The picture below is from http://acadameic.kellogg.cc.mi.us. It shows how osteoblasts form and how they may differentiate into an osteocyte. Osteoblasts and osteocytes are what help build bone. Osteoclast does the opposite. It breaks it down, or reabsorbs it.
*Cells involved in bone growth
~Osteoblasts: bone-forming cells
~Osteocytes: mature bone cells from osteoblasts; maintain structure of bone
~Osteoclasts: bone-absorbing cells; break down the bone
Bone Development and Growth:
The above picture, from http://www.personal.psu.edu, demonstrates the different parts of a bone that critical to know.
*Bone Development and Growth
~Ossification: formation of bone
1. Examples: Flat bones; bones of the skull
2. Bones develop between sheets of fibrous connective tissues
3. Cells from connective tissue cells become osteoblasts
4. Osteoblasts secrete an organic mix
5. The bones harden when calcium salts add to the organic mix, a process
6. Osteoblasts promote calcification
7. Ends in the thin plates of spongy bone which contains red bone marrow
8. Periosteum forms outside of spongy bone and newly derived
osteoblasts further ossification
9. More thin plates form and fuse, becoming compact bone forming a
Bone collar that surrounds the spongy bone
1. Most bones of the human skeleton is formed this way
2. Bone replaces cartilaginous by calcified bone matrix
3. Inside, bone formations starts at center the spread to ends
1. Epiphyseal plates (growth plate) close and bone length no longer occurs
The above picture shows a growth plate and was found at http://www.eorthopod.com.
~Osteoclasts are constantly breaking down bone
~Osteoblasts reform them in the adult
~As much as 18% of the bone is recycled each year
~Bone remodeling is the process of bone renewal and keeps bones strong
For anyone that has broken a bone, they know it is a long process to repair a bone. Here is a picture from http://www.apatech.com that shows how a bone repairs itself.
~Four step process that occurs over several months
1. Hematoma: blood clots in the space between broken bones in about
Six to eight hours
2. Fibrocartilaginous Callus: tissue repair begins; fibrocartilaginous
Callus fills space between ends of broken bones for about
3. Bony Callus: Osteoblasts make thin plates of spongy bones and
Convert fibrocartilage callus to a bony callus and joins broken
Bones in about three to four months
4. Remodeling: Osteoblasts build new compact bone, osteoclasts absorb
Spongy bone which creates a new medullary cavityOsteoporosis:
Osteoporosis is a very serious problem. The picture below shows what a bone with osteoporosis looks like. It was found at http://www.cprevia.com.
~Condition where bones are weakened due to a decrease in the bone mass
That makes up the skeleton
~Bones build until the ones late twenties; by mid to late forties, body begins to
Give back what it has built and bone mass decreases
~Women are more susceptible to osteoporosis
~Leads to fractures
~Milk is not the only source. A great source is broccoli and cauliflower.
~Supplements are not always a great idea because there is not a lot of study
~Prevention includes taking in enough calcium during critical bone growth years
And engaging in weight bearing activities
Conclusion: Those are the many steps that a bone grows through. No matter what, when you get older, your bone will eventually give back some of the calcium it acquired. Remember to make sure you get enough calcium and there are definitely more sources than from milk. Now that we understand a little bit more about our bone structure, it is time to take a look at how we move it all around. The next section is very brief and discusses some of the vocabulary used to describe certain motions.