Skeletal System

• Skeletal system


  Includes bones and connective tissue like ligaments, tendons, and cartilage
• There are different kinds of skeletal systems in different organisms
• Skeletal systems in other organisms

  • Earthworms have a hydrostatic skeleton
  • Insects have an exoskeleton
  • Humans have an endoskeleton
• Functions of the skeletal system

  • Supports the body and protects organs
  • Stores important minerals
  • Produces red and white blood cells
  • Enables movement (with muscles)
• An adult human generally has 206 bones
• Axial skeleton


  Includes the bones in the skull, ears, throat, vertebral column, and ribcage
• Appendicular skeleton


  Includes the bones of the arms, shoulder girdle, legs, and pelvic girdle
• Types of bone shapes

  • Long bones
  • Short bones
  • Sesamoid bones
  • Flat bones
  • Irregular bones
• Long bones


  • Cylinder shaped, longer than wide, moved by muscle contraction
• Short bones


  • Cube shaped, length and width close to equal, offer stability
• Sesamoid bones


  • Roundish, handle pressure well (e.g. patella)
• Flat bones


  • Often curved and thin (e.g. skull bones, shoulder blades)
• Irregular bones


  • Irregular shape, protective from assorted forces (e.g. vertebrae)
• Compact bone tissue


  Hard outer layer
• Spongy bone tissue


  Inner layer containing bone marrow
• Yellow marrow


  Stores fat for long-term energy
• Red marrow


  Where blood cells are made (red blood cells, white blood cells, platelets)
• Bones are vascular with a rich blood supply
• Osteoblasts


  Cells that make bone
• Osteocytes


  Cells that maintain bone structure
• Osteoclasts


  Cells that break down bone structure using lysosomes and acids
• Bone remodeling occurs, with 5-10% of the skeleton remodeled each year
• Bones store calcium, which is important for muscle contraction and other body processes
• Chondroblasts


  Cells that make cartilage
• Chondrocytes


  Cells that maintain cartilage
• Bone growth


  1. Cartilage serves as a template, then bone replaces most of it

  2. Osteoblasts help bones grow in length until early adulthood

  3. Bones can also grow in diameter after length growth stops
• Bone fracture healing


  1. Fracture hematoma forms

  2. Internal and external calluses form from cartilage and bone

  3. Osteoclasts remove damaged bone

  4. Osteoblasts remodel the new bone
• Fractures can take 6-8 weeks or longer to heal depending on variables
• Severe fractures can cause fat embolism syndrome which requires emergency care
• Osteogenesis imperfecta


  Genetic disorder affecting collagen production, leading to brittle bones