Bone Tissue and Skeletal System Physiology

Essential vocabulary flashcards covering skeletal system structure, histology, osteogenesis, growth mechanisms, calcium regulation, fracture types, and bone pathologies.

Hemopoiesis

The process of blood cell production that occurs in the red bone marrow of certain bones.

Bone Extracellular Matrix

The intercellular substance surrounding bone cells, composed of approximately $15\%$ water, $30\%$ collagen fibers, and $55\%$ crystallized mineral salts.

Osteoprogenitor Cells

Unspecialized bone stem cells derived from mesenchyme that undergo cell division to develop into osteoblasts.

Osteoblasts

Bone-building cells that synthesize and secrete organic extracellular matrix components, including collagen, and initiate calcification.

Osteocytes

Mature bone cells that maintain daily bone tissue metabolism, such as the exchange of nutrients and wastes with the blood.

Osteoclasts

Huge, multinucleated cells derived from white blood cell lineages with a ruffled border that function in bone resorption by breaking down extracellular matrix.

Compact Bone

The dense, strong type of bone tissue composed of repeating osteons that provides protection, support, and resists stresses produced by weight and movement.

Spongy Bone

A lightweight type of bone tissue lacking true osteons, arranged in an irregular latticework of trabeculae that support tissue and house red bone marrow.

Diaphysis

The tubular shaft or body that forms the long, main portion of a long bone.

Epiphyses

The proximal and distal extremities or ends of a long bone.

Metaphysis

The region of a mature long bone between the diaphysis and epiphysis that contains the epiphyseal plate (or epiphyseal line in adults).

Endosteum

A thin internal membrane lining the medullary cavity and covering the trabeculae of spongy bone.

Periosteum

A tough, double-layered connective tissue sheath covering the outer bone surface where it is not covered by articular cartilage.

Diploe

The internal layer of spongy (trabecular) bone sandwiched between layers of compact bone in short, irregular, and flat bones.

Osteon

The fundamental microscopic structural and functional unit of adult compact bone.

Central (Haversian) Canal

A longitudinal channel running through the core of an osteon containing blood vessels and nerve fibers.

Perforating Canals

Endosteum-lined channels oriented at right angles to central canals that connect nerves and blood vessels of the periosteum, medullary cavity, and central canals.

Lacunae

Small spaces situated between concentric lamellae that contain osteocytes.

Canaliculi

Microscopic, hairlike channels radiating from lacunae that connect adjacent lacunae and central canals, allowing nutrient transport and communication.

Trabeculae

Lamellar bone arranged in an irregular, branching meshwork of thin columns or plates in spongy bone.

Intramembranous Ossification

The embryonic process in which bone forms directly on or within fibrous connective tissue membranes, generating flat bones such as skull bones and the mandible.

Endochondral Ossification

The replacement of a temporary hyaline cartilage model by bone tissue, responsible for developing most bones of the skeleton.

Primary Ossification Center

The initial site of endochondral ossification located in the diaphysis, where bone tissue first replaces most of the cartilage model.

Secondary Ossification Center

The ossification sites that develop in the epiphyses of long bones around the time of birth, where spongy bone is deposited without a medullary cavity.

Epiphyseal Plate

A layer of hyaline cartilage within the metaphysis of growing long bones responsible for post-natal lengthwise (interstitial) elongation.

Interstitial Growth

Growth in bone length driven by chondrocyte division on the epiphyseal side of the growth plate and bone replacement on the diaphyseal side.

Appositional Growth

Growth in bone diameter/thickness occurring as osteoblasts beneath the periosteum deposit new lamellae while osteoclasts widen the medullary cavity from within.

Bone Remodeling

The ongoing replacement of old bone tissue by new bone tissue, comprising bone resorption by osteoclasts and bone deposition by osteoblasts.

Wolff's Law

The physiological principle stating that bone architecture and density adapt and remodel directly in response to the mechanical forces and stresses applied to them.

Parathyroid Hormone (PTH)

A hormone secreted by the parathyroid glands that increases blood $Ca^{2+}$ concentration by stimulating osteoclast activity, promoting renal calcium reabsorption, and activating calcitriol.

Calcitonin (CT)

A hormone secreted by parafollicular cells of the thyroid gland that inhibits osteoclast activity, promotes bone deposition, and lowers blood $Ca^{2+}$ concentration.

Calcitriol

The active hormonal form of vitamin D produced by the kidneys that increases absorption of calcium and phosphate from the gastrointestinal tract into the blood.

Open (Compound) Fracture

A bone fracture in which the broken ends of the bone protrude through the skin.

Comminuted Fracture

A fracture in which the bone splinters, crumbles, or shatters into small fragments at the site of impact.

Greenstick Fracture

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

Impacted Fracture

A fracture where one end of the broken bone is forcefully driven into the interior of the other fragment.

Pott Fracture

A fracture of the distal end of the lateral leg bone (fibula), with serious injury to the distal tibial articulation.

Colles Fracture

A fracture of the distal end of the lateral forearm bone (radius) in which the distal fragment is displaced posteriorly.

Fracture Hematoma

A mass of clotted blood that forms around the site of a bone break during the initial reactive phase of fracture repair.

Fibrocartilaginous Callus

A mass of repair tissue consisting of collagen fibers and cartilage that bridges the broken ends of a bone during the reparative phase.

Osteomalacia

A condition in adults characterized by poorly mineralized, soft, and weak bones with pain upon weight-bearing, caused by inadequate calcium salts or vitamin D.

Rickets

A childhood disorder caused by vitamin D or calcium deficiency where bone ends become enlarged, abnormally long, and poorly mineralized, leading to characteristic bowed legs and skeletal deformities.

Osteoporosis

A group of diseases in which bone resorption outpaces bone deposition, resulting in diminished bone mass, porous trabeculae, and a heightened susceptibility to fractures.