Osteoblasts and Osteoclasts

What are osteoblasts and osteoclasts?

Osteoblasts and osteoclasts are cells in your body that help your bones grow and remodel to stay strong.

Your bones are living tissue like any other part of your body. It might not seem like it, but they’re constantly growing or changing and reshaping themselves throughout your life.

You might only think of bones growing and changing in children and teens. But osteoblasts and osteoclasts play important roles in helping your bones stay healthy and strong, even after your bones reach their adult size.

Osteoblasts and osteoclasts work together to form new bone cells and break down old or damaged bone tissue. Osteoblasts form new bone tissue. Osteoclasts break down old bone tissue to make room for new, healthier tissue to replace it.

What do osteoblasts do?

Osteoblasts are like construction crews that build new bone cells. You might see them called osteogenic cells. They strengthen your existing bones and help form new bone tissue.

Osteoblasts have three main functions:

• Growing new bones (bone formation).
• Reshaping bones to help them change as you age (remodeling).
• Healing damaged or broken bones.

Osteoblasts are triggered by chemical reactions or hormones when a bone grows or changes. They create and release (secrete) a mix of proteins called bone matrix. Bone matrix is made of proteins like collagen mixed with calcium, phosphate and other minerals.

After they’re activated, osteoblasts move into place and deposit bone matrix in spaces on a bone that needs to grow or be strengthened or repaired. After it’s in place, the bone matrix solidifies and hardens into new, healthy bone. Picture a worker pouring concrete. They might create a whole new sidewalk. But they can also use that same concrete to patch cracks or broken chunks in an existing path. In this example, osteoblasts are the worker, and bone matrix minerals are the concrete they use to create new bone.

Once the osteoblasts have completed their job of laying down new bone tissue, they can then become part of the bone by transforming (differentiating) into osteocytes, or they die (if they’re no longer needed).

Osteocytes act like a security system inside your bones. They’re the most common type of cell in your bones. They monitor changes in pressure and stress that affect your bones. They respond to everything from normal movement and the force of you using your body to more intense changes like injuries. They can send signals to the osteoclasts and osteoblasts to repair damaged bone tissue. For example, if a bone is cracked, damaged or broken, osteocytes trigger a reaction that attracts osteoclasts to dissolve the area around the break (to resorb damaged bone tissue) and osteoblasts to lay down new bone tissue, so it can begin to heal.

What do osteoclasts do?

Osteoclasts dissolve and break down old or damaged bone cells. They make space for osteoblasts to create new bone tissue in areas that are growing or need repair.

If osteoblasts are builders, osteoclasts are your bones’ demolition crew. Think clasts for cleaners and blasts for builders. Osteoclasts release enzymes that break down old bone. They trigger chemical reactions on the surface of old bone tissue that dissolves it and creates space for newer, stronger tissue to form in its place.

Osteoclasts dissolve bone tissue, but it’s not as violent or aggressive as acid eating a hole in metal in a cartoon. The process of breaking down areas of old tissue is tightly regulated or controlled and specific. Osteoclasts only target specific areas that have been tagged by osteocytes.

The enzyme osteoclasts release breaks down hardened bone matrix and reabsorbs it into your body. This leaves microscopic pits and divots on the surface of your bone. Once the targeted tissue in those places is dissolved, osteoblasts move in and deposit new bone in the same spot.

What do osteoblasts and osteoclasts look like?

Osteoblasts and osteoclasts are tiny cells found along the bone lining and in the bone itself.

Osteoblasts are shaped like cubes — they’re slightly box-shaped.

Osteoclasts are bigger than osteoblasts. They’re shaped like rounded domes.

What are the common conditions and disorders that affect osteoblasts and osteoclasts?

Osteoblasts and osteoclasts are important parts of your overall bone health. Any condition that affects your bones can impact the cells in them, too. Some of the most common issues that affect your ability to grow and maintain strong bones include:

• Osteoporosis.
• Osteopenia.
• Hyperparathyroidism.
• Paget’s disease of the bone (osteitis deformans).

Which tests are done to osteoblasts and osteoclasts?

Usually, you won’t need any tests done to check on your osteoblasts or osteoclasts. Healthcare providers generally use tests for your bones to check the health of your whole bone rather than looking for specific cells. But sometimes they run labs to see how your osteoclasts are working or to help them diagnose and treat osteoporosis.

More common tests for bone health include:

• A bone density test: A bone density test measures how strong your bones are with low levels of X-rays. It’s called a DXA scan. Bone density tests can measure bone loss as you age or check for signs of osteopenia and osteoporosis.
• Vitamin D 25-hydroxy test: They’ll check to see if you’re getting enough vitamin D.
• Calcium: They’ll check your blood level and do a 24-hour urine calcium screen.
• Intact parathyroid hormone (IPTH).
• Creatinine: They’ll check your kidney function with a creatinine test.

How do I keep my bones healthy?

There are things you can do to help keep your bones healthy. Some tips include:

• Follow a nutritious diet and weight-bearing exercise plan.
• Avoid smoking.
• Be sure you’re getting enough calcium and vitamin D.
• See a healthcare provider for regular checkups and contact them if you aren’t feeling well.

What is the difference between osteoblasts and osteocytes?

Osteoblasts and osteocytes are both cells that help you grow and maintain bones.

Osteoblasts are the cells that form new bones and grow and heal existing bones. They release bone matrix that turns proteins into new tissue. Bone matrix fills in gaps and spaces in your existing bone tissue.

Osteocytes are cells inside mature bone tissue. They respond to changes in tension and pressure in and around your bones. If something puts enough pressure on your bone, osteocytes trigger a chemical reaction that alerts osteoblasts and osteoclasts to repair damage and grow new bone in an affected area.

A note from Cleveland Clinic

Osteoblasts and osteoclasts are tiny cells that have a big impact on your bone health. They constantly work in a rhythm of growth and repair to keep your bones healthy. They automatically cycle your bones through their growth and development.

It’s important to see a healthcare provider for routine check-ups. People who are over age 65, who’ve gone through menopause or have chronic medical conditions may need more frequent visits. Healthcare providers can monitor your bone health for bone loss and osteoporosis.