Bone Classification

• Bones are categorized based on their shape:
  • Long bones: Have a shaft (diaphysis) and two ends (epiphyses); e.g., femur, humerus
  • Short bones: Roughly cube-shaped; e.g., carpals, tarsals
  • Flat bones: Thin, flattened, and usually curved; e.g., skull bones, ribs
  • Irregular bones: Complex shapes, don't fit into other categories; e.g., vertebrae, facial bones
  • Sesamoid bones: Small, round bones embedded within tendons; e.g., patella

Bone Remodeling

• Bone remodeling is a continuous process of bone resorption and deposition.
  • Resorption: The breakdown of bone tissue by osteoclasts. These cells secrete acids and enzymes that dissolve the bone matrix.
  • Deposition: The formation of new bone tissue by osteoblasts. These cells produce new bone matrix, which mineralizes over time.
• Factors affecting bone remodeling:
  • Hormones (e.g., parathyroid hormone, calcitonin, estrogen)
  • Mechanical stress: Weight-bearing activities stimulate bone deposition.
  • Nutrition: Adequate intake of calcium and vitamin D is crucial.
• Importance of bone remodeling:
  • Maintaining bone strength and density
  • Repairing micro-damage from stress
  • Adapting bone structure to changing mechanical loads
• Wolff's Law: Bone in a healthy individual will adapt its structure to the demands placed upon it.

Long Bone Structure

• A typical long bone has characteristic features:
  • Diaphysis: The long, tubular shaft, composed of compact bone surrounding a marrow cavity.
  • Epiphysis: The expanded ends of the bone, composed of spongy bone filled with red bone marrow (important for blood cell production).
  • Articular cartilage: Thin layer of hyaline cartilage covering the epiphysis where the bone articulates (meets) with another bone. This cartilage reduces friction and absorbs shock.
  • Periosteum: A tough fibrous membrane covering the outer surface of the bone, except at the articular cartilage. Contains blood vessels and nerves. Provides attachment for tendons and ligaments.
  • Medullary cavity: A hollow space within the diaphysis filled with bone marrow (yellow bone marrow in adults, red bone marrow in children).
  • Endosteum: Thin membrane lining the medullary cavity; contains osteoblasts and osteoclasts.
  • Nutrient foramina: Small openings in the bone through which blood vessels pass.
  • Epiphyseal plate (growth plate): A layer of hyaline cartilage in growing bones, responsible for lengthening the bone. It is replaced by bone during adulthood.

Skeletal Bones

• The human skeleton is composed of 206 bones.
• These bones are divided into axial and appendicular skeletons.
• Axial Skeleton:
  • Forms the central axis of the body.
  • Includes the skull, vertebral column, and rib cage.
  • Its function is primarily to support and protect vital organs.
• Appendicular Skeleton:
  • Forms the bony framework of the limbs and girdles (shoulder and pelvic).
  • Includes the bones of the arms, legs, hands, and feet.
  • Its major function is movement and support.
• Key functions of the skeletal system:
  • Support: Provides a framework for the body.
  • Protection: Protects vital organs (e.g., brain, heart, lungs).
  • Movement: Provides levers for muscle action.
  • Mineral storage: Stores calcium and phosphorus.
  • Blood cell formation: Red bone marrow produces red blood cells, white blood cells and platelets.