The fundemental structural unit of compact bone. Osteons are roughly cylindrical tubes.

• Lamella - weight bearing, column-like matrix tubes composed mainly of collagen
• Central canal/Haversian - Central channel containing blood vessels and nervs
• Volkmann's canals - chanells lying at right angles to the central canal, connecting it to the blood and nerve supply of the periosteum

Hydroxyapatite (mineral form of calcium)

• 65% of bone by mass
• Responsible for the hardness of bone and its resistance to compression

• Osteoblasts: uninuculeated cell that forms bone osteoid, bone-forming cells
• Osteoid: unmineralized portion of the bone matrix prior to maturation of bone tissue. It is composed of proteoglycans, glycoproteins, and collagen.
• Osteocytes: 95% of bone cells in the body. They are osteoblasts that have become surrounded by mineralized bone.
• Lining cells: quiescent osteoblasts lining the surface of the periosteum
• Osteoclasts: large cells that resorb or break down bone matrix

• Cuboidal shaped, central nucleus on bone surface, gap junctions with neighboring osteoblasts for communication b/t cells
• Come from bone marrow precursor cells. These precursors are capable of turning into either osteoblasts or fat cells, and various factors determine which kind of cells will be made.
• The function of osteblasts is to make the proteins that will form the organic matrix of bone and to control mineralization of the bone.
• Fates after making new bone:
• Some become surrounded with bone matrix and differentiate into osteocytes
• Others will remain on the surface of the new bone and differentiate into lining cells
• The rest undergo apoptosis and disentregrate from proteins from other cells.

• Former osteoblasts which have become flat and pancake-shaped.
• Line the entire surface of the bone
• Are responsible for the immediate release of calcium from the bone if the blood calcium level is too low.
• Protects the bone from chemicals in the blood which dissolve crystels (e.g. pyrophosphate)
• Have receptors for hormones and factors that initiate bone remodeling.

• Located in the bone unlike the other bone cells.
• The osteocyte network plays an endocrine role in phosphate regulation and vitamind D metabolism.
• Osteocytes initiate the bone remodeling process.
• Osteocyte apoptosis is impacted by estrogen loss after menopause.
• Osteocyte apoptosis is induced by systemic glucocorticoids.
• Osteocytes are positively impacted by physical activity (decrease apopptosis).

• Large cells with many nuclei
• They resorb bone. They form sealed compartments next to the bone surface and secrete acids and enzymes which degrade the bone. The edge next to the bone is called the ruffle border.
• After they finish resorbing bone they undergo apoptosis, regulated by proteins from other cells.