Unit 2 Study Guide: Skeletal System Vocabulary

Flashcard deck containing key vocabulary terms, structures, physiological processes, and joint classifications listed in Unit 2 Skeletal System study guide.

Bone

An organ composed of osseous tissue, cartilage, dense connective tissue, epithelium, adipose tissue, and nervous tissue, serving as part of the structural framework of the body.

Osseous tissue

A specialized connective tissue with a hardened matrix containing calcium phosphate and other minerals, forming the primary structural component of bones.

Calcification

The physiological process in which organic bone matrix becomes hardened by the deposition of calcium salts and mineral crystals.

Flat bone

A type of bone characterized by thin, flattened, and often curved surfaces (e.g., cranial bones, sternum, ribs) that protect internal organs and offer broad areas for muscle attachment.

Long bone

A type of bone that is distinctly longer than it is wide, consisting of a central shaft (diaphysis) and two expanded ends (epiphyses), such as the femur or humerus.

Short bone

A type of bone that is roughly cube-shaped or equal in length and width, such as the carpal and tarsal bones.

Irregular bone

A bone with a complex or elaborate shape that does not fit into flat, long, or short categories, such as vertebrae and facial bones.

Compact (dense) bone

Dense, rigid osseous tissue organized into osteons that forms the hard outer shell of bones and resists mechanical stress.

Spongy (cancellous) bone

Latticework bone tissue composed of trabeculae and spicules, containing spaces filled with bone marrow.

Marrow cavity

The hollow internal space within the diaphysis of a long bone containing bone marrow.

Diaphysis

The elongated, cylindrical shaft of a long bone that encloses the marrow cavity.

Metaphysis

The growth zone of a long bone located between the diaphysis and epiphysis, housing the epiphyseal plate or line.

Epiphysis

The expanded terminal portion of a long bone that articulates with an adjacent bone.

Epiphyseal line

The dense bony line remaining in adult bones marking the site where the epiphyseal plate fused after longitudinal growth completed.

Epiphyseal plate

A layer of hyaline cartilage in the metaphysis of growing long bones that permits elongation through interstitial growth.

Articular cartilage

A smooth layer of hyaline cartilage covering joint surfaces of epiphyses to reduce friction and absorb impact at synovial joints.

Periosteum

A double-layered fibrous membrane covering the external surface of bones, serving as an attachment site for tendons and housing bone-forming cells.

Endosteum

A thin layer of connective tissue lining internal bone cavities, central canals, and trabeculae.

Osteogenic cells

Stem cells derived from mesenchyme located in the endosteum and periosteum that divide to produce osteoblasts.

Osteoblasts

Bone-forming cells that synthesize and secrete organic matrix components and initiate calcification.

Osteocytes

Mature, non-dividing bone cells trapped within lacunae that maintain bone matrix and monitor physical strain.

Lacunae

Small cavities or spaces within calcified bone matrix containing osteocytes.

Osteoclasts

Large multinucleated cells responsible for bone resorption and mineral dissolution during bone remodeling.

Osteogenesis

The process of bone tissue formation, also referred to as ossification.

Hydroxyapatite

The primary inorganic mineral component of bone matrix, composed of crystallized calcium phosphate $Ca_{10}(PO_4)_6(OH)_2$.

Osteon

The basic microscopic structural unit of compact bone consisting of concentric lamellae surrounding a central canal.

Lamellae

Concentric or parallel rings of calcified matrix within osteons and bone tissue.

Central canal

A longitudinal channel passing through the middle of an osteon that contains blood vessels and nerves.

Trabeculae

Thin plates or struts of bone tissue forming the supportive lattice of spongy bone.

Spicules

Small needle-like spikes of bone matrix formed during early stages of bone development.

Red bone marrow

Hemopoietic tissue located within spongy bone spaces that produces blood cells.

Yellow bone marrow

Adipose-rich tissue occupying the medullary cavities of adult long bones, serving as energy storage.

Ossification

The conversion of embryonic mesenchymal or cartilaginous tissue into bone.

Intramembranous ossification

A process of bone formation in which bone develops directly from fibrous connective tissue sheets, creating flat bones of the skull and clavicles.

Endochondral ossification

A process of bone formation where a hyaline cartilage model is replaced by bone tissue.

Ossification center

The initial cluster of mesenchymal cells that differentiate into osteoblasts and begin depositing bone matrix during development.

Mesenchymal cell

An embryonic connective tissue stem cell that gives rise to osteogenic cells and other skeletal tissue cell types.

Interstitial growth

Growth in length occurring within cartilage at the epiphyseal plate.

Appositional growth

Growth in diameter or thickness resulting from the deposition of new matrix at the bone surface by periosteal osteoblasts.

