Bone Tissue and Skeletal System

Comprehensive vocabulary flashcards covering skeletal anatomy, bone histology, matrix composition, cartilage types, ossification pathways, homeostatic hormonal regulation, and fracture mechanics.

Compact Bone

Dense, cortical bone tissue that appears white, smooth, and solid, accounting for approximately $80\%$ of total bone mass.

Spongy Bone

Porous, cancellous, or trabecular bone tissue located internally to compact bone, constituting the remaining $20\%$ of total bone mass.

Hyaline Cartilage

A resilient, flexible connective tissue that covers articular surfaces of moveable joints, connects ribs to the sternum (costal), supports the nose, forms epiphyseal plates, and serves as the embryonic model for bone formation.

Fibrocartilage

A dense, weight-bearing cartilage found in regions subjected to heavy pressure and stretching, including intervertebral discs, the pubic symphysis, and knee menisci.

Ligament

A dense regular connective tissue band that anchors one bone to another.

Tendon

A dense regular connective tissue band that anchors skeletal muscle to bone.

Hematopoiesis

The biological process of blood cell production, occurring within red bone marrow.

Flat Bones

Bones with flat, thin, slightly curved surfaces that protect underlying soft tissue and provide extensive area for muscle attachment (e.g., cranial vault, scapulae, sternum, ribs).

Long Bones

The most common bone shape, characterized by an elongated cylindrical shaft (diaphysis) and two knobby ends (epiphyses); found in the upper and lower limbs.

Short Bones

Bones whose length is approximately equal to their width, such as carpals, tarsals, and sesamoid bones.

Sesamoid Bones

Small, flat, oval-shaped bones embedded within tendons to increase muscle leverage, such as the patella.

Irregular Bones

Bones featuring elaborate, complex shapes that do not fit into flat, long, or short categories, such as vertebrae, hip bones, and certain skull bones.

Diaphysis

The elongated, hollow cylindrical shaft of a long bone that provides weight support and leverage, containing an inner medullary cavity.

Epiphysis

The knobby, expanded end of a long bone consisting of an outer shell of compact bone and an inner core of spongy bone covered by articular cartilage.

Metaphysis

The region of mature bone situated between the diaphysis and epiphysis containing the epiphyseal (growth) plate.

Medullary Cavity

The central hollow chamber of the diaphysis, containing red bone marrow in children and yellow bone marrow in adults.

Periosteum

A double-layered sheath covering the external surface of bone, consisting of an outer dense irregular connective tissue fibrous layer and an inner cellular layer of osteogenic cells.

Perforating Fibers

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

Endosteum

An incomplete cellular layer lining the internal bone surfaces within the medullary cavity, composed of osteoprogenitor cells, osteoblasts, and osteoclasts.

Diploë

The internal layer of spongy bone found sandwiched between compact bone plates in the flat bones of the skull.

Red Bone Marrow

Hematopoietic soft connective tissue found in adult spongy bone and diploë, as well as the medullary cavities of children.

Yellow Bone Marrow

Adipose-filled connective tissue that replaces red bone marrow in the medullary cavity of adults, serving as a lipid energy reserve.

Osteoprogenitor Cells

Mitotically active stem cells located in the periosteum and endosteum that divide to give rise to osteoblasts.

Osteoblasts

Bone-forming cells that secrete new uncalcified bone matrix (osteoid) and become trapped within calcified matrix to differentiate into osteocytes.

Osteocytes

Mature bone cells residing inside lacunae that cannot produce new matrix, serving to maintain existing bone matrix and sense mechanical strain.

Osteoclasts

Large, multinucleated phagocytic cells derived from hematopoietic progenitors that break down and resorb bone matrix.

Resorption Lacuna

A shallow depression or pit on the bone surface where an osteoclast resides and dissolves bone matrix.

Osteoid

The organic component of bone matrix (approximately $\frac{1}{3}$ of the matrix), composed of collagen fibers and semi-solid ground substance that impart tensile strength.

Hydroxyapatite

Inorganic mineral salt crystals formed primarily by $\text{Ca}_3(\text{PO}_4)_2$ depositing along collagen fibers to provide rigidity and compressional strength.

Osteon

The basic microscopic cylindrical structural unit of compact bone running parallel to the bone's long axis, appearing like a bullseye in cross section.

Central Canal

The longitudinal central channel of an osteon containing blood vessels and nerve fibers supplying bone cells.

Concentric Lamellae

Rings of calcified matrix wrapped around the central canal, with collagen fibers oriented in alternating directions between adjacent rings to resist torsional forces.

