Skeletal System

Comprehensive vocabulary flashcards covering skeletal system functions, bone classifications, surface markings, microscopic and gross anatomy, bone cells, ossification processes, repair mechanisms, fracture classifications, and clinical bone pathologies.

Long Bone

A bone that is longer than it is wide, slender, and functions to support weight and facilitate movement (e.g., femur and humerus).

Short Bone

A small, box-like or box-shaped bone (e.g., carpal bones in the wrist and tarsal bones in the ankle).

Flat Bone

A thin, broad bone with thin parallel surfaces that provides protection for internal organs or extensive surface area for muscle attachment (e.g., cranial bones, sternum, ribs, and scapula).

Irregular Bone

A bone featuring a complex shape with short, flat, or notched surfaces that does not fit into other morphological classifications (e.g., vertebrae and pelvic bones).

Sutural Bone

A small, flat, irregularly shaped extra bone found within skull sutures; its number varies among individuals and is excluded from the standard $206$-bone skeletal count.

Sesamoid Bone

A small, round, and flat bone that develops within tendons adjacent to joints (e.g., patella).

Head

A rounded, expanded articular end of a bone.

Neck

A narrow region connecting the head of a bone to its shaft.

Condyle

A smooth, rounded articular projection on a bone.

Epicondyle

A bony projection located above a condyle.

Trochanter

A large, prominent projection found exclusively on the femur.

Tuberosity

A large, roughened projection on a bone designed for muscle or ligament attachment.

Tubercle

A small, rounded projection on a bone.

Crest

A prominent ridge along the edge or surface of a bone.

Spine

A sharp, slender projection on a bone.

Process

Any bony prominence or projection.

Facet

A small, smooth, flat articular surface on a bone.

Fossa

A shallow depression on the surface of a bone.

Foramen

A rounded opening or hole through a bone that permits the passage of nerves or blood vessels.

Meatus

A canal-like passageway through a bone.

Sulcus

A groove on a bone surface.

Compact Bone

Dense, solid cortical bone tissue organized into osteons that forms the protective outer wall of bones and resists mechanical stress.

Spongy Bone

Cancellous bone tissue characterized by an open, porous network of trabeculae that houses bone marrow, lightens the skeleton, and withstands multi-directional stresses.

Trabeculae

The branching struts, bands, and arches of bone matrix forming the internal framework of spongy bone.

Diaphysis

The extended tubular shaft of a long bone composed primarily of compact bone surrounding the medullary cavity.

Epiphysis

The expanded end of a long bone, consisting predominantly of spongy bone enveloped by a thin shell of compact bone.

Metaphysis

The transitional growth zone located between the diaphysis and epiphysis of a developing long bone.

Epiphyseal Plate

A hyaline cartilage growth plate situated in the metaphysis responsible for longitudinal bone growth; appears as a gap on radiographs.

Epiphyseal Line

The bony remnant of the epiphyseal plate formed when longitudinal growth terminates and cartilage is replaced by bone; appears as a distinct thin line on radiographs.

Medullary Cavity

The hollow central space within the diaphysis of a long bone lined by endosteum and filled with marrow.

Articular Cartilage

A layer of hyaline cartilage covering the articular ends of bones in synovial joints that lacks a periosteum.

Periosteum

A specialized connective tissue sheath covering the outer bone surface consisting of an outer fibrous layer and an inner cellular layer containing osteogenic cells and osteoblasts.

Endosteum

A thin, incomplete internal membrane lining the medullary cavity, trabecular surfaces, and central canals, containing osteoblasts, osteocytes, osteoclasts, and osteoprogenitor cells.

Osteon

The primary structural and functional unit of mature compact bone, consisting of concentric lamellae surrounding a central canal containing blood vessels.

Central Canal

A longitudinal channel running through the center of an osteon (Haversian canal) that houses blood vessels and nerves.

