Module 6, Bone & Bone Structure

Axial Skeleton

The central, vertical axis of the skeleton, including the skull, vertebrae, and thoracic cage.

Appendicular Skeleton

The bones of the upper and lower appendages and their girdles which attach them to the axial skeleton.

Flat Bones

A thin bone with two parallel sides.

Sutural Bones

A small bone that forms within a suture in the skull.

Long Bones

A bone that is longer than it is wide.

Irregular Bones

A bone with a complex shape.

Sesamoid Bones

A bone that forms within a tendon and is shaped like a sesame seed.

Short Bones

A bone that is approximately cube-shaped.

Epiphysis

The expanded proximal and distal end of a long bone; filled with spongy bone and red bone marrow.

Diaphysis

The hollow shaft of a long bone, made from mostly compact bone.

Metaphysis

The neck region of a long bone between the epiphysis and diaphysis.

Medullary Cavity

The hollow space within the diaphysis of a long bone that is filled with yellow bone marrow.

Compact Bone

Dense osseous tissue formed by tightly-packed osteons.

Spongy Bone

Osseous tissue formed by loosely packed trabeculae.

Periosteum

A fibrous membrane that wraps around the outside of a bone and is continuous with ligaments.

Endosteum

A thin membrane lining the medullary cavity.

Growth Plate

A sheet of hyaline cartilage within the metaphysis of a long bone that allows for a bone to grow in length; epiphyseal plate.

Osteogenic Cell

A stem cell in osseous tissue that can divide to generate osteoblasts and osteoclasts.

Osteoblast

An immature bone cell that produces new bone tissue (calcified osteoid).

Osteocyte

A mature osteoblast that has surrounded itself with bone tissue and serves to maintain bone tissue.

Osteoclast

A bone cell that breaks down bone tissue.

Osteogenesis / Ossification

The process of bone formation.

Osteoid

Non-calcified bone matrix produced by osteoblasts.

Osteolysis

The process of bone tissue breaking down.

Hydroxyapatite

The primary calcium-based chemical found within developing bone.

Osteon

The repetitive unit of compact bone formed by concentric layers of calcified bone tissue; haversian canals.

Concentric Lamella

A ring-shaped layer of calcified bone tissue around the central canal of an osteon.

Central Canal

The central channel within an osteon which contains blood vessels, lymphatic vessels, and nerves.

Lacunae

A space within osseous or cartilage tissue where an osteocyte and chondrocyte are respectively found.

Circumferential Lamella

A layer of calcified bone tissue around the outside of the diaphysis of a long bone.

Interstitial Lamella

A layer of calcified bone tissue located between osteons in compact bone; a remnant of an older osteon.

Canaliculus

A tiny channel extending out from lacuna that contains extensions of the osteocyte membrane and is used to transport nutrients and remove waste.

Perforating Canals

A channel that branches off the primary lacuna to bring in nutrient Volksmann channel.

Spongy Bone

Osseous tissue comprised of trabeculae organized in randomized direction to support shifts in pressure; cancellous bone.

Trabecula

A spike or section of the lattice-like matrix in spongy bone, similar to an individual osteon from compact bone without the central canal.

Appositional Growth

Growth in diameter.

Interstitial Growth

Growth in length.

Osteoclastic Crypts

Depressions within bone matrix where many osteoclasts are located and bone is being resorbed.

Endochondral Ossification

The process by which osseous tissue is formed by replacing existing hyaline cartilage.

Primary Ossification Center

A region in the center of a hyaline cartilage bone model where endochondral ossification forms the diaphysis.

Secondary Ossification Center

A region in the ends of a hyaline cartilage bone model where endochondral ossification forms the epiphysis.

Epiphyseal Plate

A sheet of hyaline cartilage within the metaphysis of a long bone that allows for a bone to grow in length; growth plate.

Epiphyseal Line

The ossified remnant of the epiphyseal plate.

Epiphyseal Closure

The process by which the hyaline cartilage of the epiphyseal plate is converted to osseous tissue, forming the epiphyseal line.

Articular Cartilage

A thin layer of hyaline cartilage covering the epiphysis that reduces friction within a joint.

Fracture

Broken bone.

Closed / Simple Fracture

A fracture in which the bone has not broken the skin.

Open / Compound Fracture

A fracture in which the bone has broken through the skin.

Transverse Fracture

A fracture in which the bone has broken perpendicular to the long axis of the bone.

Spiral Fracture

A fracture in which the bone has broken at an oblique angle due to a twisting force.

Displaced Fracture

A fracture in which the two ends of bone are separated from one another.

Compression Fracture

A fracture in which the bone (typically a vertebra) has collapsed due to pressure along its vertical axis.

Greenstick Fracture

A partial fracture seen in bones that have not fully ossified in which one part of the bone has broken.

Comminuted Fracture

A fracture in which the bone has broken into multiple small pieces between two larger segments.

Epiphyseal Fracture

A fracture along the epiphyseal plate of a long bone; growth plate fracture.

Fracture Hematoma

A blood clot that forms at the site of a broken bone.

Internal Callus

A temporary matrix of fibrocartilage and spongy bone that forms between the two ends of broken bone.

External Callus

A temporary matrix of hyaline cartilage that forms on the outside of a broken bone.

Osteoporosis

A clinically significant decrease in bone density which is related to an increased risk of fractures.

Osteopenia

A condition characterized by a lower than normal bone density which can progress to osteoporosis.