Difference Between Osteoblasts and Osteocytes

The key difference between osteoblasts and osteocytes is that osteoblasts are a type of bone cells responsible for the formation of new bones while osteocytes are a type of bone cells that maintain the bone mass.

Bone is a living and growing tissue that makes the skeleton of humans and other vertebrates. It consists of different cell types like osteoblasts, osteocytes, osteoclasts, and bone lining cells. These cells perform different functions within the bone. Osteocytes are responsible for maintaining the bone mass while osteoblasts are responsible for the formation of new bones. On the other hand, osteoclasts are responsible for the resorption of the bone. All these three processes – formation, sustenance, and resorption – occur continuously in the bone tissue in order to protect the structural integrity of the skeletal system and balance the calcium and phosphorus levels in the body.

CONTENTS

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

What are Osteoblasts?

Osteoblasts are a type of bone cells. They are the bone-forming cells that carry out bone deposition. They secrete an organic matrix that is rich in collagen protein. Collagen protein is a bone-forming protein. Moreover, osteoblasts are important in controlling the calcium and phosphorus levels in the body. Osteoblasts also have a role in the regulation of bone resorption.

Osteoblasts originate from the mesenchymal stem cells. Generally, osteoblasts are immature cells, but differentiated cells. Furthermore, osteoblasts cells are found on the surface of the new bone. They have only one nucleus. Osteoblasts then become mature and convert into osteocytes, which are essential for maintaining bone matrix.

What are Osteocytes?

Osteocytes are a type of bone cells present inside the mature bones. They are star-shaped cells with projections. The size of a cell body of an osteocyte may vary from 5-20 micrometers in diameter. A mature osteocyte consists of a single nucleus. There are about 42 billion osteocytes in an average human body. These cells contain an average half-life of 25 years. The osteocytes inhabit spaces called lacunae. Moreover, osteocytes originate from osteoblasts. Once osteoblasts get trapped inside the matrix which they secrete themselves, they develop and mature into osteocytes. Furthermore, osteocytes are interconnected and networked to each other through long cytoplasmic extensions.

Osteocytes are able to carry out molecular synthesis, modification, distant signal transmission. Thus, their functions are similar to the nervous system. Mature osteocytes carry out the majority of important receptor activities in bone function. Furthermore, osteocytes are considered as a major regulator of bone mass and an endocrine regulator in phosphate metabolism. There are several factors affecting the death of osteocytes. They are necrosis, senescence, apoptosis or engulfment of osteoclasts. In addition, osteocyte destruction may cause a disease called osteoporosis.

What are the Similarities Between Osteoblasts and Osteocytes?

• Osteocytes and osteoblasts are two types of bone cells.
• They are living cells.
• Furthermore, they are differentiated cells.
• Also, they are parts of an osteon.
• Osteocytes are formed from osteoblasts.

What is the Difference Between Osteoblasts and Osteocytes?

Osteoblasts and osteocytes are bone cells. However, the key difference between osteoblasts and osteocytes is their function. That is; osteoblasts are responsible for bone formation while osteocytes are responsible for the maintaining bone matrix. Furthermore, another difference between osteoblasts and osteocytes is that the osteoblasts are immature cells while the osteocytes are mature cells. Moreover, osteoblasts are formed from stem cells (osteogenic stem cells) while osteocytes are formed from osteoblasts.

A further difference between osteoblasts and osteocytes is their location. Osteoblasts are present on the surface of new bones. Osteocytes reside in the lacunae (inside of the bone). In addition, osteoblasts do not have projections while osteocytes characteristically have projections. Hence, this is a structural difference between osteoblasts and osteocytes.

Summary – Osteoblasts vs Osteocytes

In summarizing the difference between osteoblasts and osteocytes, osteoblasts and osteocytes are two types of bone cells. But, osteoblasts are immature bone cells that become mature and convert into osteocytes.  Moreover, osteoblasts are responsible for bone formation while osteocytes are important for maintaining the bone mass or the matrix. Furthermore, osteoblasts originate from mesenchymal stem cells while osteocytes originate from osteoblasts. Also, osteoblasts are present on the surface of the new bones while osteocytes are present inside the bones in lacunae.

Reference:

1. “Osteoblast.” Wikipedia, Wikimedia Foundation, 1 Apr. 2019, Available here.
2. Schaffler, Mitchell B, et al. “Osteocytes: Master Orchestrators of Bone.” Calcified Tissue International, U.S. National Library of Medicine, Jan. 2014, Available here.

Image Courtesy:

1. “604 Bone cells” By OpenStax College – Anatomy & Physiology, Connexions Web site, Jun 19, 2013 (CC BY 3.0) via Commons Wikimedia
2. “Transverse section of bone en” By Source digital bitmap graphics: BDBRecreated in vector format: Nyq – Original analog graphics: Gray’s Anatomy of the Human Body from the classic 1918 publication available online at Bartleby.com.Digital bitmap graphics: Transverse Section Of Bone.pngRecreated in vector format: Own work (CC BY-SA 4.0) via Commons Wikimedia