Bones and Axial Skeleton: Bone Anatomy, Histology, and Mechanics

Vocabulary practice flashcards covering skeletal tissues, long bone gross anatomy, microscopic structures of compact and spongy bone, bone remodeling cells, matrix composition, and biomechanical stress adaptations.

Osseous Tissue

Bone tissue

Red Marrow

Soft tissue located inside bone cavities that serves as the site of red blood cell production and houses hematopoietic stem cells.

Yellow Marrow

Fatty marrow tissue located in bone cavities consisting primarily of blood vessels and adipocytes that functions in fat storage.

Periosteum

The outermost fibrous connective tissue layer enveloping the external surface of a bone.

Perforating Fibers

Collagen fibers that firmly anchor the periosteum to the underlying compact bone matrix.

Endosteum

The delicate connective tissue membrane lining the inner surfaces and internal cavities of bone tissue.

Medullary Cavity

The hollow internal chamber within the diaphysis of a long bone where bone marrow is stored.

Epiphyseal Lines

The visible bony remnants of the growth plates (epiphyseal plates) remaining after long bone longitudinal growth ceases.

Long Bones

A shape classification defining bones that are longer in dimension than they are wide.

Short Bones

A shape classification defining bones that are approximately equal in length and width, giving them a cube-shaped appearance.

Flat Bones

A shape classification designating bones that are thin, broad, and frequently curved.

Sesamoid Bones

Specialized, small, flat, and oval-shaped bones that develop embedded directly within tendons.

Irregular Bones

Bones with complex structures that do not fit into the long, short, flat, or sesamoid shape categories.

Osteogenic Cells

Bone stem and progenitor cells that undergo division and differentiate into osteoblasts.

Osteoblasts

Bone-building cells responsible for forming bone matrix and mineralizing the organic components of the matrix.

Osteocytes

Mature bone cells entrapped in lacunae that function to maintain the surrounding bone tissue.

Osteoclasts

Large, specialized multinucleated cells located in the endosteum that demineralize and reabsorb bone by secreting lysosomal enzymes and metabolic acids and phagocytizing bone matrix.

Inorganic Matrix

The component of bone extracellular matrix comprising approximately $65\%$ of its weight, composed of hydroxyapatite mineral salts ($Ca^{2+}$ and $P$) that enable bone to resist compressive forces.

Organic Matrix

The component of bone extracellular matrix comprising approximately $35\%$ of its weight, consisting of collagen protein fibers, proteoglycans, glycosaminoglycans, and glycoproteins that resist bending, stretching, and tensile forces.

Osteon

The basic, microscopic cylindrical structural unit of compact bone, also known as a Haversian system, composed of concentric lamellae surrounding a central canal.

Central Canal

A longitudinal channel running through the core of an osteon containing nerves, capillaries, and venules.

Perforating Canals

Horizontal canals, also known as Volkmann's canals, that run perpendicular to osteons to connect central canals and transmit neurovascular bundles from the periosteum.

Canaliculi

Microscopic passageways permeating the bone matrix that interconnect adjacent lacunae, allowing transport of cellular secretions and communication between osteocytes.

Trabeculae

A meshwork of branching bony beams found in spongy (cancellous) bone lacking central canals, arranged along lines of stress to provide a protective framework for marrow.

Endochondral Ossification

The developmental process by which long bones grow in length through the gradual calcification and replacement of a hyaline cartilage scaffold with osseous tissue.

Bone Collar

A cuff of osteoid deposited by osteoblasts around the perimeter of the hyaline cartilage diaphysis early in endochondral ossification.

Proliferating Zone

The region of the epiphyseal plate where chondrocytes actively divide by mitosis, leaving daughter cells toward the epiphysis while pushing older cells toward the diaphysis.

Hypertrophic Zone

The region of the epiphyseal growth plate where older chondrocytes enlarge significantly and undergo apoptosis.

Calcification Zone

The zone in growing long bones where the extracellular cartilage matrix surrounding dying chondrocytes calcifies, blood vessels invade, and osteoblasts begin laying down bone matrix.

Appositional Growth

The process by which bones increase in diameter and wall thickness through osteoblasts secreting matrix onto the external bone surface while osteoclasts resorb bone along the internal surface.

Yield Point

The threshold point on a bone's stress-strain curve that separates the recoverable elastic deformation region from the permanent plastic deformation region.

Skeletal Demineralization

The loss of bone mineral density resulting from reduced mechanical loading, evidenced in spaceflights such as Gemini 4 ($4\text{ days}$, $-12\%$ demineralization) and Gemini 5 ($8\text{ days}$, $-20\%$ demineralization).