Bone Histology Terms

Appositional growth: Growth by the addition of new layers to the surface of those previously formed, as in the growth in diameter of cartilage and bone.

Bones: Components of the human skeleton, composed of a hard connective tissue with cells embedded in a mineralized matrix. Long bones are the elongated bones of the limbs. Short bones have nearly equal dimensions and include the carpals and tarsals. Flat bones are flattened, usually curved, and include most skull bones, sternum, ribs, and scapula. Irregular bones have complex shapes and include the vertebrae, coxal bones, and many facial bones.

Bone matrix: The extracellular organic material of bone tissue, including ground substance and collagen fibers, but excluding the inorganic calcium salts.

Bone remodeling: Process involving bone destruction and reformation, which occurs during growth and in response to hormones and mechanical stress factors.

Bone resorption: The removal of osseous tissue by osteoclasts, which can be part of the normal bone remodeling process, or for the maintainance of blood calcium ion homeostasis, or as part of a pathologic process.

Calcification: A process where tissue becomes hardened as the result of deposits of insoluble salts, such as hydroxyapatite; normally occurs only in the formation of bone and teeth.

Calcified cartilage: Cartilage tissue in which inorganic calcium salts are deposited in the matrix, which occurs prior to replacement by osseous tissue, and sometimes in aging cartilage.

Calcitonin: Hormone released by the thyroid gland that lowers blood calcium level and inhibits bone resorption

Chondroblast: A dividing cartilage-forming cell, derived from mesenchyme, that secretes a cartilaginous matrix and fibers, becomes enclosed in a lacuna, then differentiates into a chondrocyte.

Chondrocyte: Mature cartilage cell that occupies a lacuna within cartilage matrix.

Circumferential lamella: Bony lamella that encircles the outer and inner surface of a bone.

Compact bone: Dense bone tissue that forms the surface of bones; consists largely of concentric lamellar osteons.

Diaphysis: The rodlike shaft in the middle of a long bone, consisting of a bone collar surrounding a hollow medullary cavity, which is filled with yellow bone marrow in adults.

Endochondral ossification: Formation of osseous tissue by the replacement of calcified cartilage, which forms most fetal bones, and allows the growth in length of long bones.

Endosteum: Thin membrane that lines the medullary cavity of long bones and covers the trabeculae of spongy bone.

Epiphyseal line: The remnant of the epiphyseal plate in a long bone.

Epiphyseal plate: Plate of hyaline cartilage at the junction of the diaphysis and epiphysis of a long bone, which provides for growth in length.

Epiphyses: The ends of a long bone, consisting of an outer layer of compact bone surrounding internal spongy bone and red bone marrow.

Hydroxyapatite: The major inorganic calcium salt, Ca10 ( PO4 )6 ( OH )2 , that is found in bone.

Interstitial growth: Tissue growth from a number of different centers within a nonrigid matrix, such as cartilage.

Interstitial lamella: Bony lamella that lie between intact osteons.

Intramembranous ossification: Formation of osseous tissue within a mesenchymal membrane, which forms many flat bones in the fetus.

Mesenchyme: Primordial embryonic connective tissue derived from mesoderm, that forms all connective tissue.

Osseous tissue: Bone connective tissue with cells embedded in a mineralized matrix, which consists of about ⅓ organic ground substance and collagen fibers, and about ⅔ inorganic calcium salts (mostly hydroxyapatite).

Ossification: The formation of bone. Also called osteogenesis.

Osteoblast: A dividing bone-forming cell, derived from mesenchyme, that secretes an osseous matrix and fibers, becomes enclosed in a lacuna, then differentiates into an osteocyte.

Osteoclast: A giant multinucleated cell involved in the resorption and removal of osseous tissue, which becomes very active in the presence of parathyroid hormone (PTH).

Osteocyte: A cell of osseous tissue that occupies a lacuna and has cytoplasmic processes that extend into canaliculi and make contact by means of gap junctions with the processes of other osteocytes.

Osteogenic cell: Bone stem cell found in the inner layer of the periosteum that develops into osteoblasts.

Osteoid: Newly formed organic bone matrix before the addition of inorganic calcium salts.

Osteon: A series of concentric osseous lamellae that occur in compact bone, which surround a central canal with blood vessels, and contain osteocytes in lacunae (fluid-filled cavities). Also called haversian system.

Parathyroid Hormone (PTH): Hormone released by the parathyroid gland that raises blood calcium level and increases the activity of osteoclasts.

Perichondrium: Fibrous membrane covering the external surface around cartilage, that consists mostly of dense irregular connective tissue.

Periosteum: Thick membrane that covers the entire surface of a bone except its articular cartilage, and consists of two layers, an outer tough fibrous layer with blood vessels that nourish the bone, and a deeper osteogenic layer that can form new bone tissue.

Red bone marrow: Hematopoietic tissue that produces all of the blood cells; it is located in the spaces between the trabeculae of spongy bone.

Skeletal Cartilage: Cartilage surrounded by a perichondrium. Hyaline cartilage is the most abundant and forms the articular, costal, nasal, and respiratory cartilages. Fibrocartilage can withstand a great deal of pressure or stretch and is located in the intervertebral discs and the menisci of the knees. Elastic cartilage is very flexible and is located in the external ear (pinna or auricle), and in the epiglottis of the larynx.

Spongy bone: Lightweight bone tissue that makes up the interior of bones; consists of an irregular latticework of trabeculae containing many spaces filled with red bone marrow. Also called cancellous bone.

Wolff's Law: A bone grows and remodels in response to the forces that are placed upon it.