Bob ZhengWuhan University1.Bone replacement is the replacement of old bone tissue by new bone tissueNever metabolically at restReplacing itself throughout adult life2.Remodeling allows worn or injured bone to be removed and replaced with new tissue3.Remodeling allows bone to serve as the bodys storage area for calciumConstant supply of Ca2+ in the blood stream needed for:Transmission of nerve impulsesMuscle contractionBlood coagulationCell division 4.Osteoclast and osteoblast5.Sufficient quantities of calcium(Ca) and phosphorus(P)6.Sufficient amounts of vitamins, particularly vitamin D7.Proper amounts of the hormonesGrowth hormone(GH), Calcitonin(CT), Parathormone(PTH), Sex hormones8.Secreted by the pituitary gland , responsible for general growth of bones Too much GigantismToo little Dwarfism9.CT is produced by the thyroid gland, inhibits osteoclastic activity PTH is secreted by the parathyroid glands, increases the number and activity of osteoclasts AntagonisticAntagonistic CT PTH 10.Control of Bone DepositionControl of Bone ResorptionCa2+ controlled by negative feedback loop11.Promote the growth of new boneBring about the degeneration of cartilage cells12.Aging for skeletal syetem happens when Osteoblast activity declines, while osteoclast activity remains level Loss of calcium from bones13.For female, this loss begins after age 40 but for male , this loss typically does not begin until after 6014.MENOPAUSE! Remember, estrogen(sex hormone for female) stimulates osteoblast activity and synthesis of bone matrix Men continue to produce androgens (sex hormone for male) into late life and thus are not as affected.15.Another effect for aging is the decrease in the rate of protein formation Less organic matrix more inorganic matrix Bones become brittle and easy to fracture16.When the loss of bone mass compromises normal function a person is diagnosed with osteoporosis.17.Premature menopause Body build short women have less bone mass to begin withWeight thinner at greater riskSmoking decreases estrogen levelsLack of dietary calciumSedentary lifestyle decrease rate of absorptionDrugs alcohol, cortisone, tetracyclineNulliparity (never had children)Ancestry or Family history18.No smokingTake in more calciumDont sit all the dayBe careful when taking drugs19.20.