Bone Cells Types and Function - What Do Bone Cells Do?

Mahmud Hassan, Jay Mallonee
  • Author
    Mahmud Hassan

    Central University of Punjab has taught Earth Science for over 20 years. They have a Master's of Science in Geology, Geography, and Environmental Science. They also have other courses such as pharmaceutical, life sciences, history, etc. , .

  • Instructor
    Jay Mallonee

    Jay is a wildlife biologist, college professor and writer. His master's degree is in neurobiology and he has studied animal behavior since 1976.

Learn about bone cells. Understand bone cell function and the role of osteogenic cells in bone formation. Identify what the four types of bones are. Updated: 11/10/2021

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Bone Cells

What are bone cells? These cells are the ones in the body that contribute to the growth, structure, maintenance, and function of the bone tissue. These cells collectively comprise less than 2 percent of the bone mass. However, they are very important to the function of bones.

Bone cells vary greatly in their structure and function. A bone cell can be mono-nucleated or multi-nucleated. The shape of the bone cells can also vary. They can be flat, round, cubical and columnar, stellar, or pancake-like in shape. The bone cells most commonly found in the bone tissue generally have protoplasmic projections and lacunae or small chambers. These dendritic projections of specialized bone cells ultimately form a system of tiny canals called canaliculi.

Bones are important components of the skeletal system that provide structure and support for the body. They are generally hard due to their tough extracellular matrix. Bones function to protect the vital organs of the body and also enable the movement or locomotion of an individual. Four different types of bone cells ensure bone health by regulating the formation, growth, and maintenance of the bone tissue. These four types of cells are osteocytes, osteoclasts, osteoblasts, and bone lining cells.

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  • 0:00 Bone Cells:…
  • 0:36 Osteogenic Bone Cells
  • 2:00 Osteoblast Bone Cells
  • 3:27 Osteoclast Bone Cells
  • 5:04 Osteocyte Bone Cells
  • 5:46 Lesson Summary
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Skeletal system of humans

The skeletal system of humans is shown. Different types of bones providing a structure to the body are shown.

Osteogenic Cells

Before we dive into the four types of bone cells, we need to first learn what osteogenic cells are. These cells, sometimes called osteoprogenitor cells, are the immature cells found in deep layers of the periosteum and the bone marrow. These mono-nucleated cells appear squamous or flattened in structure and have high mitotic activity. They are undifferentiated cells that can divide by mitosis, and differentiate into specialized types of cells. Since one of the types of cells these can differentiate into are bone cells, osteogenic cells act as stem cells of the bone.

In response to stimulation, some of these bone stem cells act as precursors of osteoblasts and undergo a differentiation process to give rise to the bone-forming osteoblasts. Other osteogenic cells may turn into different types of cells altogether, such as fat cells. At a later stage, the cells that turned into osteoblasts further transform structurally to form mature types of bone cells called osteocytes.

What are the Four Types of Bone Cells?

Bones consist of four basic types of cells: osteoblasts, osteocytes, osteoclasts, and bone lining cells. Each bone cell type has a specific structure and performs unique functions. In this section, you'll learn what these bone cells do.

Colorized scanning electron micrograph shows bone cells

A colorized scanning electron micrograph shows bone cells adhering to a new type of bone cement.

Osteoblasts

Osteoblasts are mono-nucleated, cube-shaped bone cells that arise from the osteogenic cells. They are commonly found in the growing periosteum and endosteum portions of the bone tissue. The membrane surrounding a bone is termed the periosteum, while the membranous vascular layer of cells lining the medullary cavity is called the endosteum. Osteoblasts, in their inactive state, resemble the flat appearance of osteogenic cells.

This type of bone cell mainly promotes the uptake of minerals such as calcium and phosphorus that are essential for bone structure. These bone cells generally secrete a matrix composed of collagen fibers and calcium-binding proteins to form the new bone tissue called osteoid. Collagen is a protein majorly found in the bone structure and needs to be secreted for the deposition of a bone matrix. As the matrix calcifies, the osteoblasts in its surroundings get trapped within the matrix itself. As a result, osteoblasts undergo structural changes and, therefore, form another type of bone cell called osteocytes. Some of them may even differentiate to form the bone lining cells.

Osteocytes

Osteocytes are mono-nucleated mature bone cells. These cells are formed from the embedding of osteoblasts in the bone matrix. As a consequence, lacunae or small cavities are incorporated into the bone structure. They are one of the most common types of bone cells. They have protoplasmic projections along with lacunae or small chambers. The dendritic projections ultimately form a system of tiny canals called canaliculi. Osteocytes help in the maintenance of bone structure by regulating the mineral concentration of the bone matrix. The osteocytes vary in shape with respect to that of the lacunae, causing them to have an irregularity in their shapes. As osteocytes meet their end, the surrounding matrix eventually gets reabsorbed.

Osteoclasts

Osteoclasts are the multinucleated bone cells formed from the fusion of two or more hematopoietic stem cells found in the bone marrow. The hematopoietic stem cells are also responsible for the formation of macrophages. Thus, osteoclasts are sometimes called osteophages. They are bone-dissolving cells that trigger the release of bone minerals into the bloodstream when these mineral levels decline in the blood for any reason. These bone cells are usually found at sites where osteolysis or bone resorption takes place.

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Frequently Asked Questions

What can osteogenic cells differentiate into?

Osteogenic cells can differentiate into another type of bone cell such as an osteoblast, in response to a stimulus. These bone-forming cells may further give rise to osteocytes and bone lining cells.

What is the role of osteogenic cells in bone repair?

In response to the stimuli such as bone injury or damage, osteogenic cells can give rise to osteoblasts that are responsible for the formation of bone structure. Osteoblasts further form cells called osteocytes that maintain the bone structure by regulating the mineral concentration of the matrix.

What are the function of bone cells?

Osteoblasts are responsible for bone formation, and osteocytes help maintain bone structure by regulating the mineral concentration of the matrix. Osteoclasts are responsible for bone resorption, while bone lining cells are believed to play a complementary role in maintaining the bone matrix.

What are the 4 types of bone cells?

Four types of bone cells are osteoblasts, osteocytes, osteoclasts, and bone lining cells. Osteoblasts are formed from osteogenic or osteoprogenitor cells, and further transform into osteocytes. Osteoclasts arise from hematopoietic stem cells. Bone lining cells are occasionally formed from the osteoblasts that neither differentiate to osteocytes nor undergo programmed cell death.

Are osteogenic cells stem cells?

Yes, osteogenic cells are undifferentiated bone cells that can divide and differentiate in response to some stimulation. They mainly form different types of bone cells including osteoblasts or osteocytes. Thus, these cells are sometimes referred stem cells of the bone.

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