Lacunae

Small cavities situated between adjacent lamellae that house mature osteocytes.

Canaliculi

Microscopic canals interconnecting lacunae and the central canal, housing cellular processes linked via gap junctions for nutrient transport and communication.

Perforating Canals

Volkmann canals running perpendicular to the bone's long axis that connect neurovascular structures between the periosteum, central canals, and medullary cavity.

Circumferential Lamellae

Rings of bone matrix that extend around the entire outer or inner circumference of compact bone, positioned directly beneath the periosteum or endosteum.

Interstitial Lamellae

Incomplete lamellar remnants lacking central canals, located between intact osteons as leftovers of resorbed osteons.

Trabeculae

A meshwork of narrow rods and plates of bone that align along lines of mechanical stress within spongy bone, lacking central canals and osteons.

Perichondrium

A dense irregular connective tissue sheath covering hyaline cartilage that houses blood vessels and stem cells.

Interstitial Growth (Cartilage)

Cartilage growth from within its internal regions, driven by chondrocyte mitosis within lacunae, synthesis of new matrix, and cell separation.

Appositional Growth (Cartilage)

Growth along the cartilage's outer edge, driven by stem cell division in the perichondrium and differentiation into matrix-secreting chondroblasts.

Zone of Resting Cartilage

The layer of the epiphyseal plate furthest from the medullary cavity, composed of mature non-dividing chondrocytes that secure the epiphysis to the plate.

Zone of Proliferating Cartilage

The epiphyseal plate zone where chondrocytes undergo rapid mitotic division and organize into vertical columns of flattened cells.

Zone of Hypertrophic Cartilage

The epiphyseal plate layer where cells cease dividing, enlarge, and begin resorbing surrounding cartilage matrix.

Zone of Calcified Cartilage

The zone where minerals deposit into the extracellular matrix around enlarged chondrocytes, leading to chondrocyte death.

Zone of Ossification

The epiphyseal plate zone nearest the diaphysis where blood capillaries invade and osteoblasts deposit new bone matrix over calcified matrix remnants.

Intramembranous Ossification

Bone formation directly within a fibrous mesenchymal membrane, generating flat bones such as those of the skull and clavicle.

Endochondral Ossification

Bone development that replaces a preexisting hyaline cartilage model, forming the majority of the skeleton including long bones, vertebrae, and the pelvis.

Primary Ossification Center

The initial area of bone formation during endochondral ossification, established within the diaphysis of the developing long bone.

Secondary Ossification Center

Sites of endochondral bone formation appearing in the epiphyses around the time of birth and childhood.

Wolff's Law

The principle stating that bones grow, remodel, and adapt structurally in direct response to the mechanical demands and stresses placed upon them.

Growth Hormone (GH)

Anterior pituitary hormone that stimulates the liver to produce somatomedins (IGFs), thereby enhancing chondrocyte division and skeletal growth.

Calcitriol

The active hormonal form of vitamin D converted in the liver and kidney that enhances intestinal absorption of $\text{Ca}^{2+}$ and $\text{PO}_4^{3-}$.

Parathyroid Hormone (PTH)

Hormone secreted by parathyroid glands in response to low plasma $\text{Ca}^{2+}$; acts on bone to stimulate osteoclasts, the kidney to retain calcium, and the intestine via calcitriol activation.

Calcitonin

Hormone released by thyroid C cells in response to elevated plasma $\text{Ca}^{2+}$ that inhibits osteoclasts and promotes renal calcium excretion.

Colles Fracture

A fracture of the distal end of the lateral forearm bone (radius) that produces a characteristic dinner fork deformity.

Comminuted Fracture

A bone fracture in which the bone is splintered into several small fragments between the main broken segments.

Greenstick Fracture

A partial fracture where one side of the bone breaks while the opposite side bends, typical in children.

Pott Fracture

A fracture involving the distal ends of both the tibia and fibula at the ankle.

Pathologic Fracture

A fracture caused by normal mechanical stresses occurring in a bone weakened by a disease process such as osteoporosis or cancer.

Fracture Hematoma

A localized clotted blood mass that forms immediately after fracture as a result of torn blood vessels in the bone.

Fibrocartilaginous (Soft) Callus

A temporary repair tissue of collagen and fibrocartilage formed during the second stage of bone fracture healing that splints the fractured bone fragments.

Hard (Bony) Callus

A rigid primary bone structure formed when osteoblasts replace the soft fibrocartilaginous callus with trabecular bone during fracture healing.