• found throughout the body
• surrounded by perichondrium
• consists primarily of water
• resilient (springs back to original shape)

1. Hyaline cartilage - most abundant; provides support through flexibility
2. Elastic cartilage - contains many elastic fibers; able to tolerate repeated bending
3. Fibrocartilage - an intermediate between hyaline and elastic

1. Appositional growth - chondroblasts in the surrounding perichondrium produce new cartilage
2. Interstitial growth - chondrocytes within cartilage divide and secrete new cartilage

1. Support
2. Movement
3. Protection
4. Mineral Storage
5. Blood-cell formation

1. Long bones - longer than wide; shaft plus ends (arm, leg)
2. Short bones - roughly cube-shaped (wrist, ankle)
3. Flat bones - thin and flattened, usually curved (sternum, ribs)
4. Irregular bones - various shapes, do not fit into other categories (vertebra)

• compact bone - dense outer layer of bones
• spongy (cancellous) bone - internal network of bones

• Diaphysis - shaft of bone
• Epiphysis - ends of bone
• Blood vessels
• Medullary cavity - hollow cavity filled with yellow marrow
• Membranes - periosteum (outer layer), perforating fibers, endosteum (inner layer)

• contain bone marrow but no marrow cavity
• Diploe: internal spongy bone of flat bones

• anatomy of a bone reflects stresses
• compression and tension greatest at external surfaces
• markings - projects for muscle attachment, surfaces that form joints, depressions and openings

• 35% organic components  (cells, fibers, collagen)
• 65% inorganic mineral salts (primarily calcium phosphate)

1. Ossification
2. Intramembranous Ossification
3. Endochondral Ossification

1. bone-tissue formation
2. bones formed directly from mesenchyme
3. bones form from hyaline cartilage

• cartilage is organized for quick, efficient, growth
• cartilage cells form tall stacks (chondroblasts at the top divide quickly)
• pushes the epiphysis away from the diaphysis
• lengthens entire long bone

Hormonal Regulation of Bone Growth

1. Growth Hormone - produced by the pituitary glane; stimulates epiphyseal plates
2. Thyroid Hormone - ensures that the skeleton retains proper proportions
3. Sex Hormones - estrogen and testosterone; promote bone growth and later indices closure of epiphyseal plates

• 500 mg of calcium may enter of leave the adult skeleton each day
• spongy (cancellous) bone is replaces every 3-4 years
• compact bone is replaced every 10 years

1. osteoblasts
2. osteoclasts

1. bone deposition, ADD bone tissue to the external surface of diaphysis (shaft)
2. bone reabsorption, REMOVE bone from the internal surface of the diaphysis (breaks down bone tissue by secreting HCl and lysosomal enzymes)

1. Comminuted - bone fragments into 3+ pieces
2. Compression - bone is crushed
3. Spiral - ragged break due to excessive twisting (sports injury)
4. Epiphyseal - epiphysis separates from diaphysis
5. Depressed - broken bone is pressed inward
6. Greenstick - bone breaks completely (like a twig snapping)

1. Osteoporosis - bone removal outpaces bone deposition
2. Paget's Disease - bone deposition outpaces bone removal
3. Osteomalacia - bones are inadequately mineralized (adults)
4. Rickets - same as osteomalacia (children)
5. Osteosarcoma - bone cancer