Human Skeleton Development

Skeletal Cartilage

• Made of highly resilient, molded cartilage tissue that consists primarily of water
• Contains no blood vessels or nerves
• Surrounded by perichondrium, a layer of dense connective tissue that helps resist outward expansion and contains blood vessels for nutrient delivery

Types of Cartilage

• Hyaline cartilage:
  • Provides support, flexibility, and resilience
  • Most abundant type; contains collagen fibers only
  • Found in articular (joints), costal (ribs), respiratory (larynx), and nasal cartilage (nose tip)
• Elastic cartilage:
  • Similar to hyaline cartilage, but contains elastic fibers
  • Found in external ear and epiglottis
• Fibrocartilage:
  • Thick collagen fibers; has great tensile strength
  • Found in menisci of knee and vertebral discs

Cartilage Growth

• Appositional growth:
  • Cartilage-forming cells in perichondrium secrete matrix against external face of existing cartilage
  • New matrix laid down on surface of cartilage
• Interstitial growth:
  • Chondrocytes within lacunae divide and secrete new matrix, expanding cartilage from within
  • New matrix made within cartilage

Functions of Bones

• Support for body and soft organs
• Protection for brain, spinal cord, and vital organs
• Movement (levers for muscle action)
• Mineral and growth factor storage
• Blood cell formation (hematopoiesis)
• Triglyceride (fat) storage
• Hormone production (osteocalcin regulates insulin secretion, glucose levels, and metabolism)

Classification of Bones

• 206 named bones in human skeleton
• Divided into two groups based on location:
  • Axial skeleton (skull, vertebral column, rib cage)
  • Appendicular skeleton (bones of upper and lower limbs, girdles attaching limbs to axial skeleton)
• Classified according to shape:
  • Long bones
  • Short bones
  • Flat bones
  • Irregular bones

Bone Structure

• Bones are organs composed of different types of tissues (bone, nervous, cartilage, fibrous connective, muscle, and epithelial)
• Three levels of structure: gross, microscopic, and chemical
• Compact and spongy bone:
  • Compact bone: dense outer layer on every bone that appears smooth and solid
  • Spongy bone: made up of a honeycomb of small, needle-like or flat pieces of bone called trabeculae
• Structure of short, irregular, and flat bones:
  • Consist of thin plates of spongy bone (diploe) covered by compact bone
  • Compact bone sandwiched between connective tissue membranes
• Structure of typical long bone:
  • Diaphysis (shaft), epiphyses (bone ends), and membranes