Hypocalcemia

A homeostatic imbalance characterized by abnormally low blood calcium concentrations.

Hypercalcemia

A homeostatic imbalance characterized by abnormally high blood calcium concentrations.

Calcitriol

The active form of Vitamin D that raises blood calcium concentration by increasing intestinal absorption.

Calcitonin

A hormone produced by the thyroid gland that lowers blood calcium levels by inhibiting osteoclasts and promoting osteoblast activity.

Parathyroid hormone

A hormone secreted by parathyroid glands that elevates blood calcium levels by stimulating osteoclast activity and renal calcium reabsorption.

Fracture

A physical crack or break in the continuity of a bone.

Osteoporosis

A disorder characterized by reduced bone mass and structural deterioration, making bones brittle and prone to fracture.

Axial skeleton

The central structural axis of the skeleton comprising the skull, auditory ossicles, hyoid bone, vertebral column, and thoracic cage.

Appendicular skeleton

The section of the skeletal system comprising the bones of the limbs and pectoral and pelvic girdles.

Foramen

A hole or passageway through bone that allows passage for nerves and blood vessels.

Process

Any prominent projection or outgrowth extending from a bone.

Suture

An immovable fibrous joint binding together bones of the skull.

Joint/articulation

Any site where two or more bones meet.

Bony joint

An immovable joint formed when the space between two bones fuses into a single continuous bone.

Synostosis

The fusion of two bones to form a single immovable bony joint.

Fibrous joint

A joint held together by collagen fibers with little to no movement.

Synarthrosis

A functional class of joints that allows no movement.

Gomphosis

A fibrous joint anchoring a tooth into its bony socket via periodontal ligaments.

Syndesmosis

A fibrous joint bound by longer collagenous ligaments or membranes that allow limited movement.

Cartilaginous joint

A joint in which bones are held together by hyaline cartilage or fibrocartilage.

Amphiarthrosis

A functional class of joints allowing slight movement.

Synchondrosis

A cartilaginous joint joined by hyaline cartilage.

Symphysis

A cartilaginous joint joined by a pad or plate of fibrocartilage.

Synovial joint

A freely movable joint enclosed by a fluid-filled cavity and joint capsule.

Diarthrosis

A functional class of joints that allows free movement.

Synovial fluid

A viscous fluid contained within synovial joints that lubricates joint surfaces and nourishes cartilage.

Joint capsule

A double-layered structure enclosing a synovial joint cavity, consisting of an outer fibrous capsule and inner synovial membrane.

Meniscus

A crescent-shaped pad of fibrocartilage within a synovial cavity that absorbs shock and improves joint articulation.

Tendon

A cord-like band of dense collagenous tissue attaching a muscle to a bone.

Ligament

A band of dense fibrous tissue connecting bone to bone across a joint.

Bursa

A fluid-filled fibrous sac lined with synovial membrane that cushions and reduces friction between moving structures.

Ball-and-socket joint

A multiaxial synovial joint where a spherical head fits into a rounded socket, permitting wide range of motion.

Condylar joint

A biaxial synovial joint where an oval convex surface fits into an elliptical depression.

Saddle joint

A biaxial joint with saddle-shaped concave and convex surfaces on both articulating bones.

Plane joint

A nonaxial or biaxial synovial joint with flat articulating surfaces that slide across one another.

Hinge joint

A monoaxial synovial joint permitting motion restricted to a single plane.

Pivot joint

A monoaxial synovial joint in which a bone rotates around its own longitudinal axis.

Flexion

A movement that decreases the angle between articulating bones.

Extension

A movement that increases the angle between articulating bones, straightening them toward anatomical position.

Abduction

Movement of a body part away from the midline in the frontal plane.

Adduction

Movement of a body part toward the midline in the frontal plane.

Elevation

Superior movement of a body part in the frontal plane.

Depression

Inferior movement of a body part in the frontal plane.

Protraction

Anterior movement of a body part in the transverse plane.

Retraction

Posterior movement of a body part in the transverse plane.

Rotation

Movement of a bone turning around its central longitudinal axis.

Pronation

Medial rotation of the forearm positioning the palm posteriorly or downward.

Supination

Lateral rotation of the forearm returning the palm to anatomical position (facing anteriorly).

Excursion

Side-to-side movement of the mandible away from the midline.

Opposition

Movement of the thumb across the palm to touch the tip of another finger.

Dorsiflexion

Ankle movement bringing the toes and foot superiorly toward the shin.

Plantarflexion

Ankle movement pressing the foot downward and pointing the toes.

Inversion

Foot movement turning the sole medially.

Eversion

Foot movement turning the sole laterally.