Bone Change
• Increased or decreased diameter of medullary
canal
• Increased or decreased width of the cortical
bone
• Changes in the mineral content of the tissue
• Changes in length, girth, and density of the
bone tissue
Ossification
Closing of the epiphyseal plates
Earlier in women
Bone Growth
• Internal layer of periosteum builds new
concentric layers on old layers
• Simultaneously, bone around sides of the
medullary cavity is reabsorbed so that
diameter is continually increased
• Osteoblasts - cells that form new bone
• Osteoclasts - cells that absorb old bone
Bone Properties
• Composed of calcium carbonate, calcium
phosphate, collagen, & water
– 60-70% of bone weight - calcium carbonate &
calcium phosphate
– 25-30% of bone weight - water
• Collagen provides some flexibility & strength
in resisting tension
• Aging causes progressive loss of collagen &
increases brittleness
Healthy Bone Remodeling
Occurs Where…
• Experiencing growth
• Mechanical stress
• Microfractures
• Breaks
• 20% of bone tissue is replaced annually by
remodeling process
• 5 phases in the process
– Activation
– Resorption
– Reversal
– Formation
– Quiescence
Activation
1. Pre-osteoclasts are attracted to the
remodeling sites.
2. Pre-osteoclasts fuse to form multinucleated
osteoclasts.
Resorption
3. Osteoclasts dig out a cavity called a
resorption pit, in spongy bone, or burrow a
tunnel in compact bone.
4. Calcium can be released into the blood for
use in various body functions.
5. Osteoclasts disappear.
Reversal
6. Mesenchymal stem cells, pre-cursors to
osteoblasts, appear along the burrow or pit
where they…
7. proliferate (increase in numbers) and
differentiate (change) into preosteoblasts,
then …
Formation
8. mature into osteoblasts at the surface of the
burrow or pit and ...
9. release osteoid at the site, forming a new soft
nonmineralized matrix.
Quiescence
10.The new matrix is mineralized with calcium
and phosphorous.
11. The site, with resting lining cells, remains
dormant until the next cycle.
H:\Kinesiology\Bones
Joints\watch.htm
http://www.youtube.com/watch?v=0dV1Bw
e2v6c
Osteoid
• Organic part of the matrix composed of
proteoglycans, glycoproteins, and collagen
fibers
• Bone structure
• Flexibility and tensile strength that allow the
bone to resist against stress