Tuesday, April 15, 2008

Bone Growth, Remodeling, and Repair

Introduction: After taking a look at the skeletal system, let's take a closer look at bones. This section is going to discuss the cells involved in bones, bone growth, remodeling, repair, and the breaking down of bones as well.

Cells Involved:

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

~Intramembranous Ossification:

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

Called calcification

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

~Endochondral Ossification

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

~Final Size

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.


*Bone Remodeling

~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

Bone Repair:

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.

*Bone Repair

~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

Three weeks

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 cavity


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

Behind them

~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.


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