|  | Conditions & Treatments | Broken Bones

Understanding Bone Structure, Function, Growth, and Strategies for Lifelong Bone Health

Bone: Living, Dynamic Tissue

Bone is a specialized connective tissue forming the vertebrate skeleton. It is highly vascularized, innervated, and constantly remodeled—far from inert scaffolding.

Composition

  • Mineral phase (65%): Hydroxyapatite [Ca₁₀(PO₄)₆(OH)₂] — provides hardness, compressive strength.
  • Organic matrix (35%): Type I collagen (90%) + non-collagenous proteins (osteocalcin, osteonectin, bone sialoprotein) — provides tensile strength, flexibility.
  • Water (~10%): Within mineral and matrix.
  • Cells: Osteoblasts (formation), osteoclasts (resorption), osteocytes (mechanosensing, signaling), lining cells.

Structural Types

  • Cortical (compact) bone: Dense outer shell (80% of skeletal mass); high strength, slow turnover.
  • Trabecular (cancellous/spongy) bone: Honeycomb network at epiphyses, vertebral bodies; high surface area, rapid turnover, metabolic reservoir.

Bone Anatomy (Long Bone Example)

  1. Periosteum: Fibrous outer membrane; attachment for tendons/ligaments; contains osteoprogenitor cells, vessels, nerves.
  2. Cortical bone: Dense diaphysis (shaft).
  3. Trabecular bone: Metaphyses/epiphyses; houses bone marrow.
  4. Endosteum: Lines inner cavities; osteogenic.
  5. Bone marrow: Red (hematopoiesis) in axial skeleton; yellow (adipose) in long bone diaphyses.
  6. Articular cartilage: Hyaline cartilage covering joint surfaces.

Key Functions

  • Mechanical: Support, leverage for movement, protection of viscera.
  • Mineral homeostasis: Calcium/phosphate reservoir (99% body Ca, 85% P).
  • Hematopoiesis: Red marrow produces RBCs, WBCs, platelets.
  • Endocrine: Osteocalcin (insulin sensitivity), FGF23 (phosphate), sclerostin (Wnt inhibition).
  • Acid-base buffering: Carbonate release from mineral.

Growth & Remodeling

  • Modeling (growth): Independent formation/resorption at different surfaces → shape/size change. Peaks at puberty; completes ~age 25 (peak bone mass).
  • Remodeling (adult): Coupled resorption-formation in BMUs (basic multicellular units). ~10% of skeleton renewed annually. Repairs microdamage, adapts to load, maintains mineral homeostasis.
  • Regulation: Mechanical loading (Wnt/β-catenin), hormones (PTH, calcitonin, vitamin D, estrogen, testosterone, GH/IGF-1), cytokines (RANKL/OPG).

Common Disorders

  • Osteoporosis: Low bone mass + microarchitectural deterioration → fragility fractures. T-score ≤ -2.5.
  • Osteopenia: T-score -1 to -2.5; precursor.
  • Osteomalacia/rickets: Defective mineralization (vitamin D/phosphate deficiency).
  • Paget's disease: Disordered, excessive remodeling → enlarged, fragile bones.
  • Osteogenesis imperfecta: Genetic collagen defect → brittle bones.

Bone Health Prescription

  • Nutrition: Calcium 1000–1200 mg/day (food first), Vitamin D 800–2000 IU/day (target 25-OH-D >30 ng/mL), protein 1.0–1.2 g/kg, potassium/magnesium (fruits/veg).
  • Exercise: Weight-bearing impact (walking, jumping) + progressive resistance training 2–3×/week.
  • Lifestyle: No smoking, limit alcohol (≤1 drink/day women, ≤2 men), fall prevention.
  • Screening: DEXA at 65 women / 70 men (earlier with risk factors). FRAX for 10-year fracture risk.
  • Pharmacotherapy (if high risk): Bisphosphonates, denosumab, anabolics (teriparatide, romosozumab).

Bone health is built early and maintained lifelong. Invest in your skeleton—it supports everything you do.

Broken Bones - Related Articles