Skip to main content
Back

Bone Physiology and the Skeletal System: Study Guide

NotesPracticeVideo lessons

Study Guide - Smart Notes

Tailored notes based on your materials, expanded with key definitions, examples, and context.

Bone Physiology

Overview of Bone as Living Tissue

Bone is a dynamic, living tissue that undergoes continuous remodeling and repair. It contains living cells that maintain the mineralized matrix and can repair itself after injury.

  • Remodeling: Ongoing process in adults, replacing about 10% of bone mass per year.

  • Calcium Homeostasis: Calcium salts are deposited in bone when blood calcium is high and removed when low.

  • Effect of Stress: Physical stress stimulates bone remodeling and strengthening.

  • Key Minerals: Primary: calcium, phosphate; Secondary: calcium carbonate, magnesium.

Bone Structure and Components

  • Medullary Cavity: Central hollow region in long bones containing bone marrow.

  • Periosteum: Outer membrane with two layers:

    • Osteogenic Layer: Contains stem cells for bone growth and repair.

    • Fibrous Layer: Contains blood vessels and nerves; provides protection.

  • Endosteum: Inner membrane lining the medullary cavity.

  • Epiphysis: Ends of long bones, containing spongy bone and red marrow.

  • Epiphyseal Cartilage (Growth Plate): Zone of cartilage at bone ends allowing lengthwise growth; replaced by bone at adult height.

  • Red Bone Marrow: Site of hematopoiesis (production of erythrocytes, leukocytes, and thrombocytes).

Bone Matrix

  • Inorganic Component: Calcium salts (hydroxyapatite) provide strength.

  • Organic Component: Collagen fibers provide flexibility.

Bone Cells

  • Osteoprogenitor Cells: Stem cells that differentiate into osteoblasts.

  • Osteoblasts: Bone-forming cells; secrete bone matrix.

  • Osteocytes: Mature bone cells; maintain bone tissue.

  • Osteoclasts: Bone-resorbing cells derived from hemopoietic lineage; break down bone to release calcium.

Note: Osteoclasts are unique as they originate from blood cell precursors, not the osteoprogenitor pathway.

Comparison of Compact and Spongy Bone

Feature

Compact Bone

Spongy Bone

Lamellae

Yes

No

Lacunae

Yes

Yes

Canaliculi

Yes

Yes, but small

Haversian (Central) Canal

Yes

No

Trabeculae

No

Yes

Osteocytes

Yes

Yes

Location/Nature

80%, Dense, shaft region

20%, Light, ends of long bones, skull

Blood Supply in Bone

  • Haversian (Central) Canal: Supplies blood to each osteon in compact bone.

  • Volkmann's Canal: Runs perpendicular to Haversian canals, connecting blood vessels across the bone shaft.

Bone Growth

  • Appositional Growth: Increases bone diameter by adding new bone under the periosteum.

  • Interstitial Growth: Increases bone length at the epiphyseal (growth) plates.

Bone Formation (Ossification)

  • Osteogenesis/Ossification: Process of bone formation from mesenchymal tissue.

  • Types of Bone Tissue: Compact (dense outer layer) and spongy (cancellous, inner layer).

Endochondral Ossification

  • Forms most bones, especially long bones.

  • Process:

    1. Mesenchymal cells form a cartilage model.

    2. Chondrocytes in the center hypertrophy and mineralize.

    3. Chondrocytes die; blood vessels invade, bringing osteogenic cells.

    4. Primary ossification center forms in diaphysis (shaft).

    5. Secondary ossification centers form in epiphyses (ends).

Intramembranous Ossification

  • Forms flat bones (e.g., skull, clavicle).

  • Process:

    1. Mesenchymal cells differentiate into osteoblasts, forming ossification centers.

    2. Osteoblasts secrete osteoid, become osteocytes.

    3. Trabecular bone and periosteum form.

    4. Superficial plates of bone develop.

    5. Blood vessels form red marrow.

    6. Red and white blood cell production continues throughout life.

Cartilage in Adult Bones

  • Articular cartilage remains at joint surfaces.

