Bones and Skeletal Tissues

Bones and Skeletal Tissues

Overview of the Chapter

• Bones and Cartilages: Form the internal support of the body.
• Key Topics Covered:
  • 6.1 Skeletal cartilages
  • 6.2 Functions of bones
  • 6.3 Classification of bones
  • 6.4 Bone structure
  • 6.5 Development of bones
  • 6.6 Remodeling of bones
  • 6.7 Repair of bones
  • 6.8 Developmental aspects of bones

6.1 Skeletal Cartilages

• Types of Cartilage:
  • Hyaline: Most abundant, flexibility, and support (e.g., coastal cartilage, articular cartilage).
  • Elastic: Contains elastic fibers for structural support (e.g., external ear).
  • Fibrocartilage: Composed of thick collagen fibers, provides tensile strength (e.g., menisci of knee, intervertebral discs).
• Structure: Composed of chondrocytes in a jelly-like extracellular matrix.

6.2 Functions of Bones

• Major Functions:
  1. Support: Maintains body shape and structural framework.
  2. Protection: Shields vital organs (e.g., brain, heart).
  3. Movement: Functions as levers for muscle actions.
  4. Mineral Storage: Reservoir for crucial minerals (e.g., calcium, phosphorus).
  5. Hematopoiesis: Blood cell formation occurs in red marrow.
  6. Triglyceride Storage: Fat storage in bone cavities for energy.
  7. Hormone Production: Bones secrete osteocalcin, regulating insulin secretion and metabolic processes.

6.3 Classification of Bones

• Bone Groups:
  • Axial Skeleton: Skull, vertebral column, rib cage.
  • Appendicular Skeleton: Upper and lower limb bones, girdles.
• Bone Shapes:
  • Long: Longer than wide (e.g., femur).
  • Short: Cube-shaped (e.g., carpals).
  • Flat: Thin and slightly curved (e.g., sternum).
  • Irregular: Various shapes (e.g., vertebrae).

6.4 Bone Structure

• General Structure:
  • Compact Bone: Dense outer layer, smooth appearance.
  • Spongy Bone: Honeycomb structure with trabeculae, open spaces filled with marrow.
• Bone Markings:
  • Projections, Depressions, Openings: Sites for muscle attachment, joint formation, and passageways for blood vessels/nerves.

6.5 Bone Development

• Ossification: The formation of bone tissue, starting in the 2nd month of pregnancy.
• Types of Ossification:
  • Endochondral: Cartilage replaced by bone; most of the skeleton.
  • Intramembranous: Bone formed from fibrous membranes; certain skull bones.

6.6 Bone Remodeling

• Process Overview: Continuous cycle of bone deposition and resorption, regulated by hormonal controls and mechanical stress.
• Bone Mass Recycling: 5-7% of bone mass is recycled weekly.

6.7 Bone Repair

• Fractures: Breaks in the bone, commonly due to trauma or bone thinning in elderly.
• Classification of Fractures:
  • Position of bone ends: Displaced or non-displaced.
  • Completeness of break: Complete or incomplete.
  • Skin penetration: Open (compound) or closed (simple).
• Healing Stages: Hematoma forms, followed by callus formation, and eventually remodeling.

6.8 Bone Disorders

• Common Disorders:
  1. Osteomalacia/Rickets: Poorly mineralized bones due to vitamin D deficiency.
  2. Osteoporosis: Bone resorption exceeds deposition, leading to weak bones.
  3. Paget’s Disease: Unbalanced bone deposition and resorption, leading to deformed bones.
• Risk Factors for Osteoporosis: Age, gender (postmenopausal women), lack of calcium & protein, lack of exercise, and smoking.
• Treatments: Calcium/vitamin D supplements, weight-bearing exercises, hormone replacement therapy, and medications to decrease osteoclast activity.