Bone Tissue and the Skeletal System: every key term you need (+ practice quiz)
25 flashcard terms for Anatomy & Physiology I Topic 5, written to match the course framework. Study them here, then drill them as interactive flashcards, or test yourself with the 15-question quiz — free, no account needed.
Support of soft tissue, protection of organs, leverage for muscular movement, mineral and growth factor storage, blood cell formation in red marrow, and triglyceride storage in yellow marrow.
Compact bone
The dense outer bone layer that appears solid to the unaided eye. It is organized into cylindrical osteons aligned with lines of stress and resists bending and torsion applied along the shaft.
Spongy bone
Internal bone composed of an open lattice of trabeculae oriented along stress lines. It reduces skeletal weight, houses marrow, and redistributes force at the ends of long bones.
Osteon
The structural unit of compact bone, a set of concentric lamellae surrounding a central canal that carries vessels and nerves. Collagen fiber direction alternates between lamellae to resist twisting.
Lacuna and canaliculus
The small cavity housing a bone cell and the hair-thin channel connecting neighboring cavities. Cell processes within canaliculi allow nutrients and signals to reach cells trapped in mineralized matrix.
Osteoblast
The bone-forming cell that secretes the collagen-rich organic matrix and initiates its mineralization. When surrounded by the matrix it has produced, it matures into a resident osteocyte.
Osteocyte
A mature bone cell occupying a lacuna and communicating through canaliculi. It monitors mechanical strain and matrix condition and signals for remodeling when loading patterns change.
Osteoclast
A large multinucleate cell derived from a monocyte lineage that dissolves bone by secreting acid and lysosomal enzymes onto the matrix from its ruffled border, releasing calcium into the blood.
Osteogenic cell
The mitotic stem cell of bone tissue, found in the inner periosteum and the endosteum. It divides to supply new bone-forming cells during growth, remodeling and fracture repair.
Bone matrix composition
About one third organic material, mainly collagen giving flexibility and tensile strength, and two thirds inorganic hydroxyapatite crystals of calcium phosphate giving hardness and compressive strength.
Periosteum
The double-layered membrane covering the outer bone surface except at joint cartilage. Its fibrous outer layer anchors tendons and ligaments, and its cellular inner layer supplies cells for appositional growth.
Endosteum
The thin cellular membrane lining internal bone surfaces, including the marrow cavity and the canals of compact bone. It contains bone-forming and bone-resorbing cells active in remodeling.
Diaphysis and epiphysis
The tubular shaft of a long bone and its expanded ends. The shaft is a compact bone cylinder around a marrow cavity; the ends are spongy bone shells capped by articular cartilage.
Epiphyseal plate
The disc of hyaline cartilage between shaft and end in a growing bone. Ordered cartilage proliferation on one face and replacement by bone on the other lengthens the bone until the plate closes.
Intramembranous ossification
Bone formation directly within a fibrous connective tissue membrane, with no cartilage model. It produces the flat bones of the cranial vault, most facial bones and the clavicles.
Endochondral ossification
Bone formation in which a hyaline cartilage model is gradually replaced. A bone collar forms, the cartilage calcifies and deteriorates, vessels invade, and ossification spreads from primary and secondary centers.
Appositional growth
Increase in bone width produced when cells of the inner periosteum add matrix to the outer surface while cells of the endosteum resorb from within, thickening the wall without excessive mass.
Bone remodeling
The lifelong coupled process of resorption and deposition that renews about a tenth of the skeleton each year, repairing microdamage, adapting shape to mechanical demand and adjusting blood calcium.
Wolff law
The observation that a bone remodels in response to the forces placed on it, so trabeculae align with stress lines and heavily loaded regions thicken while unloaded regions lose mass.
Parathyroid hormone in bone
The hormone released when blood calcium falls. It indirectly stimulates bone resorption, raising blood calcium; this regulatory demand takes priority over skeletal strength during sustained hypocalcemia.
Calcitonin
A thyroid hormone released when blood calcium is high that, at pharmacological doses, inhibits bone-dissolving cells. Its physiological role in adults is modest compared with parathyroid hormone.
Axial skeleton
The central bony core formed by the skull, vertebral column, ribs and sternum. It supports the head and trunk, protects the brain, spinal cord and thoracic organs, and anchors respiratory muscles.
Appendicular skeleton
The bones of the upper and lower limbs together with the pectoral and pelvic girdles that attach them to the axial skeleton. Its design favors mobility above and weight bearing below.
Fracture repair
Healing that proceeds through hematoma formation, a soft fibrocartilaginous callus bridging the break, replacement by a bony callus of spongy bone, and finally remodeling into compact bone along stress lines.
Osteoporosis
A condition in which resorption outpaces deposition, thinning trabeculae and enlarging marrow spaces until bones fracture under ordinary loads. Risk rises with age, low estrogen, inactivity and poor calcium intake.