  • Intercostal cartilage persists in the rib cage.

Growth Plate (Epiphyseal Plate)

  • Site of interstitial growth in length.

  • Calcifies and closes at adulthood (females ~18, males ~25).

  • Growth in width (appositional) continues with mechanical stress and adequate nutrition.

Hormonal Regulation of Bone

  • Parathyroid Hormone (PTH): Released when blood calcium is low; stimulates osteoclasts to release calcium from bone.

  • Calcitonin: Released after meals; stimulates osteocytes to uptake calcium, lowering blood calcium levels.

Bone Repair

  1. Hematoma formation (blood clot at fracture site).

  2. Fibrocartilaginous callus formation.

  3. Spongy bone replaces fibrocartilage (ossification).

  4. Remodeling into compact bone.

Types of Bone Fractures

  • Colles’s Fracture: Distal radius fracture near the wrist, common from falls.

  • Clavicle Fracture: Often from falls on the shoulder.

  • Potts Fracture: Fracture of tibia and/or fibula near the ankle, often with dislocation.

  • Greenstick Fracture: Incomplete fracture in children; bone bends and cracks on one side.

  • Compound (Open) Fracture: Bone breaks through the skin, increasing infection risk.

Skeletal System

Key Structures and Articulations

  • Meniscus: Fibrocartilage pads in the knee for shock absorption (medial and lateral).

  • Occipital Bone: Articulates with the atlas (C1 vertebra); allows for head flexion/extension.

  • Scapula: Connected to axial skeleton via ligaments at the sternoclavicular joint and muscles to the thoracic region.

Major Joints and Bones Involved

Joint

Bones Involved

Elbow

Humerus, radius, ulna

Wrist

Carpals (scaphoid, lunate, triquetrum, pisiform, trapezium, trapezoid, capitate, hamate), radius, ulna

Knee

Patella, tibia, femur

Hip

Ilium, ischium, pubis, femur

Shoulder

Clavicle, scapula, humerus

Ankle

Talus, fibula, tibia

Other Skeletal Features

  • Sacrum: Joins the os coxa (hip bone) as part of the axial skeleton.

  • Proximal Tibia: Articulates with fibula and femur.

  • Coccyx: Attaches to sacrum.

  • Hyoid Bone: Does not form a joint with other bones.

  • TMJ (Temporomandibular Joint): Only moveable skull joint (mandible to temporal bone).

  • Fibula: Articulates with talus and tibia.

  • Metacarpal I: Proximal end articulates with the trapezium (carpal bone).

  • Phalanges: Distal end of proximal phalanx II forms a joint with proximal end of medial phalanx II.

  • Intervertebral Disc: Composed of annulus fibrosus (outer ring) and nucleus pulposus (inner gel).

  • Clavicle: Forms joints with sternum and scapula.

  • Os Coxa: Composed of ilium, ischium, and pubis.

  • Pelvis: Includes os coxa, sacrum, and coccyx.

  • Conchae: Curved bones in the nasal cavity, increase surface area to warm and moisten air.

  • Sinus-Containing Bones: Ethmoid, sphenoid, maxilla, frontal.

Spinal Curvatures and Conditions

  • Kyphosis: Exaggerated thoracic curvature (hunchback).

  • Scoliosis: Lateral curvature of the spine.

  • Lordosis: Exaggerated lumbar curvature (swayback).

  • Normal Adult Spine: Four curves:

    • Thoracic and sacral (present at birth, C-shaped in infants).

    • Cervical and lumbar (develop with sitting, standing, walking).

Additional info:

  • Growth plates (epiphyseal plates) are visible on X-rays in children due to lower mineral content.

  • Mechanical stress and physical activity are essential for maintaining bone mass throughout life.

Pearson Logo

Study Prep