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Blood calcium regulation and bone remodeling
Although bones do not seem to change much once
adulthood is reached bones continue to remodel themselves throughout life
bone remodeling is a continual changes in bone resulting from
changes in blood calcium levels and gravitational and muscular forces pulling
on bones
Let's start with some vocabulary
for bone remodeling. Hypocalcemia
low levels of calcium in the blood
Hypercalcemia
high levels of calcium in the blood
Osteoblast: bone-building cells that deposit
calcium in the bone matrix. Osteoclasts
bone destroying cells that remove calcium from the bone matrix and release it
into the bloodstream
to control blood calcium levels
osteoblasts and osteoclasts regulate the deposition
and dissolving the bone. When blood calcium levels drop below normal
PTH or parathyroid hormone is released into the blood
osteoclasts are stimulated to break down bone matrix
blood calcium levels then rise
when blood calcium levels become too high
calcium is deposited into the bone matrix by osteoblasts
thus lowering the calcium levels in the blood back to the normal range
for bones to retain their proportions and strength
as they grow bones must be remodeled
bones grow in length at the epiphyseal plate and articular cartilage
and grow appositionally in the periosteum
if the bone is not remodeled after growth,
its proportions and thickness are abnormal. Osteoclasts remodel the bone to restore
its normal thickness
Bone is reabsorbed from the outside and inside the phone shaft
due to the remodeling process bones can retain their proportions and thickness
as they grow
Bone remodeling can also occur during adulthood in response to gravitational
forces and the pull muscles
in the center
we see an average bone. Left
their is a thinner bone. Bones that are not exposed to much stress become thinner
and lighter
Less bone matrix is deposited by osteoblasts. On the right
there's a thicker bone. Bones grow thicker in certain areas in response to stress
Osteoblasts deposit more bone matrix in areas of the bone
exposed to more stress