Chapter 6 - The Skeletal System: Bone Tissue

Chapter 6 - The Skeletal System: Bone Tissue

Functions of Bone and the Skeletal System

  • Six Main Functions of the Skeletal System:

    1. Support: Provides a framework for the body, supporting soft tissues and providing attachment points for muscles.

    2. Protection: Encloses vital organs (e.g., skull protects the brain, ribcage protects the heart and lungs).

    3. Movement: Facilitates movement by acting as levers that muscles pull on.

    4. Mineral Storage: Serves as a reservoir for minerals such as calcium and phosphorus.

    5. Blood Cell Production (Hemopoiesis): Houses bone marrow where blood cells are produced.

    6. Energy Storage: Stores lipids in adipocytes within the yellow bone marrow.

Structure of Bone

  • Structure and Functions of Each Part of a Long Bone:

    • Diaphysis (shaft): Provides leverage and support.

    • Epiphyses (ends): Forms joints and contains spongy bone for energy storage and blood cell production.

    • Metaphysis: The region between the diaphysis and epiphysis where growth occurs.

    • Articular Cartilage: Smooth tissue covering the epiphyses, reducing friction in joints.

    • Periosteum: Dense layer of connective tissue enveloping the bone except at surfaces of joints; important for growth and repair.

    • Endosteum: Thin tissue lining the medullary cavity, involved in bone growth and remodeling.

Histology of Bone Tissue

  • Classification of Bone Tissue as Connective Tissue:

    • Bone tissue is classified as a connective tissue due to its composition of cells, fibers, and ground substance that work together to support and bind other tissues.

  • Components of Extracellular Matrix:

    • Comprises organic components (collagen fibers, ground substance) and inorganic components (hydroxyapatite crystals contributing to bone hardness).

  • Cellular Composition of Bone Tissue:

    • Osteoblasts: Cells responsible for bone formation.

    • Osteocytes: Mature bone cells that maintain the bone matrix.

    • Osteoclasts: Cells that break down bone tissue during remodeling.

    • Bone Lining Cells: Flat cells that line bone surfaces; regulate the passage of calcium and phosphate ions.

  • Comparison between Compact and Spongy Bone Tissue:

    • Compact Bone: Dense, forms the outer layer of bones, provides strength. Has structural units called osteons.

    • Osteon Structure: Composed of rings of lamellae surrounding a central canal (Haversian canal, which contains blood vessels and nerves).

    • Spongy Bone: Lattice-like structure, found mainly at the ends of long bones and within flat bones, supports weight and allows for flexibility. Composed of trabeculae (thin rods or plates of bone).

Blood and Nerve Supply of Bone

  • Blood Supply of Bone:

    • Supplied by nutrient arteries and veins, along with smaller vessels that enter through the periosteum.

    • Nerve Supply of Bone: Involves sympathetic nerves, responsible for providing sensory innervation and regulating blood flow.

Bone Formation

  • Steps of Intramembranous and Endochondral Ossification:

    1. Intramembranous Ossification: Simple formation directly from mesenchymal tissue (e.g., forming flat bones like the skull).

    2. Endochondral Ossification: Replacement of hyaline cartilage by bone, crucial for the formation of long bones and allows for growth in length.

  • Growth in Length and Thickness of Bone:

    • Length: Occurs at the epiphyseal plates through the process of chondrocyte proliferation and ossification.

    • Thickness: Involves appositional growth; osteoblasts in the periosteum add new bone to the outer surface while osteoclasts resorb bone from the inner surface.

  • Bone Remodeling Process:

    • Continuous turnover of bone tissue in response to mechanical stress, hormonal signaling, and repair processes. Involves bone resorption by osteoclasts and bone formation by osteoblasts.

Fracture and Repair of Bone

  • Common Types of Fractures:

    1. Simple Fracture: A break that does not penetrate the skin.

    2. Compound Fracture: A break that pierces the skin, increasing risk of infection.

    3. Greenstick Fracture: An incomplete fracture typically seen in children, where one side bends and the other side breaks.

    4. Comminuted Fracture: Bone shatters into many pieces.

  • Sequence of Events in Fracture Repair:

    1. Formation of a hematoma (blood clot).

    2. Fibrocartilaginous callus formation (soft callus formation).

    3. Bony callus formation (hard callus formation).

    4. Bone remodeling, where the bone regains its original shape.

Bone's Role in Calcium Homeostasis

  • Regulation of Blood Calcium Level:

    • Involves hormones such as parathyroid hormone (PTH) and calcitonin.

    • PTH increases blood calcium levels by stimulating osteoclast activity.

    • Calcitonin decreases blood calcium levels by inhibiting osteoclast activity.

  • Importance of Calcium in the Body:

    • Essential for muscle contraction, blood clotting, nerve transmission, and hormone secretion.

Exercise and Bone Tissue

  • Effect of Exercise and Mechanical Stress on Bone Tissue:

    • Mechanical stress from exercise stimulates bone formation and strengthens bone density. Weight-bearing exercises increase bone mass and counteract osteoporosis.

Disorders and Bone Tissue

  • Osteoporosis:

    • A disorder characterized by decreased bone density and quality, resulting in increased risk of fractures.

    • Commonly occurs in older adults, particularly postmenopausal women due to hormonal changes affecting calcium absorption and bone resorption.