bone cells

Matrix of collagen fibers

cells entrenched there and provide a surface for inorganic salt crystals to adhere.

Salt crystals

form when calcium phosphate and calcium carbonate combine to create hydroxyapatite, which incorporates other inorganic salts like magnesium hydroxide, fluoride, and sulfate as it crystallizes, or calcifies, on the collagen fibers.

Hydroxyapatite crystals

give bones their hardness and strength, while the collagen fibers give them flexibility.

The 4 cells of the bone

Osteoblasts, Osteocytes, Osteogenic cells and Osteoclasts

Osteoblasts

• responsible for forming new bone

• found in the forming portions of the bone

• do not divide, synthesize and secrete the collagen matrix and calcium salts. 

• Osteoblast becomes trapped

• changes in structure and becomes an Osteocyte.

Osteocytes

• primary cell of mature bone and most common type

• located in the lacuna, surrounded by bone tissue

• maintain the mineral concentration of the matrix via secretion of enzymes.

• communicate with each other and receive nutrients via long cytoplasmic processes that extend through canaliculi

2 cells incapable of mitosis

Osteocytes and osteoblasts

Osteogenic cell

• are undifferentiated with high mitotic activity and they are the only bone cells that divide

• immature ones found in the deep layers of periosteum and the marrow

• differentiate and develop into osteoblasts.

dynamic nature of bone

new tissue is constantly formed, and old, injured, or unnecessary bone is dissolved for repair or for calcium release. 

Osteoclasts

• responsible for bone resorption, or breakdown

• originate from monocytes and macrophages, two types of white blood cells, not from osteogenic cells. 

relationship between osteoclasts and osteoblasts

ongoing balance between osteoblasts and osteoclasts is responsible for the constant but subtle reshaping of bone.