Skeletal System Bio 211

Skeletal System Components?

Bones, ligaments, and cartilage.

Tissue type of bone?

Connective tissue (specifically osseous connective tissue).

Organic portion of bone ECM?

Osteoid, which consists of collagen and proteoglycans secreted by osteoblasts.

Inorganic portion of bone ECM?

Salt crystals, mostly calcium phosphate, which deposit on collagen fibers and result in mineralization.

Bone rebar analogy?

Collagen fibers provide flexibility and tensile strength; without them, bones shatter.

Bone concrete analogy?

Hydroxyapatite crystals provide hardness and compression resistance; without them, bones bend.

Osteoprogenitor cells?

Stem cells located in the periosteum and endosteum that divide to produce committed cells that become osteoblasts.

Osteoblasts?

Highly active bone cells that form and secrete the osteoid matrix to promote bone growth and healing.

Osteocytes?

Mature bone cells trapped in the matrix that reside in lacunae, detect injury, and signal osteoblasts to direct repair.

Osteoclasts?

Large phagocytic cells that break down bone tissue during bone resorption.

Compact Bone Microstructure?

Composed of structural units called osteons (Haversian systems) with concentric rings.

Spongy Bone Microstructure?

Composed of a lattice-like meshwork called trabeculae, designed to withstand multidirectional stress.

Central canal (Haversian canal)?

The central opening of an osteon containing blood vessels and nerves.

Concentric lamellae?

Rings of bone matrix surrounding the central canal, with fibers oriented at 90 degrees in adjacent rings for strength.

Lacunae?

Small spaces between concentric lamellae that house osteocytes.

Canaliculi?

Tiny channels connecting lacunae that provide paths for communication and nutrient supply from the blood source.

Perforating canals?

Channels running perpendicular to osteons that connect central canals to the outermost periosteum.

Hyaline cartilage function?

Provides smooth surfaces, flexibility, and support; serves as the precursor model for bone formation and growth.

Hyaline cartilage locations?

Costal cartilage (ribs), articular cartilage (joints), and epiphyseal plates (growth plates).

Fibrocartilage function?

Withstands compression, is very strong, acts as a precursor to new bone at injury sites (soft callus), and connects skeletal structures.

Fibrocartilage locations?

Intervertebral discs, pubic symphysis, and the lateral/medial menisci of the knee.

Cartilage regeneration capability?

Poorly regenerative due to being poorly vascularized.

Interstitial growth?

Cartilage growth from within where chondrocytes undergo mitosis, become chondroblasts, secrete matrix, separate into independent lacunae, and increase cartilage length.

Appositional growth?

Cartilage growth along the periphery where stem cells in the perichondrium divide into chondroblasts, secrete matrix at the edge, and increase cartilage width.

Interstitial vs Appositional timeline?

Interstitial growth stops after birth; appositional growth stops when overall body growth is complete.

Diaphysis?

The elongated shaft of a long bone consisting of a compact bone cylinder that provides leverage for movement.

Epiphysis?

The proximal and distal ends of a long bone composed of a thin compact outer layer filled with spongy bone to resist stress.

Metaphysis?

The region between the epiphysis and diaphysis containing the epiphyseal plate in growing bone.

Epiphyseal plate?

A layer of hyaline cartilage in the metaphysis where lengthwise bone growth occurs; turns into an epiphyseal line once growth ends.

Medullary canal (marrow cavity)?

The open central space within the diaphysis containing red marrow in children and yellow marrow in adults.

Red bone marrow function?

The site of hematopoiesis (blood cell genesis) located in the spongy bone and child medullary cavities.

Yellow bone marrow function?

Adipose tissue serving as energy storage located in the medullary cavity of adult long bones.

Periosteum?

Outer dense irregular connective tissue layer covering bone that contains osteoprogenitor cells and osteoblasts; anchors tendons and ligaments.

Endosteum?

Delicate reticular connective tissue lining internal bone surfaces (like the medullary cavity) containing osteoprogenitor cells, osteoblasts, and osteoclasts.

Long bones?

Bones whose length is greater than their width (e.g., femur).

Short bones?

Bones whose length is roughly equal to their width (e.g., tarsal bone).

Flat bones?

Bones featuring flat, thin surfaces (e.g., frontal bone of skull).

Irregular bones?

Bones displaying complex, elaborate shapes (e.g., vertebra).

