ch06 The Skeletal System Bone Tissue

The Skeletal System: Bone Tissue

1. Overview

  • Functions of Bone and Skeletal System

  • Structure of Bone

  • Histology of Bone Tissue

  • Blood and Nerve Supply of Bone

  • Bone Formation

  • Bone’s Role in Calcium Homeostasis

  • Exercise and Bone Tissue

  • Aging and Bone Tissue

2. Functions of Bone and Skeletal System

2.1 Support

  • Provides structural framework for the body

  • Supports soft tissues

  • Offers attachment points for tendons of skeletal muscle

2.2 Protection

  • Protects vital internal organs:

    • Cranium: protects brain

    • Vertebrae: protects spinal cord

    • Ribs: protect lungs and heart

2.3 Assistance in Movement

  • Skeletal muscles attach to bones

  • Muscle contraction pulls on bones, enabling movement

2.4 Mineral Homeostasis

  • Bone tissue stores essential minerals

  • Major reservoir for critical minerals:

    • Calcium (99% of body’s content)

    • Phosphorus

2.5 Blood Cell Production

  • Red bone marrow produces:

    • Red blood cells

    • White blood cells

    • Platelets (process called hemopoiesis)

2.6 Triglyceride Storage

  • Yellow bone marrow stores triglycerides in adipose cells

  • Serves as a potential chemical energy reserve

3. Structure of Bone

  • Major components of long bones:

    • Diaphysis: shaft of the bone

    • Epiphysis: ends of the bone

    • Metaphysis: region where diaphysis meets epiphysis (epiphyseal growth plate)

    • Articular cartilage: covers joint surfaces

    • Perforating fibers: attach periosteum to bone

    • Medullary cavity: hollow interior of the bone

    • Endosteum: lining of the medullary cavity

4. Histology of Bone Tissue

4.1 Extracellular Matrix

  • Composed of:

    • 25% water

    • 25% collagen fibers

    • 50% crystallized mineral salts (primarily calcium phosphate)

4.2 Calcification Process

  • Initiated by bone-building cells called osteoblasts

  • Mineral salts deposited and crystallize in collagen framework

  • Flexibility of bone relies on collagen fibers

4.3 Types of Bone Cells

  • Osteogenic cells: divide and develop into osteoblasts

  • Osteoblasts: synthesize extracellular matrix

  • Osteocytes: mature bone cells, maintain bone health

  • Osteoclasts: break down bone matrix to regulate calcium levels

4.4 Types of Bone Tissue

  • Compact Bone:

    • Resists stresses from weight and movement

    • Arranged in structural units called osteons (Haversian systems)

  • Spongy Bone:

    • Lacks osteons, arranged in trabeculae

    • Supports and protects red bone marrow

5. Bone Formation

  • Ossification: process of bone formation

  • Occurs in four situations:

    1. Formation in embryos

    2. Growth until adulthood

    3. Remodeling

    4. Repair of fractures

5.1 Types of Ossification

  • Intramembranous ossification: forms flat bones (skull, mandible)

  • Endochondral ossification: replaces cartilage with bone (most bones)

6. Bone Growth

6.1 Growth in Length

  • Involves:

    1. Growth of cartilage at epiphyseal plate

    2. Replacement of cartilage with bone

6.2 Growth in Thickness

  • Occurs through remodeling at the outer surface

7. Factors Affecting Bone Growth and Remodeling

7.1 Minerals and Vitamins

  • Essential for metabolism and remodeling include:

    • Calcium, phosphorus, magnesium, fluoride, manganese

    • Vitamins A (osteoblast activity), C (collagen synthesis), D (calcium absorption)

7.2 Hormones

  • Growth factors (IGFs), thyroid hormones, insulin support bone growth

  • Sex hormones (estrogen, testosterone) lead to growth spurts and influence structural changes

8. Fracture and Repair of Bone

8.1 Types of Fractures

  • Open (compound), Closed (simple), Comminuted, Greenstick, Impacted, Pott’s, Colles’, and Stress fractures

8.2 Repair Process

  • Steps of Repair:

    1. Formation of fracture hematoma

    2. Fibrocartilaginous callus formation

    3. Bony callus formation

    4. Bone remodeling

9. Bone’s Role in Calcium Homeostasis

  • Bone regulates blood calcium levels through:

    • Parathyroid hormone (PTH): increases blood calcium by stimulating osteoclasts

    • Calcitriol: promotes intestinal absorption of calcium

    • Calcitonin: inhibits osteoclast activity, lowering blood calcium levels

10. Exercise and Bone Tissue

  • Mechanical stress increases bone strength through mineral deposition and collagen production

  • Weight-bearing activities are crucial for building and maintaining bone mass

11. Aging and Bone Tissue

  • Decrease in sex hormones leads to loss of bone mass

  • Aging causes:

    1. Loss of bone mass (osteoporosis)

    2. Increased brittleness due to decreased collagen production

12. Summary

  • The skeletal system features complex interactions between various cellular processes, hormones, and mechanical stresses, all contributing to bone health and function.