Chapter 6: Osseous Tissue and Bone Structure

Introduction to the Skeletal System

• Functions of the Skeletal System:
  • Support: Provides structural support for the entire body and a framework for soft tissues and organs attachment.
  • Protection: Surrounds and protects delicate tissues and organs (e.g., ribs protect heart/lungs, skull protects brain).
  • Leverage: Bones act as levers to change magnitude and direction of skeletal muscle forces.
  • Storage:
    • Minerals: Bones store calcium salts, maintaining calcium and phosphate ion concentrations.
    • Energy: Yellow bone marrow stores adipose tissue as an energy source.
  • Blood Cell Production: Hematopoiesis occurs in red bone marrow, producing red/white blood cells and platelets.

Divisions of the Skeleton

• Adult Skeleton: Approximately 206 bones.
  • Axial Skeleton: 80 bones including the skull, hyoid, sternum, rib cage, vertebral column, sacrum, coccyx.
  • Appendicular Skeleton: 126 bones including limbs, pectoral and pelvic girdles.

Classification of Bones

• Flat Bones: Thin, parallel surfaces; e.g., skull, sternum.
• Long Bones: Long, slender; e.g., femur.
• Short Bones: Boxy; e.g., carpals.
• Irregular Bones: Complex shapes; e.g., vertebrae.
• Sesamoid Bones: Small, flat; e.g., patella.

Bone Markings and Features

• Projections for Muscle/Ligament Attachment: Tuberosity, Crest, Trochanter, Line, Tubercle, Epicondyle, Spine.
• Depressions/Openings: Groove, Fissure, Foramen, Notch, Meatus, Sinus, Fossa.
• Joint Forming Projections: Head, Facet, Condyle, Ramus.

Anatomy of Long Bones

• Diaphysis: Tubular shaft of compact bone.
• Epiphysis: Ends of the bone, primarily spongy bone.
• Medullary Cavity: Contains bone marrow.
• Membranes: Periosteum (outer), Endosteum (inner).

Bone Cells

• Osteoblasts: Immature cells that build bone matrix.
• Osteocytes: Mature cells maintaining bone matrix.
• Osteogenic Cells: Stem cells forming osteoblasts.
• Osteoclasts: Cells that digest and recycle bone matrix.

Microscopic Anatomy

• Compact Bone: Osteons with central canals.
• Spongy Bone: Trabeculae with marrow.

Bone Formation and Growth

• Osteogenesis/Ossification: Bone formation during development.
  • Intramembranous Ossification: Forms flat bones (e.g., skull).
  • Endochondral Ossification: Uses cartilage model, most body bones.
• Growth:
  • Longitudinal (length): Hyaline cartilage elongates.
  • Appositional (width): Outer surface growth, medullary cavity enlarges.

Fractures and Bone Repair

• Fracture Types: Simple, compound, transverse, linear, displaced, non-displaced.
• Repair Process: Hematoma formation, fibrocartilage callus, bony callus, remodeling.

Calcium Homeostasis

• Remodeling: Balanced deposition and resorption.
• Hormonal Control:
  • Parathyroid Hormone (PTH): Increases blood calcium by stimulating osteoclasts.
  • Calcitonin: Lowers blood calcium by inhibiting osteoclasts.
• Skeleton Role: Provides calcium reserve and maintains ion balance.