1. Bone Formation, Growth and Remodeling

2. Bone formation The Skeleton is formed from two of the strongest and most supportive tissues in the body: Cartilage and bone In embryo: the skeleton is primarily make of hyaline cartilage In young child: most of the cartilage has been replaced by bone

3. Bone formation Except for flat bones, which form on fibrous membranes, most bones develop using hyaline cartilage structure as their “models” Ossification: Bone formation Step 1. The hyaline cartilage model is completely covered with bone matrix by bone-forming cells called osteoblasts Step 2. The enclosed hyaline cartilage model is digested away, opening up a medullary cavity within the newly formed bone

4. Long bone growth The epiphyseal plates provide for longitudinal growth of the long bones during childhood:  “New” Cartilage is formed continuously on the external face of the articular cartilage and on the epiphyseal plate surface that is farther away from the medullary cavity  “Old” cartilage on the internal face of the articular cartilage and medullary cavity is broken down and replaced by bony matrix

5. Bone remodeling Bones are remodeled continually in response to changes in two factors: 1.Calcium levels in the blood (determines when to break down or form bones) 2.The pull of gravity and muscles on the skeleton (determines where to break down or form bones)

6. The Skeletal System Forming / Molding Bone: – Osteoblasts: Cells that rebuild your bones Create new bone cells Takes free floating Calcium and converts it into bone

7. The Skeletal System Forming / Molding Bone: – Osteoclasts: Cells that release calcium from the bone into the blood system Increase calcium in the blood Parathyroid Hormone (PTH) activates Osteoclasts

8. Simple Bone breaks cleanly, but does not penetrate the skin Sometimes called a “closed fracture”

9. Compound Broken ends of the bone protrude through soft tissues and the skin Sometimes called an “open fracture”

10. Communited Bone breaks into many fragments Particularly common in the aged, whose bone are more brittle

11. Spiral Ragged break occurs when excessive twisting forces are applied to a bone Common sports fracture

12. Greenstick Bone breaks incompletely, much in the way a green twig breaks

13. Compression/Depressed/Impacted Compression: Bone is crushed Depressed: Broken bone portion is pressed inward Impacted: Broken bone ends are forced into each other

14. Stages in the healing of a bone fracture 1. Blood vessels rupture. A blood filled swelling called a hematoma forms. Bone deprived of nutrition die. 2. Break is splinted. Growth of new capillaries. Disposal of dead tissue. 3. Fibrocartilage is replaced by spongy bone called a bony callus. 4. Bony callus is remodeled over the next few months in response to stress.