Concentric Lamellae

Circular layers of mineralized bone matrix arranged concentrically around the central canal of an osteon.

Circumferential Lamellae

Bony layers that extend around the inner and outer circumferences of the entire bone shaft.

Interstitial Lamellae

Remnants of older, remodeled osteons that fill the irregular spaces situated between active osteons.

Lacuna

A small chamber or pocket within the calcified matrix that encloses a single osteocyte.

Canaliculi

Narrow, microscopic passageways that radiate across the bone matrix, connecting lacunae to each other and to the central canal for cellular exchange and communication.

Osteoprogenitor Cell

A mesenchymal stem cell found within the inner periosteal layer and endosteum that divides and differentiates into osteoblasts.

Osteoblast

A bone-building cell that synthesizes and deposits new organic bone matrix (osteoid) and matures into an osteocyte once encased.

Osteocyte

A mature bone cell residing inside a lacuna that maintains, breaks down, and re-deposits bone matrix immediately surrounding itself.

Osteoclast

A large, multinucleated bone-resorbing cell derived from immune system precursors that secretes acids and enzymes to dissolve bone matrix.

Osteoid

The organic, uncalcified extracellular matrix secreted by osteoblasts prior to mineral deposition.

Red Bone Marrow

A specialized hematopoietic tissue found in spongy bone spaces of flat bones and selected long bones that produces red blood cells, white blood cells, and platelets.

Yellow Bone Marrow

A lipid-rich marrow residing in the medullary cavities of adult long bones that functions as an energy reserve.

Endochondral Ossification

The developmental process of bone formation wherein an initial hyaline cartilage model is progressively replaced by mineralized bone tissue.

Primary Ossification Center

The first central site of bone formation within the diaphysis of a cartilage model during endochondral ossification.

Secondary Ossification Center

A site of bone formation that develops within the epiphyses of long bones during endochondral ossification.

Intramembranous Ossification

The direct development of bone from embryonic mesenchymal or fibrous connective tissue without the formation of an intermediate cartilage model (forming cranial flat bones, mandible, and clavicle).

Bone Remodeling

The dynamic, lifelong physiological process whereby existing mineralized matrix is resorbed by osteoclasts and replaced by osteoblasts in response to hormonal signals and mechanical stress.

Fracture Hematoma

A localized blood clot that forms immediately around torn vessels following a bone fracture to arrest hemorrhage and trigger the repair response.

External Callus

A stabilizing mass of cartilage and bone that develops around the external surface of a bone break during fracture repair.

Internal Callus

A bridge of spongy bone produced by endosteal cells inside the medullary cavity that reunites the fractured internal ends.

Bone Fracture Types

Categories of bone breaks defined by structural pattern, alignment, and mechanism of mechanical failure.

Transverse Fracture

A fracture that creates a straight break running perpendicular across the long axis of the bone.

Displaced Fracture

A bone break wherein the fractured ends are separated or shifted out of normal anatomical alignment.

Compression Fracture

A fracture characterized by crushing or compaction of the bone structure, typically occurring under vertical loading.

Spiral Fracture

A bone break that twists spirally along the shaft, resulting from torsional or rotational forces.

Epiphyseal Fracture

A fracture occurring near or directly across the epiphyseal cartilage plate.

Comminuted Fracture

A fracture in which the affected bone shatters into three or more fragments.

Greenstick Fracture

An incomplete fracture where one cortex of the bone cracks while the opposing side bends; primarily observed in juvenile skeletons.

Colles' Fracture

A fracture of the distal radius near the wrist, frequently sustained by attempting to break a fall.

Pott's Fracture

A fracture involving the ankle region, classically affecting the distal fibula.

Osteopenia

A clinical state characterized by lower-than-normal bone mineral density that commonly accompanies aging.

Osteoporosis

A severe skeletal disorder marked by significant loss of bone mass, thinning of trabeculae, enlarged inter-trabecular spaces, and elevated susceptibility to fractures.