Skeletal System & Bone Tissue Vocabulary

Vocabulary flashcards covering key terms related to skeleton divisions, bone structure, cell types, matrices, and clinical applications.

Axial skeleton

Division of the skeleton consisting of the skull, vertebral column, sternum, and ribs.

Appendicular skeleton

Division of the skeleton composed of upper and lower limbs, plus the pectoral and pelvic girdles, hands, and feet.

Osseous tissue

The supportive connective (bone) tissue forming the bulk of bones; exists as compact or spongy bone.

Compact (cortical) bone

Dense, strong bone tissue that withstands compression, twisting, and shear forces.

Spongy (cancellous/trabecular) bone

Porous bone tissue with trabeculae; supports weight shifts and houses marrow.

Red marrow

Bone marrow type that contains hematopoietic stem cells and produces blood cells.

Yellow marrow

Marrow rich in adipocytes; functions primarily as a fat storage site.

Periosteum

Vascular, innervated dense irregular connective tissue membrane covering bone’s outer surface.

Perforating fibers

Collagen fibers that anchor the periosteum firmly to underlying bone.

Trabeculae

Honey-comb-like bony plates forming the framework of spongy bone.

Endosteum

Thin connective tissue lining internal bone surfaces and covering trabeculae.

Medullary cavity

Central marrow-filled cavity within the diaphysis of long bones.

Diaphysis

The shaft or long axis of a long bone, mainly compact bone surrounding the medullary cavity.

Epiphysis

Proximal or distal rounded end of a long bone containing abundant spongy bone.

Metaphysis

Narrow neck region between diaphysis and epiphysis; major site of bone growth.

Epiphyseal plate (growth plate)

Hyaline cartilage region where lengthwise bone growth occurs during childhood/adolescence.

Epiphyseal line

Remnant of the epiphyseal plate visible in adults after ossification has stopped.

Diploë

Spongy bone layer sandwiched between compact bone layers of flat bones (e.g., skull).

Sinus (cranial)

Air-filled cavity within some irregular skull bones, lined by mucous membrane.

Hematopoietic stem cells

Blood-forming stem cells found mainly in red marrow (and in peripheral or cord blood).

Osteoblast

Bone-building cell that secretes organic and inorganic matrix during ossification.

Osteocyte

Mature osteoblast trapped in a lacuna; maintains bone matrix and senses mechanical stress.

Osteoclast

Large multinucleated cell derived from macrophages that performs bone resorption.

Osteoprogenitor (osteogenic) cell

Mitotically active stem cell that differentiates into osteoblasts during bone formation.

Ossification

Regulated process of bone tissue formation by osteoblasts.

Calcification (pathologic)

Unregulated deposition of calcium salts in body tissues other than bone.

Bone resorption

Breakdown of bone matrix by osteoclasts via acids and metalloproteases.

Wolff’s law

Principle stating that bone remodels and adapts according to the loads placed upon it.

Inorganic matrix

Mineral portion (≈65 %) of bone composed mainly of hydroxyapatite crystals; gives strength.

Organic matrix (osteoid)

Protein-rich portion (≈35 %) of bone containing collagen, proteoglycans, and glycoproteins; provides flexibility.

Hydroxyapatite

Calcium-phosphate mineral (Ca₅(PO₄)₃OH) that hardens bone and resists compression.

Osteon (Haversian system)

Microscopic structural unit of compact bone consisting of concentric lamellae around a central canal.

Concentric lamellae

Thin rings of bone matrix within an osteon arranged around the central canal.

Central (Haversian) canal

Channel at the center of an osteon that houses blood vessels and nerves.

Perforating (Volkmann’s) canals

Transverse canals connecting central canals of adjacent osteons for vascular/nervous supply.

Canaliculi

Tiny canals that link lacunae, allowing osteocyte processes to exchange nutrients and signals.

Interstitial lamellae

Partial lamellar remnants between intact osteons, evidence of bone remodeling.

Bone marrow transplant

Procedure replacing destroyed marrow with healthy stem cells; can be autologous, syngeneic, or allogeneic.

Autologous transplant

Bone marrow or stem cell transplant in which the patient receives their own harvested cells.

Syngeneic transplant

Stem cell transplant using marrow from an identical twin.

Allogeneic transplant

Stem cell transplant using marrow from a genetically matched but non-identical donor.

GM-CSF (granulocyte-macrophage colony-stimulating factor)

Growth factor that stimulates neutrophil production and mobilizes stem cells into the bloodstream.

G-CSF (granulocyte colony-stimulating factor)

Growth factor used clinically to mobilize hematopoietic stem cells and boost neutrophil counts.

Compact vs. spongy bone

Compact bone is dense and forms the outer shell; spongy bone is porous and internal, housing marrow.