Skeletal System: Intro, Microanatomy, and Bone Formation

Vocabulary practice cards covering bone development, bone cell types, microscopic and gross anatomy, cartilage growth, and bone markings across all lecture modules.

Osteogenesis (Ossification)

The process of bone tissue formation that includes initial embryo bone formation starting at 8 weeks, bone growth until early adulthood, and lifelong bone remodeling and repair.

Endochondral Ossification

The bone formation process in which bone forms by replacing pre-existing hyaline cartilage models, forming essentially all bones inferior to the base of the skull except the clavicles.

Intramembranous Ossification

The process of bone formation where bone develops directly from fibrous connective tissue membranes formed by mesenchymal cells, forming the frontal, parietal, occipital, temporal, and clavicle bones.

Primary Ossification Center

The region located in the center of the hyaline cartilage diaphysis where endochondral ossification initiates in month 2 of fetal development.

Periosteal Bud

A structure consisting of blood vessels, nerves, red marrow, osteogenic cells, and osteoclasts that invades calcified cartilage cavities during step 3 of endochondral ossification.

Secondary Ossification Centers

Sites of bone formation that appear in the epiphyses of long bones around the time of birth during endochondral ossification.

Woven Bone

An early, unorganized network of trabeculae formed during intramembranous ossification when osteoid is laid down between embryonic blood vessels.

Diploë

The internal layer of spongy bone situated between two parallel plates of compact bone in short, flat, and irregular bones.

Osteogenic Cells

Mitotically active stem cells located in the periosteum and endosteum that differentiate into osteoblasts or bone-lining cells when stimulated.

Osteoblasts

Actively mitotic bone-forming cells that secrete unmineralized bone matrix called osteoid.

Osteoid

The unmineralized organic bone matrix secreted by osteoblasts, comprising one-third of the organic matrix and made of ground substance and collagen fibers.

Osteocytes

Mature, non-dividing bone cells housed in lacunae that maintain the bone matrix and function as stress or strain sensors.

Bone-Lining Cells

Flat cells located on bone surfaces that assist in matrix maintenance, called periosteal cells on external surfaces and endosteal cells on internal surfaces.

Osteoclasts

Giant, multinucleate cells derived from hematopoietic stem cells that function in bone resorption.

Resorption Bays

Shallow depressions on bone surfaces where active osteoclasts reside during the breakdown of bone matrix.

Osteon (Haversian System)

The structural unit of compact bone, consisting of an elongated weight-bearing cylinder of concentric lamellae running parallel to the long axis of the bone.

Concentric Lamellae

Rings of bone matrix within an osteon containing collagen fibers that run in alternating directions in adjacent rings to resist twisting stress (torsion).

Central Canal (Haversian Canal)

A central channel running through the core of an osteon that contains blood vessels and nerve fibers.

Perforating Canals (Volkmann's Canals)

Canals lined with endosteum lying at right angles to the central canal, connecting blood vessels and nerves of the periosteum, medullary cavity, and central canals.

Lacunae

Small cavities within the bone matrix that contain mature osteocytes.

Canaliculi

Hairlike canals connecting lacunae to each other and to the central canal, allowing cell projections with gap junctions to relay nutrients and wastes between osteocytes.

Interstitial Lamellae

Incomplete lamellae lying between intact osteons that fill gaps or represent remnants of older osteons cut by remodeling.

Circumferential Lamellae

Lamellae that extend around the entire outer and inner circumference of the diaphysis, deep to the periosteum and superficial to the endosteum, to resist twisting.

Trabeculae

Small, needle-like or flat pieces of bone aligned along lines of stress that form the structural framework of spongy bone.

Hydroxyapatites

Inorganic mineral salts (primarily calcium phosphate) that make up $65\%$ of bone mass and provide bone hardness and resistance to compression.

Hematopoiesis

The process of blood cell formation occurring within the red marrow cavities of spongy bone.

Osteocalcin

A hormone secreted by bone cells that helps regulate insulin secretion, glucose levels, and metabolism.

Axial Skeleton

The anatomical division formed along the long axis of the body, comprising the skull, vertebral column, and rib cage.

Appendicular Skeleton

The anatomical division comprising upper and lower limb bones and the pectoral and pelvic girdles that attach limbs to the axial skeleton.

Long Bones

Bones that are longer than they are wide, consisting of a shaft plus two ends.

Short Bones

Cube-shaped bones located in the wrist and ankle.

Sesamoid Bones

A special type of short bone that forms within a tendon, such as the patella.

Flat Bones

Thin, flattened, and usually slightly curved bones, including the sternum, scapulae, ribs, and most skull bones.

Irregular Bones

Bones with complicated shapes that do not fit other categories, such as vertebrae and hip bones.

Perichondrium

A layer of dense irregular connective tissue surrounding cartilage that acts like a girdle to resist outward expansion and contains blood vessels.

Hyaline Cartilage

The most abundant skeletal cartilage type, containing collagen fibers only, providing support, flexibility, and resilience in articular, costal, respiratory, and nasal areas.

Elastic Cartilage

Skeletal cartilage similar to hyaline cartilage but rich in elastic fibers, located in the external ear and epiglottis.

Fibrocartilage

Cartilage with thick collagen fibers possessing great tensile strength, found in the knee menisci and intervertebral discs.

Appositional Growth

Cartilage growth in which cartilage-forming cells in the perichondrium secrete new matrix against the external face of existing cartilage.

Interstitial Growth

Cartilage growth in which chondrocytes within lacunae divide and secrete new matrix, expanding cartilage from within.

Diaphysis

The tubular shaft forming the long axis of a long bone, constructed of compact bone surrounding a central medullary cavity.

Epiphyses

The expanded proximal and distal ends of a long bone, consisting of an outer compact bone shell surrounding spongy bone internally.

Epiphyseal Line

A line of dense bone between the diaphysis and epiphysis of adult long bones, representing the remnant of the childhood epiphyseal plate.

Periosteum

A white, double-layered connective tissue membrane covering external bone surfaces, containing an outer fibrous layer and an inner osteogenic layer.

Perforating (Sharpey's) Fibers

Tufts of collagen fibers that extend from the fibrous layer of the periosteum into the bone matrix, anchoring the periosteum to bone.

Endosteum

A delicate connective tissue membrane covering internal bone surfaces, lining canals of compact bone and covering trabeculae of spongy bone.

Tuberosity

A large, rounded, often roughened bone projection that serves as a site for muscle and ligament attachment.

Foramen

A round or oval opening through a bone that serves as a passageway for blood vessels and nerves.

Fossa

A shallow, basinlike depression in a bone, often serving as an articular surface.

Trochanter

A very large, blunt, irregularly shaped process serving as a site for muscle attachment, found exclusively on the femur.