Bones Structure, Remodeling, Homeostatic Imbalances

Classification of Bones Long: longer than wide Short: roughly cube- shaped Flat: flat and slightly curved Irregular: everything else

Bone is always changing Fetus skeleton is a cartilage template, replaced by bone Ossification (bone formation) continues until about age 16 in females and 21 in males Long bones stop growing in length when the epiphyseal plate ossifies

Fetal Skeleton

Cartilage is replaced by bone

Longitudinal vs Appositional growth

Bones continue to change or remodel because of: Hormones: growth and sex Stresses and gravity (femur is replaced every 6 months) Body’s need for calcium

Types of bone cells: Osteoblasts: Bone-forming cells that secrete matrix, then get trapped in it and turn into: Osteocytes: Mature bone cells imbedded in matrix of flexible collagen and hydroxyapatite (Ca salt)

Bone remodels due to osteoblasts and osteoclasts Osteoclasts: Bone destroying cells, secrete enzymes that destroy matrix and break down calcium for the blood Osteoclasts: Bone destroying cells, secrete enzymes that destroy matrix and break down calcium for the blood

Balancing blood calcium

Bone Fractures A break in a bone Types of bone fractures –Closed (simple) fracture – break that does not penetrate the skin –Open (compound) fracture – broken bone penetrates through the skin Treatment: closed or open (surgery) reduction and immobilization (cast) –Reduction = Realignment of the bone

Types of Fractures

Repair of fractures Hematoma (blood-filled swelling) is formed Break is splinted by fibrocartilage to form a callus Fibrocartilage callus is replaced by a bony callus Bony callus is remodeled to form a permanent patch

Steps in healing of fractures

Bone Problems Osteoporosis: bone mass is lost resulting in porous bones that are easily broken, common in the elderly

Osteomalacia Softening of bones due to lack of calcium Called rickets in children

Paget’s Disease Abnormal growth and resorption of bone Possibly caused by a virus Mostly affects hips, shoulders and vertebrae

Spinal curvatures Scoliosis: lateral curvature Lordosis: “swayback”, common in pregnant women and “beer bellies” Kyphosis: “humpback”, common in osteoporosis

X ray of osteoporosis

X Ray Quiz