains chondroblasts that
produce new cells and intercellular material,
pushed toward epiphysis.
• At the other end of the plate the cartilage in
regenerating itself.
• Bone will continue to grow as long as the
chondroblasts are active. ( regulated by
hormones)
• Epiphseal line is a permanent fuse of the
epiphysis and the diaphysis
Bone Growth- Appositional
• Width growth of a long bone
• Osteoblasts in the periosteum, deposite new
compact bone along the outer surface of the
diaphysis.
• Medullary cavity expands by destruction of the
bone along the inner surfaces, performed by
osteoclasts (dissolve bone matrix, be secreting
enzymes)
• Unequal process, more bone deposited then
removed, making a thicker and stronger bone.
Bone remodeling
• Bone does not become inactive once it is done
growing.
• Osteoblasts deposit new bone, osteoclasts
reabsorb old bone.
• The process is known as bone remodeling.
• Not all bones undergo it, but bones and sections
of bones that undergo the most stress or injuries
undergo it more frequently.