Osteoblasts vs Osteoclasts
The skeletal system is basically made up bones. Bone tissue is considered as 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 considered as mature osteoblasts, and they do not secrete bone matrix. The function of the osteocyte is to maintain the metabolism and to exchange nutrients and eliminate wastes. Osteoblasts are the bone forming cells while osteoclasts have the opposite function of osteoblasts. Hence, these two cell types control the rates of formation and breakdown of bone or bone remodeling.
Osteoblasts are small, mononucleate cells, 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 bone, 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 from osteoprogenitor cells located in the periosteum and in the bone marrow.
Osteoclasts have some unique ultrastructure characteristics, such as multiple nuclei, abundant mitochondria and a large number of vacuoles and lysosomes. The most characteristic feature of osteoclasts is the presence of sealing zones and ruffled borders. The sealing zones (or clear zones) are made up of thick band of actin that serves for the establishment of osteoclasts to the bone surface and for the isolation of the resorption area from the surroundings. The main function of osteoclasts is resorption and degradation of bone; hence they help to remodel the bone while destroying bone cells and reabsorb calcium. In addition, osteoclasts help to maintain blood calcium concentrations at optimal levels. In the bone remodeling process, the actions of osteoclasts are mediated by osteoblasts through cytokines.
Osteoblast vs Osteoclast
• Progenitors of osteoblasts are derived from pluripotent mesenchymal stem cells, whereas those of osteoclasts are derived from hematopoietic cells of granulocyte- macrophage lineage.
• Osteoblasts mediate the activities of osteoclasts by releasing cytokines.
• Osteoblasts possess receptors for parathyroid hormone (PTH), while osteoclasts do not.
• Osteoblasts promote the formation of bones while osteoclasts promote the bone breakdown.
• Osteoblasts become osteocytes, whereas osteoclasts do not.
• Osteoblasts are smaller and mononucleate, whereas osteoclasts are larger and multinucleate.