Detailed Study Notes on Bone Histology and Physiology

BONE HISTOLOGY

  • Bone Matrix Composition

    • The matrix is composed of:

    • Calcium carbonate

    • Calcium phosphate

    • Primarily hydroxyapatite, which is the primary salt that makes bone hard.

    • The matrix is deposited in a framework of collagen fibers through a process called calcification or mineralization.

    • Functions:

    • Salts confer hardness to the bone.

    • Collagen fibers provide tensile strength.

    • Matrix composition proportions:

    • 25% water

    • 25% protein fibers

    • 50% minerals

COMPACT BONE

  • Definition and Characteristics

    • Bone can be classified as compact or spongy.

    • Compact bone is dense bone tissue which consists of structural units known as osteons (Haversian systems).

    • Features of Osteons:

    • Cylinders of tissue formed from concentric layers known as lamellae.

    • A central canal that holds a blood vessel (Haversian canal).

    • Osteocytes connected to each other and to the central canal via tiny canals called canaliculi.

SPONGY BONE

  • Structure and Function

    • Spongy bone appears to have a sponge-like form due to trabeculae, which are thin rods and plates of bone.

    • Characteristics:

    • Spaces between trabeculae are filled with red bone marrow.

    • Provides structural strength with minimal weight, as trabeculae form along the lines of stress on the bone.

    • Contains fewer osteons than compact bone, leading to its classification as cancellous bone.

BONE HOMEOSTASIS

  • Remodeling Process

    • Bone remodeling involves the replacement of old bone tissue with new tissue.

    • The process includes:

    • Osteoclasts: Cells that destroy old bone (characterized by a clubbed appearance).

    • Osteoblasts: Cells that construct new bone (play a role in building bone).

    • The balance between osteoclast and osteoblast activities affects bone mass:

    • An increased osteoclast activity with decreased osteoblast activity leads to bone loss.

    • Conversely, an increased osteoblast activity with decreased osteoclast activity leads to bone creation.

TYPES OF FRACTURES

  • General Definition

    • Upon physical trauma or other conditions, bones can fracture, classified as follows:

    • Stress Fracture:

      • Caused by abnormal stress or trauma to a bone, such as from car accidents, falls, or athletics.

    • Pathological Fracture:

      • Occurs in bones weakened by diseases such as bone cancer or osteoporosis.

  • Specific Types of Bone Fractures:

    • Open fracture

    • Displaced fracture

    • Greenstick fracture

    • Comminuted fracture

    • Linear fracture

    • Transverse nondisplaced fracture

    • Oblique nondisplaced fracture

    • Spiral fracture

    • Colles fracture

    • Pott fracture

EXERCISE AND BONE HEALTH

  • Impact of Mechanical Stress

    • The response of bones to mechanical stress is crucial for maintaining bone health:

    • Increased mechanical stress leads to increased deposition of mineral salts and production of collagen fibers, which can help avoid osteoporosis.

    • Removal or decrease in mechanical stress results in bone weakening due to demineralization.

    • Weight-bearing activities: Essential for building and retaining bone mass throughout life.