Difference Between Osteoblasts and Osteoclasts

The key difference between osteoblasts and osteoclasts is that the osteoblasts are a type of bone cells that form new bones while osteoclasts are another type of bone cells that dissolve bones.

Bones are a component of our skeletal system.  It is a hard, but resilient tissue that is unique to vertebrates. The main functions of bones are to protect internal organs and to provide rigid support for muscle attachment. There are three types of cells in bone tissue: osteoblasts, osteoclasts, and osteocytes. Osteocytes are mature osteoblasts, and they do not secrete bone matrix. Moreover, the function of the osteocyte is to maintain metabolism and exchange nutrients and eliminate wastes. Osteoblasts are the bone forming cells while osteoclasts have the opposite function of osteoblasts, which is bone resorption. Hence, these two cell types control the rates of the formation and breakdown of bone or bone remodeling.

CONTENTS

1. Overview and Key Difference
2. What are Osteoblasts 
3. What are Osteoclasts
4. Similarities Between Osteoblasts and Osteoclasts
5. Side by Side Comparison – Osteoblasts vs Osteoclasts in Tabular Form
6. Summary

What are Osteoblasts?

Osteoblasts are small, mononucleate cells that are responsible for bone formation. They have the ability to synthesize collagen matrix, where mineralization takes place. In addition, these cells are important for maintenance, growth, and repair of bones. In bones, only osteoblasts possess parathyroid hormone (PTH) receptors.

When osteoblasts are activated by PTH, osteoblasts release cytokines that directly and indirectly stimulate osteoclasts, which ultimately increase the number and activity of osteoclasts. The origin of osteoblasts is osteoprogenitor cells located in the periosteum and bone marrow.

What are Osteoclasts?

Osteoclasts are another type of bone cells that are large and have some unique ultrastructure characteristics such as multiple nuclei, abundant mitochondria and a large number of vacuoles and lysosomes. Furthermore, the presence of sealing zones and ruffled borders is a characteristic feature of osteoclasts.

The main function of osteoclasts is the resorption and degradation of bone; hence, they help to remodel the bone while destroying bone cells and reabsorbing calcium. In addition, osteoclasts help to maintain blood calcium concentrations at optimal levels. In the bone remodeling process, osteoblasts mediate the actions of osteoclasts through cytokines.

What are the Similarities Between Osteoblasts and Osteoclasts?

• Osteoblasts and osteoclasts are two types of bone cells.
• They come from bone marrows.
• Moreover, they are found on the surface of the bones.
• Also, both involve in the bone remodeling.

What is the Difference Between Osteoblasts and Osteoclasts?

Osteoblasts are a type of bone cells that form new bones while osteoclasts are a type of bone cells that dissolve bones. So, this is the key difference between osteoblasts and osteoclasts. Further to this, a significant difference between osteoblasts and osteoclasts is that the progenitors of osteoblasts are derived from pluripotent mesenchymal stem cells whereas those of osteoclasts are derived from hematopoietic cells of granulocyte-macrophage lineage.

Moreover, osteoblasts mediate the activities of osteoclasts by releasing cytokines. Furthermore, osteoblasts possess receptors for parathyroid hormone (PTH)but not the osteoclasts. Therefore, we can consider this also as a difference between osteoblasts and osteoclasts. Besides, an important functional difference between osteoblasts and osteoclasts is that the osteoblasts promote the formation of bones while osteoclasts promote the bone breakdown.

In addition, osteoblasts become osteocytes whereas osteoclasts do not. Also, another difference between osteoblasts and osteoclasts is that the osteoblasts are smaller and mononucleate whereas osteoclasts are larger and multinucleate.

Below infographic summarizes the difference between osteoblasts and osteoclasts, comparatively.

Summary – Osteoblasts vs Osteoclasts

Among the three types of bone cells, osteoblasts and osteoclasts are two types that are important in bone remodeling. Osteoblasts are small mononucleated cells that form new bones while osteoclasts are large multinucleated cells that dissolve bones. Osteoblasts are able to become osteocytes, the third type of bone cells, while osteoclasts are cannot. Furthermore, osteoblasts can mediate the activity of osteoclasts, releasing cytokines. Thus, this is a summary of the difference between osteoblasts and osteoclasts.

Reference:

1. Caetano-Lopes, Joana, et al. “Osteoblasts and Bone Formation.” Acta Reumatologica Portuguesa, U.S. National Library of Medicine, 2007, Available here.
2. Teitelbaum, Steven L. “Osteoclasts: What Do They Do and How Do They Do It?” The American Journal of Pathology, American Society for Investigative Pathology, Feb. 2007, Available here.

Image Courtesy:

1. “604 Bone cells” By OpenStax College – Anatomy & Physiology, Connexions Web site. Available here, Jun 19, 2013 (CC BY 3.0) via Commons Wikimedia
2. “Osteoclast1” By Cellpath (talk) – Cellpath (talk) (CC BY-SA 3.0) via Commons Wikimedia