Bone as Leverage in the Body

• Bone is characterized as living, dynamic tissue, rather than inactive material, due to continuous cellular processes.
• Constant loading and unloading of calcium occurs in the skeleton, maintaining homeostatic levels in the blood.
• Importance of calcium:
  • When blood calcium levels are low, calcium is extracted from the bones.
  • Bones function as excellent storage sites for excess calcium.
• Peak bone density:
  • Women reach peak bone density around ages 20-25.
  • Men achieve peak bone density slightly later.
  • Building strong and dense bones is vital to prevent conditions such as osteoporosis, which leads to brittle bones and is associated with higher risk of fractures, especially from falls.

Osteoporosis and Fractures

• Osteoporosis results in bone loss, leading to increased fracture risk.
• Debate exists on the cause of hip fractures:
  • Whether the fracture leads to a fall or a fall leads to a fracture.
• Weight-bearing activities, especially walking up and down stairs, pose significant challenges as they radically change load on the hips.

Nutrients Stored in Bone

• Bones also serve as storage sites for:
  • Magnesium
  • Phosphorus
  • Lipids (fats stored in bone marrow for energy)

Blood Cell Production

• Bones are essential for blood cell generation:
  • Red blood cells
  • White blood cells
  • Platelets
• Blood cells are produced in the medullary cavity of bones.

Structure and Functions of Bones

• Bones act as levers, providing leverage when muscles contract.
• Features of bones:
  • Locations for attachment of tendons, ligaments, and aponeurosis (broad connective tissue)

Connective Tissues and Muscle Attachments

• Aponeurosis: A broad connective tissue that connects muscles to the skeleton, allowing the distribution of force across a wider area than tendons.
• Example: Latissimus dorsi muscle:
  • Has a tendon that attaches to the humerus and a wide area of aponeurosis to which it connects on the opposite side to the lumbar vertebrae and pelvis.

Classification of Bones

• Bones are classified by shape and structure:
  • Ossias: Refers to bones (os = bone in Latin).
  • Prefixes related to bone include terms like osteopath.

Types of Bone

• Major classifications include:
  • Long Bones: Cylindrical shape (e.g., femur, humerus).
  • Short Bones: Cuboidal shape, found in the wrists and hands (e.g., carpal bones).
  • Example: Eight small cuboidal bones in the wrist.
  • Flat Bones: Thin, flattened shape (e.g., bones of the skull).
  • Formed through intramembranous ossification.
  • Irregular Bones: Complex shapes that do not fit other classifications (e.g., vertebrae).
  • Sesamoid Bones: Bones that develop within tendons (e.g., kneecap/patella).

Development of Sesamoid Bones

• Patella: Develops in the quadriceps tendon, present at birth, but grows larger as the child crawls and bears weight.
• Increases mechanical advantage for quadriceps muscle function, aiding in leg extension.

Bone Anatomy

• Epiphysis: Ends of long bones, involved in joint formation.
• Diaphysis: Central shaft of a long bone, where bone develops through ossification.
• Metaphysis: Region between epiphysis and diaphysis, crucial for bone growth (growth plate).
• Articular Cartilage: Covers joint surfaces, facilitates movement, lacks nerve supply, hence pain-free during activities until degeneration occurs.
• Medullary Cavity: Hollowed-out center of bone, stores fat and produces blood cells.

Bone Growth and Ossification

• Intramembranous Ossification: Occurs between membranes, creating flat bones.
• Endochondrial Ossification: Occurs from a hyaline cartilage model during fetal development, leading to long bone growth.
  • Primary Ossification Center: Initial site of ossification that grows towards epiphyses.
  • Secondary Ossification Center: Develops in the epiphysis, grows toward the diaphysis.

Changes During Growth

• Epiphyseal plate: Growth plate where new bone is formed until closure at maturity (around 25 years).
• Osteoblasts and osteoclasts play crucial roles in forming and breaking down bone as needed.
• Changes in the metaphysis over time reflect growth and maturation, particularly in children and adolescents.

Mechanisms of Bone Remodeling

• Osteogenic Cells: Stem cells that differentiate into osteoblasts for bone formation.
• Osteoblasts: Build bone by secreting calcium phosphate.
• Osteocytes: Mature bone cells that maintain bone tissue and control mineral content.
• Osteoclasts: Cells that break down bone, critical for calcium release into the bloodstream when needed.

Conclusion

• The synthesis and remodeling of bone are continued processes even into adulthood, influenced by physical activity and overall health throughout a person's life. Regular exercise, quality nutrition, and understanding growth patterns shape the integrity of our bones.