Bone is a metabolically active tissue composed of several types of cells
These cells include osteoblasts, which are involved in the creation and mineralization of bone tissue, osteocytes, and osteoclasts, which are involved in the reabsorption of bone tissue
Osteoblasts and osteocytes are derived from osteoprogenitor cells, but osteoclasts are derived from the same cells that differentiate to form macrophages and monocytes
Within the marrow of the bone there are also hematopoietic stem cells. These cells give rise to other cells, including white blood cells, red blood cells, and platelets
- Osteoblasts are mononucleate bone-forming cells
- They are located on the surface of osteon seams and make a protein mixture known as osteoid, which mineralizes to become bone
- The osteoid seam is a narrow region of newly formed organic matrix, not yet mineralized, located on the surface of a bone
- Osteoid is primarily composed of Type I collagen
- Osteoblasts also manufacture hormones, such as prostaglandins, to act on the bone itself
- The osteoblast creates and repairs new bone by actually building around itself
- First, the osteoblast puts up collagen fibers
- These collagen fibers are used as a framework for the osteoblasts’ work. The osteoblast then deposits calcium phosphate which is hardened by hydroxide and bicarbonate ions
- The brand new bone created by the osteoblast is called osteoid
- Once the osteoblast is finished working it is actually trapped inside the bone once it hardens
- When the osteoblast becomes trapped, it becomes known as an osteocyte
- Other osteoblasts remain on the top of the new bone and are used to protect the underlying bone, these become known as lining cells