A&P Skeletal System Definitions

hematopoiesis

production of blood cells, which occurs in the red marrow of the bones

endosteum

delicate membranous lining of a bone's medullary cavity

compact bone

dense osseous tissue that can withstand compressive forces

osteoclast

cell responsible for resorbing bone

ossification center

cluster of osteoblasts found in the early stages of intramembranous ossification

osteogenic cell

undifferentiated cell with high mitotic activity; the only bone cells that divide; they differentiate and develop into osteoblasts

osteon

(also, Haversian system) basic structural unit of compact bone; made of concentric layers of calcified matrix

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

spongy bone

(also, cancellous bone) trabeculated osseous tissue that supports shifts in weight distribution

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

ossification

(also, osteogenesis) bone formation

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

lacunae

(singular = lacuna) spaces in a bone that house an osteocyte

trabeculae

(singular = trabecula) spikes or sections of the lattice-like matrix in spongy bone

fracture hematoma

blood clot that forms at the site of a broken bone

projection

bone markings where part of the surface sticks out above the rest of the surface, where tendons and ligaments attach

irregular bone

bone of complex shape; protects internal organs from compressive forces

osseous tissue

bone tissue; a hard, dense connective tissue that forms the structural elements of the skeleton

fracture

broken bone

osteoblast

cell responsible for forming new bone

external callus

collar of hyaline cartilage and bone that forms around the outside of a fracture

epiphyseal line

completely ossified remnant of the epiphyseal plate

hypercalcemia

condition characterized by abnormally high levels of calcium

hypocalcemia

condition characterized by abnormally low levels of calcium

yellow marrow

connective tissue in the interior cavity of a bone where fat is stored

red marrow

connective tissue in the interior cavity of a bone where hematopoiesis takes place

short bone

cube-shaped bone that is approximately equal in length, width, and thickness; provides limited motion

long bone

cylinder-shaped bone that is longer than it is wide; functions as a lever

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

orthopedist

doctor who specializes in diagnosing and treating musculoskeletal disorders and injuries

internal callus

fibrocartilaginous matrix, in the endosteal region, between the two ends of a broken bone

periosteum

fibrous membrane covering the outer surface of bone and continuous with ligaments

bone

hard, dense connective tissue that forms the structural elements of the skeleton

medullary cavity

hollow region of the diaphysis; filled with yellow marrow

diploë

layer of spongy bone, that is sandwiched between two the layers of compact bone found in flat bones

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

perichondrium

membrane that covers cartilage

hole

opening or depression in a bone

skeletal system

organ system composed of bones and cartilage that provides for movement, support, and protection

osteocyte

primary cell in mature bone; responsible for maintaining the matrix

intramembranous ossification

process by which bone forms directly from mesenchymal tissue

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

endochondral ossification

process in which bone forms by replacing hyaline cartilage

modeling

process, during bone growth, by which bone is resorbed on one surface of a bone and deposited on another

secondary ossification center

region of bone development in the epiphyses

zone of calcified matrix

region of the epiphyseal plate closest to the diaphyseal end; functions to connect the epiphyseal plate to the diaphysis

reserve zone

region of the epiphyseal plate that anchors the plate to the osseous tissue of the epiphysis

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

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

primary ossification center

region, deep in the periosteal collar, where bone development starts during endochondral ossification

cartilage

semi-rigid connective tissue found on the skeleton in areas where flexibility and smooth surfaces support movement

nutrient foramen

small opening in the middle of the external surface of the diaphysis, through which an artery enters the bone to provide nourishment

sesamoid bone

small, round bone embedded in a tendon; protects the tendon from compressive forces

open reduction

surgical exposure of a bone to reset a fracture

flat bone

thin and curved bone; serves as a point of attachment for muscles and protects internal organs

articular cartilage

thin layer of cartilage covering an epiphysis; reduces friction and acts as a shock absorber

diaphysis

tubular shaft that runs between the proximal and distal ends of a long bone

osteoid

uncalcified bone matrix secreted by osteoblasts

articulation

where two bone surfaces meet

epiphysis

wide section at each end of a long bone; filled with spongy bone and red marrow