Dr. Gillaspy has taught health science at University of Phoenix and Ashford University and has a degree from Palmer College of Chiropractic.
Osteoblasts & Osteoclasts: Building & Repairing Bones
When you were little, your parents might have decorated your room with things that babies like, but as you got older, the same choo-choo trains and baby dolls that you once thought were great probably didn't seem so cool anymore. If you were lucky, your parents let you remodel your bedroom so it was better suited for a teenager. Well, your taste in room decorations is not the only thing that changes as you get older; so do your bones. In this lesson, you will learn about how your bones start to form and how they remodel, or change, throughout your life thanks to some special cells.
Ossification & Osteoblasts
The bones you have now started out as cartilage, which is a flexible type of connective tissue. You still have some of this cartilage. You can find it at the bridge of your nose, on parts of your ribs and at your joints, but for the most part, the 'cartilage bones' you started out with turned into 'bony bones' by the time you were crawling around on your own. This process of making bone is called ossification.
One thing you will notice is that when we talk about things related to bone, we often use the prefix 'os-' or 'osteo-'; keeping that fact in mind might help you recall some of the terms we will be using in this lesson. It's also good to keep in mind that the suffix '-tion' is used to describe an action, like creation or formation, so ossification is literally bone formation.
The change from cartilage to bone is the work of osteoblasts, which are bone-building cells. To remember this term, you will want to recall the Bs, meaning 'blasts build.'
In your first few months of life, there was a lot of ossification going on, and your osteoblasts were hard at work replacing the flexible cartilage with the hard deposits that make up your bones. This happens in all parts of your bones except for two areas. One is at the ends of your bones where cartilage remains throughout life to help your joints glide smoothly.
The other area where cartilage remains is known as the growth plates. These are basically the growing zones of bones because these are the areas of your bones that allow them to get longer. As you know, you get taller as you move from being a child to a teenager; during this same time your arms get longer to keep pace with the rest of your body. This lengthening is thanks to the activity taking place at your growth plates. As you finish up your teen years, these growth plates seal off and completely change into bone, which is why you stop growing as an adult.
Remodeling & Osteoclasts
While your osteoblasts might not stay as busy as they were when you were first born, they do stay active throughout your life because your body remodels your bones as conditions change, just like you remodel your bedroom as your tastes change. One thing that might convince your bones that it's time to remodel is changes in the amount of calcium in your blood. As it turns out, your bones are your body's favorite place to store calcium. Calcium is a mineral that makes your bones strong, but it's also needed elsewhere in your body for things like helping to send messages through your nervous system and contracting your muscles.
Your body needs to keep a certain amount of calcium in your blood so that it's readily available when it's needed for these other jobs. If the calcium level in your blood drops too low, it steals some from your bones with the help of another type of bone cell called osteoclasts. These are bone-destroying cells that break down or chew up your bones to meet the needs of your body. To remember this term, you will want to recall the Cs, meaning 'clasts chew.'
Another thing that tells your bones it's time to remodel is physical stress. As you grow and gain weight, your bones have to get stronger and denser to support you. Can you guess which bone cells would help out here? If you guessed osteoblasts, then you're right. The osteoblasts build bone to deal with the stress of the added weight. So what do you think would happen if you got really sick and couldn't get out of bed for a few months? Well, there would be less stress on your bones, so they would not have to be as strong. In this case, osteoclasts would chew up bone, leaving them weaker.
There is one other type of stress that your bones can endure that I hope you never have to experience, and that is a bone fracture. If a bone does break, we see the osteoblasts spring into action to build new bone and repair the damage, and we also see osteoclasts lending a hand to get rid of old bone and sculpt and shape the new bone so it looks good as new.
Let's review. The bones start out as cartilage, which is a flexible type of connective tissue. They later go through the process of making bone called ossification with the help of osteoblasts, which are bone-building cells.
Ossification is delayed at the growth plates, which we could call the growing zones of bones because these are the areas that allow bones to get longer as a child grows up. These growth plates close at the end of the teen years, but your body remodels your bones throughout life as conditions change. For example, if the calcium level in your blood drops too low, it steals calcium from your bones with the help of osteoclasts, which are bone-destroying cells that chew up your bones.
Another thing that tells your bones it's time to remodel is physical stress. For example, as you grow bigger, your osteoblasts lay down more bone to support the added weight. If a bone breaks, osteoblasts repair the damage, while osteoclasts lend a hand to sculpt and shape the new bone.
After learning about osteoblasts and osteoclasts in this lesson, take the opportunity to pursue these goals:
- Remember that the cartilage of infants solidifies into bone as they develop
- Discuss bone structure changes through ossification
- Understand the purpose of growth plates
- Explain the function of osteoclasts and osteoblasts
- Specify the causes of bone remodeling in adulthood
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