Bone Structure

Bone Structure in General Bone is a type of connective tissue It is as strong as steel but as light as aluminum It is a moist living tissue that constantly breaks down and rebuilds itself Each bone adjusts its shape and size during the growing process, after injury, and in response to stress A bone’s shape makes possible its functions Bony projections called processes provides sites of attachment for ligaments and tendons Grooves and openings are passageways for blood vessels and nerves

Parts of a Long Bone Long bones are divided into three regions Epiphysis Metaphysis Diaphysis

Epiphysis Is the expanded portion at the end of each long bone It forms a joint (articulates) with another bone The proximal epiphysis is the end nearest the torso The distal epiphysis is the end farthest from the torso The outer surface of the epiphysis is covered with a layer of hyaline cartilage called articular cartilage

Diaphysis & Metaphysis The diaphysis is the shaft of the long bone The metaphysis is the widening part of the bone between the epiphysis and diaphysis

Internal Long Bone Structure Long bone consists of a porous central cavity surrounded by a ring of dense material The layers from the outside to the inside of bone are: Periosteum Compact bone Spongy bone Medullary cavity Endosteum Marrow

Periosteum Is a tough membrane that covers the surface of the bone It doesn’t cover the articular cartilage on its ends It contains a network of blood vessels and nerves, which supply nutrients and signal pain

Compact Bone Is a hard thick layered material that enables bone to endure large amounts of stress It makes up the wall of the diaphysis It is also known as cortical bone Its extracellular matrix is continuous with no gaps

Spongy Bone Composes mainly the epiphysis of bone It is also known as cancellous bone It consists of many branching bony plates called trabeculae Irregular connecting spaces between the trabeculae help reduce the bone’s weight The bony plates are most highly developed in the regions of the epiphyses subjected to compressive forces

Medullary Cavity, Endosteum, & Marrow In the diaphysis, compact bone forms a semi-rigid tube with a hallow chamber called the medullary cavity This cavity is continuous with the spaces of spongy bone A thin membrane containing bone-forming cells, called the endosteum lines it A specialized connective tissue known as marrow, fills it Marrow comes in two forms red & yellow

Internal Long Bone Structure

Microscopic Structure of Compact Bone Compact bone is composed of cylinders of mineral crystals and protein fibers called lamellae In the center of each lamellae is a narrow channel called a Haversian canal Blood vessels run through interconnected Haversian canals, supplying nourishment to the bone tissue Wrapped around each Haversian canal are layers of protein fibers Haversian canals are connected to each other via Volkmann’s canals, which carry a blood vessel, nerve, and lymph vessel

Microscopic Structure of Compact Bone Embedded within the large gaps between the protein layers are bone cells, known as osteocytes Each osteocyte is embedded in fluid filled cavities called, lacunae and surrounded by concentric layers of bone matrix, lamellae The lamellae and lacunae together form an osteon The lacunae are connected to one another and to Haversian canals by a system of interconnecting canals called canaliculi

Internal Bone Structure