Skeletal System

• Humans are vertebrates, animals having a vertebral column or backbone. They rely on a sturdy internal frame that is centered on a prominent spine. The human skeletal system consists of bones, cartilage, ligaments and tendons and accounts for about 20 percent of the body weight.

  
• Tendons

  Bones to muscles
• Ligaments

  Bones to bones

  
• Components of the skeletal system

  • Tendons
  • Ligaments
  • Bones
  • Joints
  • Cartilage

  
• Functions of the skeletal system

  • Providing support to the body
  • Storing minerals and lipids
  • Producing blood cells
  • Protecting internal organs
  • Allowing for movement

  
• Bones are considered as organs because they contain cells which then forms several different types of tissues such as nerves, blood tissue, cartilage and others besides bone.

  
• Osteoblasts

  Bone-forming cells that produce a new bone called "osteoid" which is made of bone collagen and other protein

  
• Osteoclasts


  Large cells that resorb or break down or dissolve the bone

  
• Osteocytes


  Mature bone cells inside the bone

  
• Osteogenic cells


  Undifferentiated with high mitotic activity found in periosteum and the endosteum, origin of osteoblast, osteoclast, and osteocytes
• Bone is not formed without destroying it

  
• Compact (Cortical) bone


  • Closely packed osteons or Haversian systems to form a solid mass
  • Found in the middle of long bones to support body weight

  
• Haversian canal system


  • Osteon - smallest unit of bone tissue
  • Haversian canal - houses blood vessels and nerves
  • Lacunae - chambers housing the cells (osteocytes)
  • Canaliculi - connects lacunae and osteocytes
• Spongy (Cancellous) bone


  • Lighter and less dense than compact bone
  • Consists of trabeculae (plates) and bars of bone adjacent to small, irregular cavities that contain red bone marrow
  • Canaliculi connect to the adjacent cavities, instead of a central haversian canal, to receive their blood supply

  
• Types of bones


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

  
• Flat bones


  Somewhat flattened, can provide protection and large areas of attachment for muscles

  
• Long bones


  Longer than they are wide, function to support the weight of the body and facilitate movement, consist of a long shaft with two bulky ends or extremities

  
• Short bones


  Cube-shaped about as long as they are wide, provide stability and some movement, consist primarily of spongy bone

  
• Irregular bones


  Vary in shape and structure, often have a fairly complex shape to help protect internal organs, primarily spongy bones covered with a thin layer of compact bone

  
• Sesamoid bone


  Small nodular bone most often present embedded in tendons, acts like pulleys to provide a smooth surface for tendons to slide over, increases the tendon's ability to transmit muscular forces

  
• Sesamoiditis


  Inflammation of the sesamoid bones, usually caused by increased pressure or loading on the sesamoid bones and associated tendons

  
• Diaphysis


  Tubular shaft that runs between the proximal and distal ends of a long bone, walls are composed of dense and hard compact bone, contains the medullary cavity filled with yellow marrow

  
• Epiphysis


  Wider section at each end of a long bone, filled with spongy bone, red marrow fills the spaces in the spongy bone

  
• Epiphyseal plate (growth plate)


  Layer of hyaline cartilage in a growing bone, disappears when the bone stops growing in early adulthood

  
• Parts of a long bone

  • Diaphysis
  • Epiphysis

  
• Diaphysis


  The tubular shaft that runs between the proximal and distal ends of the bone

  
• Medullary Cavity


  The hollow region in the diaphysis filled with yellow marrow
• Walls of the diaphysis


  • Composed of dense and hard compact bone

  
• Epiphysis


  The wider section at each end of the bone filled with spongy bone

  
• Metaphysis


  The narrow area that contains the epiphyseal plate
• Epiphyseal plate (growth plate)


  A layer of hyaline cartilage in a growing bone

  
• Epiphyseal line


  Formed when the epiphyseal plate is replaced by osseous tissue as the bone stops growing

  
• Endosteum


  A membranous lining of the medullary cavity, where bone growth, repair, and remodeling occur

  
• Periosteum


  A fibrous membrane covering the entire outer surface of the bone except where the epiphyses meet other bones to form joints

  
• Articular cartilage


  A thin layer of cartilage covering the epiphysis that reduces friction and acts as a shock absorber
• In adults, the red bone marrow is only found at the ends of the bones

  
• Articular Cartilage is white at the ends of the bones

  
• Arthritis


  Caused by the wearing down of the articular cartilage, leading to damage to the joints
• Types of Bone Marrow

  • Red Marrow (blood)
  • Yellow Marrow (fat)
• Hematopoiesis


  1. Blood cell formation happens in the red bone marrow in the epiphysis

  2. Babies are born with only red bone marrow, which is replaced by yellow marrow over time due to a decrease in erythropoietin

  3. By adulthood, the amount of red marrow has halved, and this reduces further to around 30% in older age