Bone is a rigid connective tissue and functions as a mechanical support and ion reserve for metabolic functions.

• It consists of cells and matrix. Bone matrix is made up of 40% organic component and 60% of inorganic component.
• Organic constituents include type I collagen, proteoglycans, noncollagenous proteins osteocalcin,osteonectin and osteopontin.
  

• Inorganic contents include predominantly calcium and phosphorous in the form of calcium hydroxyapatite and osteocalcium phosphate.
• The cellular components include osteoblasts, osteoclasts and osteocytes. Osteoblasts synthesize the bone matrix and are derived from osteoprogenitor cells. Osteoclasts are bone resorbing cells which are
  derived from the monocytes.
• Osteocytes are inactive osteoblasts that have become trapped within the bone matrix.
• Bone is divided macroscopically into compact and trabecular types.
• Compact bone or cortical bone is thick and dense and forms the outer part of the bone proper.
• It provides mechanical support to the bone. Mature compact bone  consists of lamellae that form concentric rings around larger longitudinal canals called Haversian canals.
• Haversian canals run parallel to the surface and along the long axis of the bone.
  

• The canals and the surrounding lamellae are called a Haversian system or an osteon.
• A Haversian canal generally contains one or two capillaries and nerve fibres.
• Haversian canals are interconnected by horizontally placed canals called Volkmann’s canals
• Trabecular bone, also known as cancellous bone or spongy bone, forms the inner part of the bone and helps in metabolism.
• They are highly vascular and contains red or yellow marrow depending on the age of the individual.
• The functional unit of cancellous bone is the trabecula.
• Trabecula are arranged as a network and are few cell layers thick.
• There are no blood vessels within the matrix of spongy bone but are well nourished from the adjacent blood vessels in the marrow spaces.