Bone Formation, Growth, and Remodeling

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1. Formation and Growth Bone forms via a process called ossification

or osteogenesis As an embryo we all have a loose hyaline

cartilage skeleton that eventually hardens and becomes our skeleton

Over time (sixth or seventh week of embryonic development) osetoblasts form a bone matrix over the cartilage, and over time the internal hyaline cartilage center is digested and converted into the marrow cavity.

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2. Bone Growth Occurs at the epiphysial plate in a lengthwise

direction New cartilage is added at the diaphysis side

of the epiphysial plate, and as it grows it hardens

New bone cells replace the cartilage, ossify, and die becoming bone along the way

Bones thicken at their periosteum as they grow lengthwise

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Growth Continued New cells secrete collagen and Ca ions, These new cells will stack up on top of

each other and form a matrix New blood vessels are enclosed with a

layer of tissue, and new bone is created over the top.

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3. What does bone do when it is finished growing? Bone responds to two things: Changes

in calcium levels, or the pull of gravity on muscle tissue.

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Calcium Changes If blood Calcium levels drop, PTH

(parathyroid hormone) is released. This will activate more osteoclast

activity This increased activity will lead to the

breakdown of bone and the ultimate release of Calcium back into the bloodstream for use.

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Calcium changes cont. If blood Calcium levels increase,

(Hypercalcimia) PTH levels will decrease

This will cause a decrease in the level of osteoclast activity

This in turn leads to the deposition of Calcium into bone matrix.

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Stresses from Exercise and Activity Stress forces bone to constantly

remodel itself It will lay down new bone and destroy

old bone in areas where stress is applied most often.

This will lead to an increase in bone thickness which strengthens the bone

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Cont. If you become inactive for an extended

period of time the opposite takes place. Less activity leads to a decrease in

bone remodeling This will thin the bones out And over time these bones can become

brittle and easy to damage or break.

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