Skeletal System
Key Terms
- articular cartilage
- thin layer of cartilage covering an epiphysis; reduces friction and acts as a shock absorber
- articulation
- where two bone surfaces meet
- bone
- hard, dense connective tissue that forms the structural elements of the skeleton
- canaliculi
- (singular = canaliculus) channels within the bone matrix that house one of an osteocyte’s many cytoplasmic extensions that it uses to communicate and receive nutrients
- cartilage
- semi-rigid connective tissue found on the skeleton in areas where flexibility and smooth surfaces support movement
- central canal
- longitudinal channel in the center of each osteon; contains blood vessels, nerves, and lymphatic vessels; also known as the Haversian canal
- closed reduction
- manual manipulation of a broken bone to set it into its natural position without surgery
- compact bone
- dense osseous tissue that can withstand compressive forces
- diaphysis
- tubular shaft that runs between the proximal and distal ends of a long bone
- diploë
- layer of spongy bone, that is sandwiched between two the layers of compact bone found in flat bones
- endochondral ossification
- process in which bone forms by replacing hyaline cartilage
- endosteum
- delicate membranous lining of a bone’s medullary cavity
- epiphyseal line
- completely ossified remnant of the epiphyseal plate
- epiphyseal plate
- (also, growth plate) sheet of hyaline cartilage in the metaphysis of an immature bone; replaced by bone tissue as the organ grows in length
- epiphysis
- wide section at each end of a long bone; filled with spongy bone and red marrow
- external callus
- collar of hyaline cartilage and bone that forms around the outside of a fracture
- flat bone
- thin and curved bone; serves as a point of attachment for muscles and protects internal organs
- fracture
- broken bone
- fracture hematoma
- blood clot that forms at the site of a broken bone
- hematopoiesis
- production of blood cells, which occurs in the red marrow of the bones
- hole
- opening or depression in a bone
- hypercalcemia
- condition characterized by abnormally high levels of calcium
- hypocalcemia
- condition characterized by abnormally low levels of calcium
- internal callus
- fibrocartilaginous matrix, in the endosteal region, between the two ends of a broken bone
- intramembranous ossification
- process by which bone forms directly from mesenchymal tissue
- irregular bone
- bone of complex shape; protects internal organs from compressive forces
- lacunae
- (singular = lacuna) spaces in a bone that house an osteocyte
- long bone
- cylinder-shaped bone that is longer than it is wide; functions as a lever
- medullary cavity
- hollow region of the diaphysis; filled with yellow marrow
- modeling
- process, during bone growth, by which bone is resorbed on one surface of a bone and deposited on another
- nutrient foramen
- small opening in the middle of the external surface of the diaphysis, through which an artery enters the bone to provide nourishment
- open reduction
- surgical exposure of a bone to reset a fracture
- orthopedist
- doctor who specializes in diagnosing and treating musculoskeletal disorders and injuries
- osseous tissue
- bone tissue; a hard, dense connective tissue that forms the structural elements of the skeleton
- ossification
- (also, osteogenesis) bone formation
- ossification center
- cluster of osteoblasts found in the early stages of intramembranous ossification
- osteoblast
- cell responsible for forming new bone
- osteoclast
- cell responsible for resorbing bone
- osteocyte
- primary cell in mature bone; responsible for maintaining the matrix
- osteogenic cell
- undifferentiated cell with high mitotic activity; the only bone cells that divide; they differentiate and develop into osteoblasts
- osteoid
- uncalcified bone matrix secreted by osteoblasts
- osteon
- (also, Haversian system) basic structural unit of compact bone; made of concentric layers of calcified matrix
- osteoporosis
- disease characterized by a decrease in bone mass; occurs when the rate of bone resorption exceeds the rate of bone formation, a common occurrence as the body ages
- perforating canal
- (also, Volkmann’s canal) channel that branches off from the central canal and houses vessels and nerves that extend to the periosteum and endosteum
- perichondrium
- membrane that covers cartilage
- periosteum
- fibrous membrane covering the outer surface of bone and continuous with ligaments
- primary ossification center
- region, deep in the periosteal collar, where bone development starts during endochondral ossification
- projection
- bone markings where part of the surface sticks out above the rest of the surface, where tendons and ligaments attach
- proliferative zone
- region of the epiphyseal plate that makes new chondrocytes to replace those that die at the diaphyseal end of the plate and contributes to longitudinal growth of the epiphyseal plate
- red marrow
- connective tissue in the interior cavity of a bone where hematopoiesis takes place
- remodeling
- process by which osteoclasts resorb old or damaged bone at the same time as and on the same surface where osteoblasts form new bone to replace that which is resorbed
- reserve zone
- region of the epiphyseal plate that anchors the plate to the osseous tissue of the epiphysis
- secondary ossification center
- region of bone development in the epiphyses
- sesamoid bone
- small, round bone embedded in a tendon; protects the tendon from compressive forces
- short bone
- cube-shaped bone that is approximately equal in length, width, and thickness; provides limited motion
- skeletal system
- organ system composed of bones and cartilage that provides for movement, support, and protection
- spongy bone
- (also, cancellous bone) trabeculated osseous tissue that supports shifts in weight distribution
- trabeculae
- (singular = trabecula) spikes or sections of the lattice-like matrix in spongy bone
- yellow marrow
- connective tissue in the interior cavity of a bone where fat is stored
- zone of calcified matrix
- region of the epiphyseal plate closest to the diaphyseal end; functions to connect the epiphyseal plate to the diaphysis
- zone of maturation and hypertrophy
- region of the epiphyseal plate where chondrocytes from the proliferative zone grow and mature and contribute to the longitudinal growth of the epiphyseal plate
