Bones: Structure and Function

Classification and Functions of Bones

Bones are classified based on their shape and structure, and they serve multiple functions in the human body, including support, protection, movement, mineral storage, and blood cell formation.

• Gross Anatomy: Bones are categorized as compact or spongy based on their density and structure.

• Long Bone Structure: Long bones consist of a shaft (diaphysis), two ends (epiphyses), and membranes (periosteum and endosteum).

• Microscopic Anatomy: Compact bone contains osteons (Haversian systems), while spongy bone contains trabeculae.

• Bone Markings: Surface features of bones include projections, depressions, and openings that serve as sites for muscle attachment or passage of nerves and blood vessels.

Chemical Composition of Bone

Bones are composed of organic components (cells and osteoid) and inorganic components (hydroxyapatite crystals).

• Organic: Collagen fibers provide flexibility and tensile strength.

• Inorganic: Calcium phosphate crystals provide hardness and resistance to compression.

Bone Growth and Remodeling

Bones grow in length and width through endochondral and intramembranous ossification. Remodeling is a lifelong process involving bone resorption and formation.

• Epiphyseal Plate: Growth in length occurs at the epiphyseal plate in long bones.

• Hormonal Regulation: Growth hormone, sex hormones, and other factors regulate bone growth and remodeling.

• Bone Repair: Healing of bone fractures involves hematoma formation, fibrocartilaginous callus formation, bony callus formation, and bone remodeling.

Additional info: The notes specify not to study leptin and serotonin's effects, mechanical stress-Wolf's law, or developmental aspects of bones.

Bone Diseases

• Osteoporosis: A condition characterized by decreased bone mass and increased fracture risk.

• Paget's Disease: Disorganized bone remodeling leading to structurally weak bone.

Additional info: Drug-induced osteoporosis and developmental aspects are excluded from study.

The Skeleton

Axial and Appendicular Skeleton

The human skeleton is divided into axial and appendicular components, each with distinct bones and functions.

• Axial Skeleton: Includes the skull, vertebral column, and thoracic cage.

• Appendicular Skeleton: Includes the pectoral girdle, upper limbs, pelvic girdle, and lower limbs.

Vertebral Column

• Regions: Cervical, thoracic, lumbar, sacral, and coccygeal.

• Curvatures: Primary (thoracic and sacral) and secondary (cervical and lumbar).

• Abnormal Curvatures: Scoliosis (lateral curvature), kyphosis (excessive thoracic curvature), lordosis (excessive lumbar curvature).

Thoracic Cage

• Components: Sternum, ribs, and thoracic vertebrae.

• Function: Protects vital organs and supports upper limbs.

Appendicular Skeleton

• Pectoral Girdle: Clavicle and scapula.

• Upper Limb: Humerus, radius, ulna, carpals, metacarpals, phalanges.

• Pelvic Girdle: Hip bones (ilium, ischium, pubis).

• Lower Limb: Femur, tibia, fibula, tarsals, metatarsals, phalanges.

Additional info: Do not study arches of foot or developmental aspects.

Joints

Classification of Joints

Joints, or articulations, are classified based on their structure and function.

• Structural Classification:

  • Fibrous Joints: Bones joined by dense connective tissue; mostly immovable (e.g., sutures).

  • Cartilaginous Joints: Bones joined by cartilage; slightly movable (e.g., symphysis).

  • Synovial Joints: Bones separated by a fluid-filled joint cavity; freely movable.

• Functional Classification:

  • Synarthroses: Immovable joints.

  • Amphiarthroses: Slightly movable joints.

  • Diarthroses: Freely movable joints.

Synovial Joints

Synovial joints are characterized by a joint cavity containing synovial fluid, articular cartilage, and a joint capsule.

• Examples: Shoulder, elbow, hip, knee, ankle.

• Movements: Flexion, extension, abduction, adduction, rotation, circumduction.

Ligaments and Menisci

Ligaments connect bone to bone and stabilize joints. Menisci are fibrocartilaginous pads that improve joint fit and absorb shock.

• Shoulder Joint: Glenoid labrum, glenohumeral ligaments.

• Knee Joint: Menisci, cruciate ligaments (ACL, PCL), collateral ligaments.

• Hip Joint: Acetabular labrum, ligaments of femoral head.

Types of Synovial Joints and Movements

Synovial joints are classified by the shapes of their articulating surfaces and the movements they allow.

Inflammatory and Degenerative Joint Conditions

• Bursitis: Inflammation of bursae.

• Tendinitis: Inflammation of tendons.

• Arthritis: Includes osteoarthritis, rheumatoid arthritis, and gout.

Additional info: Do not study temporomandibular joint (TMJ) or developmental aspects.

Key Terms and Definitions

• Osteon: The structural unit of compact bone.

• Epiphyseal Plate: Growth plate in long bones.

• Meniscus: Crescent-shaped fibrocartilage in the knee joint.

• Synovial Fluid: Lubricating fluid in synovial joints.

• Ligament: Connective tissue joining bone to bone.

Formulas and Equations

• Bone Mass Equation:

• Wolff's Law (excluded from study): Bone adapts to the loads under which it is placed.