Bones and Skeletal System

A complete set of vocabulary flashcards covering skeletal tissues, cartilage types, bone cells, histology, endochondral ossification, fractures, and bone pathologies based on A&P I Lesson 6.

Perichondrium

A layer of dense connective tissue that surrounds skeletal cartilage, which lacks its own blood vessels and nerves.

Chondrocytes

Cartilage-producing cells that reside within small spaces in the matrix called lacunae.

Hyaline cartilage

The most abundant type of skeletal cartilage, located at the tip of the nose, respiratory tract, costal cartilages, and the articular ends of long bones.

Elastic cartilage

A flexible type of cartilage found exclusively in the pinnae of the external ears and the epiglottis.

Fibrocartilage

A highly compressible cartilage with high tensile strength, located in the intervertebral discs, pubic symphysis, and menisci of the knee.

Articular cartilage

Hyaline cartilage covering the ends of long bones at joint surfaces to cushion bone-on-bone contact.

Osteoid

The organic component of bone matrix making up $35\%$ of mass, consisting of cells and collagen fibers that contribute to bone structure and flexibility.

Inorganic bone components

Mineralized matrix elements comprising $65\%$ of bone mass, primarily calcium phosphates, responsible for bone hardness and resistance to compression.

Osteogenic cells

Mitotically active stem cells located in the periosteum and endosteum that differentiate into osteoblasts.

Osteoblasts

Young matrix-synthesizing cells responsible for bone growth and matrix deposition.

Osteocytes

Mature bone cells that become completely surrounded by matrix to monitor and maintain the mineralized bone matrix.

Osteoclasts

Large, multinucleated bone-resorbing cells derived from white blood cell lineage that secrete acids and hydrolytic enzymes to break down bone and release $Ca^{2+}$ into the bloodstream.

Compact bone

The dense, solid outer layer of bone tissue composed of structural units called osteons.

Spongy bone

The internal layer of bone having a honeycomb appearance made of trabeculae and containing red bone marrow.

Trabeculae

Small needle-like or flat spicules of bone that form the meshwork of spongy (cancellous) bone.

Axial skeleton

The division of the skeleton that forms the long axis of the body, comprising the skull, vertebral column, and rib cage.

Appendicular skeleton

The division of the skeleton consisting of the upper and lower limbs and their supporting girdles (scapulae, clavicles, and hip bones).

Long bones

Bones that are longer than they are wide, such as the humerus, femur, and tibia.

Short bones

Roughly cube-shaped bones, such as the trapezoid and other carpals and tarsals.

Flat bones

Thin, flattened, and usually curved bones, including the sternum, ribs, and cranial bones of the skull.

Irregular bones

Bones with complex, irregular shapes that do not fit long, short, or flat classifications, such as vertebrae.

Diaphysis

The tubular shaft running along the longitudinal axis of a long bone, composed of a collar of compact bone enclosing a medullary cavity.

Epiphysis

The expanded proximal or distal end of a long bone, covered externally by articular cartilage and internally containing spongy bone.

Periosteum

A double-layered membrane covering the outer surface of bone, consisting of an outer dense irregular CT fibrous layer and an inner osteogenic layer containing osteogenic cells, osteoblasts, and osteoclasts.

Endosteum

A delicate connective tissue membrane lining internal bone surfaces, such as the medullary cavity, canals, and trabeculae.

Osteon

The elongated cylindrical structural and functional unit of compact bone, also known as the Haversian system.

Lamellae

Concentric rings or tubes of calcified bone matrix surrounding the central canal within an osteon.

Lacunae

Small spaces located between adjacent lamellae that house mature osteocytes.

Canaliculi

Hair-like canals connecting lacunae to each other and to the central canal, facilitating nutrient exchange and communication between osteocytes.

Central canal

A channel located at the center of an osteon containing blood vessels and nerves that run longitudinally through bone.

Intramembranous ossification

The developmental process by which bone forms directly from a fibrous membrane, giving rise to cranial bones of the skull and the clavicles.

Endochondral ossification

The developmental process by which bone forms by progressively replacing a preexisting hyaline cartilage model, occurring in all bones below the skull except the clavicles.

Primary ossification center

The initial region in the center of the hyaline cartilage diaphysis where bone tissue begins replacing cartilage during fetal development.

Secondary ossification center

Regions appearing in the epiphyses around birth where cartilage is replaced by spongy bone without forming a medullary cavity.

Epiphyseal plate

A band of hyaline cartilage located between the diaphysis and epiphysis that permits longitudinal bone growth during childhood and adolescence.

Proliferation zone

The cartilage zone of the epiphyseal plate where chondroblasts divide rapidly and push the epiphysis away from the diaphysis, lengthening the bone.

Hypertrophic zone

The region in the epiphyseal plate where older chondrocytes enlarge and signal the surrounding matrix to calcify.

Calcification zone

The zone where the cartilage matrix calcifies and chondrocytes die, leaving calcified cartilage spicules that are not yet true bone.

Ossification zone

The zone where osteoclasts digest calcified cartilage and osteoblasts replace it with actual bone tissue in the form of bone trabeculae.

Appositional growth

The growth of a bone in diameter or thickness, driven by osteoblasts depositing bone under the periosteum while osteoclasts resorb bone along the endosteum.

Wolff's Law

The anatomical principle stating that bone grows or remodels in response to the physical stresses and mechanical demands placed upon it.

Pituitary dwarfism

A childhood growth disorder characterized by abnormally short stature, caused by an inadequate secretion of Growth Hormone (hypopituitarism).

Gigantism

A growth condition caused by excessive production of Growth Hormone during childhood before the closure of epiphyseal plates.

Hematoma

A localized mass of clotted blood that forms at the site of a fracture due to severed blood vessels, marking the initial stage of bone repair.

Fibrocartilaginous callus

A temporary splint composed of collagen fibers and cartilage that spans the fracture site during the second stage of bone repair.

Bony callus

A rigid mass of spongy bone trabeculae that replaces the fibrocartilaginous callus during the third stage of fracture healing.

Comminuted fracture

A fracture pattern where the bone shatters or splinters into three or more fragments.

Greenstick fracture

An incomplete fracture where one side of the bone shaft breaks and the opposite side bends, commonly observed in children due to high organic matrix content.

Compound fracture

An open fracture in which the ends of the fractured bone break through the skin, carrying a high risk of bacterial infection.

Simple fracture

A closed fracture where the broken bone remains enclosed within the soft tissues and does not penetrate through the skin.

Osteoporosis

A metabolic bone disorder wherein osteoclast resorption exceeds osteoblast deposition, producing porous, fragile bones and elevated fracture risk, commonly triggered by estrogen decline in postmenopausal women.

Rickets

A childhood disease caused by a deficiency in calcium or vitamin D, leading to soft, unmineralized bones and weight-bearing skeletal deformities such as bowed legs.

Osteomalacia

A condition in adults caused by insufficient calcium or vitamin D, leading to poor bone mineralization, soft bones, and pain upon weight-bearing.