Skeletal System: Bone Structure and Function - Chapter 07B

This flashcard set covers the microscopic anatomy of compact and spongy bone, hyaline cartilage structure and growth, and the processes of intramembranous and endochondral ossification, as well as the zones of the epiphyseal plate.

Osteons (Haversian systems)

The small cylindrical structures that serve as the basic functional and structural unit of mature compact bone, appearing as a bull’s-eye target.

Central (Haversian) canal

A cylindrical channel at the center of an osteon, oriented parallel to it, through which blood vessels and nerves extend.

Concentric lamellae

Rings of bone connective tissue surrounding the central canal with collagen fibers oriented at $90$ degrees from previous and next lamellae to provide strength.

Osteocytes

Mature bone cells found in small spaces called lacunae between concentric lamellae that maintain the bone matrix.

Canaliculi

Tiny, interconnecting channels within bone connective tissue that house osteocyte projections and allow the exchange of nutrients, minerals, gases, and wastes.

Perforating (Volkmann) canals

Channels running perpendicular to central canals that connect central canals within different osteons.

Circumferential lamellae

Rings of bone running the entire circumference of the bone; categorized as external (internal to periosteum) or internal (internal to endosteum).

Interstitial lamellae

Components of compact bone found between osteons or representing partially resorbed osteons.

Trabeculae

An open lattice of narrow rods and plates of bone in spongy bone that forms a meshwork of crisscrossing bars to resist stresses.

Parallel lamellae

The bone matrix of spongy bone where osteocytes are located between adjacent layers.

Chondroblasts

Cells that produce the cartilage matrix in hyaline cartilage.

Chondrocytes

Chondroblasts that have been encased within the matrix, occupying small spaces called lacunae to maintain the matrix.

Perichondrium

A layer of dense irregular connective tissue that covers cartilage and helps maintain its shape.

Interstitial growth

Cartilage growth in length that begins during embryologic development and occurs within the internal regions of the cartilage.

Appositional growth

Cartilage growth in width that occurs on the outside surface of the cartilage.

Ossification (osteogenesis)

The formation and development of bone connective tissue, beginning in the embryo by the $8^{th}$ through $12^{th}$ weeks of development.

Intramembranous ossification

Also known as dermal ossification, this process involves bone growth within a thin layer of mesenchyme and produces flat bones of the skull, some facial bones, the mandible, and the central part of the clavicle.

Woven bone (primary bone)

Immature and poorly organized bone formed during the initial steps of intramembranous ossification.

Lamellar bone (secondary bone)

Mature bone that replaces woven bone, typically composed of two external layers of compact bone with a layer of spongy bone in between.

Endochondral ossification

Bone formation that begins with a hyaline cartilage model and produces most bones of the skeleton, including limbs, pelvis, and vertebrae.

Periosteal bone collar

A layer of osteoid secreted by osteoblasts around the calcified cartilage shaft during the development of a long bone.

Primary ossification center

The first major center of bone formation located in the diaphysis, with most formed by the $12^{th}$ week of development.

Secondary ossification centers

Centers of bone formation that form in the epiphyses as hyaline cartilage calcifies and degenerates.

Epiphyseal line

The internal thin line of compact bone that remains when the epiphyseal plate ossifies and bone reaches adult length, usually occurring between ages $10$ and $25$.

Zone of resting cartilage

The zone of the epiphyseal plate nearest to the epiphysis, composed of small chondrocytes that secure the epiphysis to the plate.

Zone of proliferating cartilage

The zone where chondrocytes undergo rapid mitotic division and align into longitudinal columns of flattened lacunae parallel to the diaphysis.

Zone of hypertrophic cartilage

The zone where chondrocytes cease dividing and greatly enlarge, causing the walls of the lacunae to become thin.

Zone of calcified cartilage

A zone composed of $2$ to $3$ layers of chondrocytes where minerals are deposited, which destroys the chondrocytes.

Zone of ossification

The zone where walls between lacunae break down and are invaded by capillaries and osteoprogenitor cells, allowing new bone matrix to be deposited.