Sesamoid bones?

Bones that are uniquely encased entirely within a tendon.

General structure of non-long bones?

Outside is made of compact bone, and the inside is made of spongy bone (diploë in flat skull bones).

Intramembranous ossification?

Bone formation during embryonic/fetal development where mesenchyme (embryonic connective tissue) directly ossifies into bone.

Intramembranous bone examples?

Bones of the skull, face, and the clavicle.

Endochondral ossification?

Bone formation that begins with a hyaline cartilage model which calcifies from the center outward; forms long bones.

Zone 1 (Zone of resting cartilage)?

Layer of hyaline cartilage securing the epiphyseal plate to the epiphysis; houses resting stem cells.

Zone 2 (Zone of proliferating cartilage)?

Area of rapid mitosis where dividing chondrocytes align into distinct vertical columns.

Zone 3 (Zone of hypertrophic cartilage)?

Region where chondrocytes stop dividing and significantly enlarge in size.

Zone 4 (Zone of calcified cartilage)?

Area where minerals deposit into the matrix, restricting nutrient delivery and killing off the chondrocytes.

Zone 5 (Zone of ossification)?

Region where lacunae walls break down, and invading blood vessels/osteoblasts lay down matrix to form new bone.

Appositional bone growth?

Width growth at the periosteum where osteoblasts lay down concentric lamellae externally while internal osteoclasts resorb bone to enlarge the medullary cavity.

Bone remodeling?

A lifelong process replacing roughly 20% of the skeleton yearly through coordinated old bone removal and new bone deposition.

Mechanical stress role?

Weight-bearing exercise causes mechanical stress necessary to stimulate bone remodeling and maintain bone health with age.

Growth Hormone (Somatotropin)?

Stimulates the liver to produce insulin-like growth factor, causing cartilage growth at the epiphyseal plate for bone elongation.

Acromegaly?

Clinical condition resulting from too much growth hormone activity.

Thyroid Hormone?

Stimulates osteoblast activity to promote healthy bone growth.

Calcitonin?

Hormone released to promote calcium deposition into bone matrix by turning off osteoclast activity.

Parathyroid Hormone (PTH)?

Hormone that increases blood calcium levels by turning on osteoclasts to resorb bone and signaling kidneys to retain calcium.

Sex Hormones (Estrogen & Testosterone)?

Early rising levels stimulate osteoblasts; higher adult levels during puberty encourage epiphyseal plate closure.

Glucocorticoids (Cortisone)?

Hormones that increase osteoclast activity and decrease osteoblast activity; impairs child bone growth.

Calcitriol (Vitamin D)?

Hormone synthesized via UV sunlight skin conversion required for absorbing dietary calcium from the small intestine.

Essential uses of blood calcium?

Required for vital physiological processes like muscle contraction and generating nerve impulses.

Osteopenia?

A clinical state demonstrating lower than normal bone mineral density.

Osteoporosis?

A severe skeletal disease defined by a 2.5 standard deviation decrease in normal bone density.

Fracture?

Any distinct break in the structural integrity of a bone.

Stress fracture?

A thin break in bone integrity caused by repeated pressure or impact.

Pathological fracture?

A fracture occurring because an underlying disease process (like cancer) has weakened the bone.

Simple fracture?

A closed bone break where the bone does not pierce through the surface of the skin.

Compound fracture?

An open bone break where the broken ends of the bone protrude out through the skin.

Colles fracture?

Fracture of the distal end of the lateral forearm bone (radius) that produces a "dinner fork" deformity.

Comminuted fracture?

A fracture type where the bone is splintered or crushed into several small pieces.

Greenstick fracture?

A partial fracture where one side of the bone breaks and the other side bends; more commonly seen in children.

Spiral fracture?

A fracture that spirals around the axis of a long bone resulting from intense twisting stress.

Step 1 of Fracture Healing?

A fracture hematoma (blood clot) forms from ruptured blood vessels within the bone and periosteum.

Step 2 of Fracture Healing?

A fibrocartilaginous (soft) callus forms as regenerating blood vessels invade and fibrocartilage bridges the gap.

Step 3 of Fracture Healing?

A bony (hard) callus forms as osteoblasts replace the soft fibrocartilage callus with primary bone.

Step 4 of Fracture Healing?

The bone is remodeled over time as osteoclasts remove excess material and compact bone replaces primary bone.