Chapter 6

• Cartilage


  Provides firm yet flexible support within certain structures
• Bones


  Dynamic structures that are the major storage site for calcium in the body
• Remodeling


  The process responsible for changes in bone shape, the adjustment of bone to stress, bone repair, and calcium ion regulation in the body fluids

  
• Bone remodeling


  1. New bone is deposited on the outer surface and growth occurs at the epiphyseal plate

  2. Bone is removed from the inner, medullary surface of the bone

  3. As the bone diameter increases, the thickness of the compact bone relative to the medullary cavity tends to remain fairly constant

  4. If the size of the medullary cavity did not also increase as bone size increased, the compact bone of the diaphysis would become thick and very heavy

  
• If too much bone is deposited

  The bones become thick or develop abnormal spurs, or projections, that can interfere with normal function

  
• If too little bone formation or too much bone removal, as occurs in osteoporosis


  The bones are weakened and made susceptible to fracture

  
• Bone repair - Hematoma


  1. A clot forms in the damaged area

  2. Two to three days after the injury, blood vessels and cells from surrounding tissues begin to invade the clot

  3. Some cells produce a fibrous network of connective tissue between the fractured bones, which holds the bone fragments together and fills the gap between them

  4. Other cells produce islets of cartilage in the fibrous network

  
• Callus


  The network of fibers and islets of cartilage between the two bone fragments

  
• Bone repair - Callus formation

  1. Osteoblasts enter the callus and begin forming spongy bone

  2. Spongy bone formation in the callus is usually complete 4–6 weeks after the injury

  3. Immobilization of the bone is critical up to this time because movement can refracture the delicate new matrix

  4. Subsequently, the spongy bone is slowly remodeled to form compact and spongy bone, and the repair is complete

  
• Not long ago, it was common practice to immobilize a bone completely for as long as 10 weeks

  
• If a bone is immobilized for as little as 2 weeks, the muscles associated with that bone may lose as much as half their strength

  
• Bone matrix is reabsorbed, and the strength of the bone decreases if a bone is completely immobilized and not subjected to the normal mechanical stresses that help it form

  
• Classification of bone fractures

  • Open fracture
  • Closed fracture
  • Complicated fracture
  • Incomplete fracture
  • Complete fracture
  • Comminuted fracture
  • Impacted fracture
  • Linear fractures
  • Transverse fractures
  • Spiral fractures
  • Oblique fractures
  • Dentate fractures
  • Stellate fractures

  
• Bone


  The major storage site for calcium in the body
• Balanced osteoblast and osteoclast


  The movements of calcium into and out of a bone are equal

  
• Calcium homeostasis


  Maintained by three hormones: Parathyroid hormone (PTH), Vitamin D, and Calcitonin
• How PTH increases blood calcium levels

  1. PTH indirectly stimulates osteoclasts to break down bone, which releases stored calcium into the blood

  2. PTH stimulates the kidney to take up calcium from the urine and return it to the blood

  3. PTH stimulates the formation of active vitamin D, which, in turn, promotes increased calcium absorption from the small intestine

  
• Osteomyelitis


  A bacterial infection in bone that prevents normal functioning of the bone-forming osteoblast

  
• Staphylococcus aureus


  An aggressive pathogen that is the causative organism of osteomyelitis, whose cell walls contain a certain cell marker that alters signaling dynamic
• How Staphylococcus aureus can infect bone


  1. The bacterium spreads to the bone through the bloodstream from another infected location in the body

  2. The bacterium penetrates the bone through an open wound on the skin

  3. The bacterium is introduced into a joint or bone during surgery

  
• The most common treatment for osteomyelitis is a 4- to 8-week course of antibiotics
• Foramen


  A hole in a bone that exists because some structure, such as a nerve or blood vessel, passes through the bone at that point

  
• Canal or meatus

  An elongated, tunnel-like passage through a bone
• Fossa

  A depression in a bone

  
• Tubercle


  A rounded projection on a bone

  
• Process


  A sharp projection from a bone

  
• Condyle


  A smooth, rounded end of a bone, where it forms a joint with another bone