Main Difference – Osteoblast vs Osteoclast
Osteoblast and osteoclast are two types of cells found in the bone. Both of these cell types are involved in the repair of broken bones. Osteoblasts and osteoclasts differ in their function in the maintenance of bones. The main difference between osteoblast and osteoclast is that osteoblast is involved in the formation and mineralization of bones whereas osteoclast is involved in the breakdown and resorption of bones. The osteogenic cells in bones are developed into osteoblasts. The osteoblasts secrete the collagen matrix and the calcium salts of a bone. When osteoblasts are trapped inside the bone by calcification, they are transformed into the more mature type of bone cells called osteocytes. The osteoclasts are developed from either monocytes or macrophages.
Key Areas Covered
1. What is an Osteoblast
– Definition, Characteristics, Function
2. What is an Osteoclast
– Definition, Characteristics, Function
3. What are the Similarities Between Osteoblast and Osteoclast
– Outline of Common Features
4. What is the Difference Between Osteoblast and Osteoclast
– Comparison of Key Differences
Key Terms: Bone, Bone Breakdown, Bone Formation, Bone Resorption, Calcification, Mineralization, Osteoblast, Osteoclast, Osteocytes, Osteogenic Cells
What is an Osteoblast
An osteoblast is a type of bone-forming cell, which is involved in the formation and mineralization of bones. Osteoblasts help in both initial bone formation and later bone remodeling processes. These cells are found as a closely packed, sheath of cells on the surface of the bone. Osteoblasts are developed from osteogenic cells in the periosteum. The periosteum is the tissue that covers the outer surface of the bone. Osteoclasts can also be found in the endosteum of the marrow cavity. Many products of osteoblasts such as growth factors, collagen, hormones such as osteocalcin, and enzymes such as collagenase and alkaline phosphatase are involved in the bone formation. The unmineralized part of the bone is called osteoid.
Figure 1: Bone Cell Types
Once the osteoblast is surrounded with its growing matrix, the cells are trapped in a space called lacuna. These trapped osteoblasts become mature bone cells called osteocytes. Osteocytes can communicate with the bone surface and receive nutrients through long, meandering channels called canaliculi. The four types of bone cells and their functions are shown in figure 1.
What is an Osteoclast
An osteoclast refers to a type of bone cell responsible for the bone resorption. Since bone is a dynamic tissue, the continuous formation and breakdown occur in it. Bone breakdown can occur in response to the calcium requirement of calcium. That means bones serve as a calcium reservoir in the body. The continuous destruction of bones is mediated by osteoclasts. Osteoclasts are found on the surface of bones. The small depressions on the bone surface which are occupied by osteoclasts are called Howship lacunae. These small depressions are formed by the action of enzymes secreted by osteoclasts. Osteoclasts are derived from circulating cells such as monocytes and macrophages. They can be derived from the bone marrow as well.
Figure 2: Osteoclast
Osteoclasts are multinucleated cells with about 200 nuclei per cell. Many of the osteoclasts comprise around 5 to 20 nuclei per cell. Microvilli are extended from osteoclasts to the bone surface, forming a brush-like structure at the active sites of bone resorption. The acid phosphatases secreted by the osteoclasts dissolve both collagen, calcium, and phosphorus in the bone. First of all, the bone is broken down into small fragments, which are then engulfed by osteoclasts. The digestion of the fragments occurs in the cytoplasmic vacuoles inside the osteoclast cells. The calcium and phosphorous produced by the demineralization of bones are released into the blood stream. Osteoclasts do not work on the osteoid. An osteoclast in an area of bone resorption is shown in figure 2.
Similarities Between Osteoblast and Osteoclast
- Both osteoblast and osteoclast are two types of cells found in the bone.
- Both osteoblast and osteoclast are involved in the repair and breakdown of bones.
- Both osteoblasts and osteoclasts are found on the surface of bones.
Difference Between Osteoblast and Osteoclast
Definition
Osteoblast: An osteoblast is a bone-forming cell that is derived from the mesenchymal osteoprogenitor cells and is involved in the bone remodeling processes.
Osteoclast: An osteoclast is a type of bone cell that is responsible for the bone resorption.
Developed from
Osteoblast: Osteoblasts are developed from the osteogenic cells.
Osteoclast: Osteoclasts are developed from monocytes or macrophages.
Size of the Cells
Osteoblast: Osteoblasts are smaller, uninucleated cells.
Osteoclast: Osteoclasts are large, multi-nucleated cells.
Role
Osteoblast: Osteoblasts are involved in the formation and mineralization of bones.
Osteoclast: Osteoclasts are involved in the bone breakdown and bone resorption.
Conclusion
Osteoblast and osteoclast are two types of cell found in the bone, functioning in bone remodeling. Osteoblasts are developed from osteogenic cells while osteoclasts are developed from monocytes or macrophages. Osteoblasts are the cells that are involved in the bone formation and the mineralization of bones. Osteoclasts are the cells that are involved in the breakdown and resorption of bones. Therefore, the main difference between osteoblast and osteoclast is the function of each type of bone cell in bone remodeling.
Reference:
1.“Cell Types in Bones.” Boundless, 23 June 2016, www.boundless.com. Available here. Accessed 18 Aug. 2017.
2.“Osteoblast.” Encyclopædia Britannica, Encyclopædia Britannica, inc., Available here. Accessed 18 Aug. 2017.
3.“Osteoclast.” Encyclopædia Britannica, Encyclopædia Britannica, inc., Available here. Accessed 18 Aug. 2017.
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. “استئوکلاست” By Navid.drogba – Own work (CC BY-SA 4.0) via Commons Wikimedia
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