Bone Composition and Structure Quiz

Bone Composition and Structure

• Bone tissue is a specialized connective tissue
• Its properties include hardness, high tensile and compressive resistance
• Main functions are body support, organ protection, calcium deposit and blood cell formation
• Bone structure comes in two forms
  • Compact bone: dense and solid, without cavities
  • Cancellous bone: fine, network-like trabeculae
• Long bones have:
  • Epiphysis: cancellous bone with a thin compact bone layer
  • Metaphysis: hyaline cartilage in children and epiphyseal line in adults
  • Diaphysis: compact bone cylinder with an internal cavity
• Short bones are primarily cancellous bone with a thin compact bone layer
• Periosteum: covers external bone surfaces
  • Dense connective tissue
  • Contains osteoprogenitor cells, osteoblasts, and bone lining cells
• Endosteum: covers internal bone surfaces
  • Includes osteoprogenitor cells

Bone Tissue Components

• Cells:
  • Osteoprogenitor cells
  • Osteoblasts
  • Bone lining cells
  • Osteocytes
  • Osteoclasts
• Extracellular matrix:
  • Mineralized bone matrix
  • Contains hydroxyapatite crystals
  • Fibers and ground substance

Biomechanical Properties of Bone

• Entire Structure:
  • Greater resistance to compression than traction
  • Weak against shear forces
  • Flexural resistance depends on stiffness and fracture load
• Tissue Components:
  • Compact bone: greater resistance to compression than traction; weak against torsion
  • Cancellous bone: greater resistance to compression than traction; trabeculae are reoriented depending on load
• Molecular components:
  • Collagen fibers show initial linear strain under tensile stress, then heterogeneous strain. Changes in mineral composition affect the strain pattern.
  • Hydroxyapatite crystals have greater hardness/elasticity on basal surfaces, but greater resistance on laterals; greater tolerance to microfractures

Biomechanics of Osteons and Individual Trabeculae

• Longitudinal lamellae: resistant to traction and torsion
• Transverse lamellae: resistant to compression, shear, and flexion
• Individual trabeculae: lower longitudinal modulus of elasticity compared to cortical bone osteons

Biomechanics of Molecular Components

• Collagen fibers display initial linear then heterogeneous strain under tensile stress; mineral changes affect the strain pattern.
• Hydroxyapatite crystals show greater hardness/elasticity on basal faces, and higher resistance on laterals, and greater tolerance to microfractures.

Joint Classification

• Structure:
  • Synarthrodial: immovable (sutures)
  • Amphiarthrodial: slightly movable (pubic symphysis)
  • Diarthrodial: freely movable (synovial joints)
• Types of diarthrodial joints (synovial):
  • Ball and socket
  • Hinge
  • Pivot
  • Condylar
  • Saddle
  • Plane

Surgical Effects

• Fractures: Total or partial breakage of bone; open fractures expose the bone, and closed fractures do not.
  • Common fracture types: transverse, spiral, compression, comminuted, segmental, greenstick
  • Fracture etiology: exceeding bone's force limit; traumatic (falls), overuse, or disease.
• Bone Deformities: Atypical structure deviations, congenital or acquired. Signs include pain, discomfort, and difficulty moving; often needing surgery or orthopedic devices.

Osteoporosis

• A disease characterized by decreased bone density/normal bone tissue
• Risk factors may include menopause, certain drugs, diseases, alcoholism.
• Symptoms often include "silent disease" (no pain until fracture, often of vertebrae, hip, or wrist).
• Diagnosis is via bone densitometry, and < -2.5 T-score indicates osteoporosis.
• Treatment may include dietary modifications for calcium intake, antiresorptives, bone-forming drugs, surgery (in some cases), and exercise.
• Exercise focus on endurance, strength and balance.

Bone Cancer

• Uncontrolled cell multiplication of abnormal bone cells
• Common types: osteosarcoma, chondrosarcoma, Ewing's sarcoma
• Symptoms often include severe pain and may lead to metastasis..
• Diagnosis frequently involves biopsy.
• Treatment may include surgery, chemotherapy, and radiation.

Stress Raisers

• Force divided by area subjected to force
• Common types: traction, compression, shear, torsion, bending/flexion; excessive force can lead to injury.

Hormone Stress

• Hormones influencing bone: Growth hormone, thyroid hormones, sex hormones (estrogen, progesterone, testosterone), insulin, IGFs, cortisol, parathyroid hormone, calcitonin
• Imbalance in these hormones can affect bone health.

Aging Effects on Bone

• Physiological processes, starting at conception, negatively affect bone mass and quality; increased fracture risks.
• Metabolic factors: decreased collagen quality; lower microfracture repair ability; increased bone resorption vs. formation. More bone breakdown than creation.

Histological Changes in Bone Tissue

• Relative loss of cancellous bone (compared to cortical bone), reduced number of trabeculae, increase in periosteum diameter to maintain mechanical integrity to fight microfractures, and decrease in angiogenesis, reduction in bone forming surfaces, decreasing of osteocalcin, shorter osteoblast cell half-life. and decreasing telomerase in somatic cells. These factors may impact proliferation and differentiation of blasts.

Oxidative Stress in Bone

• Imbalance in oxidizing/deoxidizing agents. Excessive ROS production damages cells, and inhibits action of osteogenic factors.

Additional Notes

• Specific points about the usefulness of certain interventions at different ages related to bone density/strength improvements are noted
• Bone remodeling, where bone is broken down and rebuilt, is a continuous process.
• Hormones, nutrition, and stress can influence the rate of bone remodeling.
• Bone quality and density decrease with age, and this can affect function.