Bone Remodeling

•An embryo’s skeleton is
made of cartilage.

•Near the third month of
embryo development,
osteoblasts begin to
secrete mineral deposits
that replace the cartilage.
The osteoblasts then
mature into osteocytes.

•This process of
incorporating calcium &
minerals into cartilage to
become bone is known as
ossification.

•As a child grows, tall columns
of chondrocytes (cartilage
cells) at the epiphyseal plate
divide and then deteriorate
as the matrix around them
calcifies. These cells are
then known as osteoblasts,
which form spongy bone.

•Osteoclasts secrete acid to
enlarge the medullarycavity
as the bone grows so that
marrow is available for all
cells.

Inorganic

• 65% Mineral Salts
• Crystalline salts made

of hydroxyapatites

• Ca10(PO4)(OH)2

• Provides bone strength

& hardness.

• Lack of hydroxyapatite

causes “Rickets”

Organic

• 35% Osteoid (made of

ground substance &
collagen)

• Provides the flexibility &

tensile strength required
to keep bones from
constantly breaking.

• Lack of collagen causes

“Brittle Bone Disease”

•Because calcium is so
important in your body, a
certain level needs to be
maintained in your blood at all
times. To maintain that level,
bone is created or dissolved.

•Think of your bones as a
storage tank for calcium.

•There are 2 hormones
(secreted chemicals) that
trigger these processes:
•Calcitonin (from the Thyroid
gland)

•Parathyroid Hormone (PTH)
(from the Parathyroid glands)

1) Hematoma forms

Blood enters the
wound. Cells
begin to die.
Phagocytes ingest
dead bone cells
and debris.

2) Callus forms

Blood vessels
grow. Cartilage
forms to hold the
bone together.

3) Callus ossifies

Spongy bone
forms to replace
the cartilage.

4) Compact bone forms

Osteoclasts form a
larger medullary
cavity.
Spongy bone is
converted to
compact bone.