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Bone H & R
Bone Homeostasis and Remodeling
| Question | Answer |
|---|---|
| Bone is what type of tissue? | Dynamic and active |
| How much of the skeleton is replaced by remodeling each year? | Five to ten percent |
| How much calcium may leave or enter the adult skeleton each year? | One- half gram of calcium |
| How often is spongy bone replaced? | Three to four years |
| How often is compact bone is replaced? | Ten years |
| What is bone remodeling? | Deposit and resorption |
| What is bone resorption? | Osteoclasts break down bone matrix with lysosomal enzymes and hydrochloric acid |
| What do lysosomal enzymes do in bone resorption? | Digests organic matrix |
| What does hydrochloric acid do in bone resorption? | Converts calcium salts to a soluble form |
| What do osteoclasts do in bone resorption? | Osteoclasts phagocytize demineralized matrix and dead osteocytes |
| What do osteoblasts do in bone deposition? | Osteoblasts deposit the new bone matrix |
| What are the two reasons for bone deposition? | To repair injury or to add strength |
| What do equal depositing and resorption do? | Maintain mass |
| What is required for optimal bone bone deposition? | A healthy diet of protein, vitamins C, D, A and minerals Ca, P, Mg, Mn |
| What is remodeling regulated by? | Two control loops that serve different purposes |
| What is the negative feedback loop with hormones that regulates bone remodeling? | Maintaining calcium homeostasis |
| What is the response to mechanical and gravitational stress in bone remodeling? | Keeping bone strong |
| Why is bone remodeling controlled by hormones? | To maintain calcium ion levels in blood |
| What is PTH? | Parathyroid hormone |
| What is calcitonin? | Thyroid gland |
| What is the calcium homeostasis of blood? | 9-11 mg/ 100 mL |
| What does low blood calcium stimulate? | The release of PTH which causes osteoclasts to resort bone (releases calcium in blood) |
| What does high blood calcium stimulate? | The release of calcitonin which causes calcium salts to be deposited |
| What is hypercalcimia? | High levels of calcium cause organs to harden |
| What are the two types of mechanical stress on bones? | Muscle pull and gravity |
| What is Wolf’s Law? | Bone grows or remodels in response to stress and demand |
| What is the first observation of Wolf’s Law? | Long bones are thickest in mid-diaphysis (most stress) |
| What is the second observation of Wolf’s Law? | Curved bones are thickest near the buckle point |
| What is the third observation of Wolf’s Law? | Trabeculae of spongy bone form trusses along compression lines |
| What is the fourth observation of Wolf’s Law? | Large, bony projections occur where heavy, active muscles attach |
| What is the fifth observation of Wolf’s Law? | Handedness; bones of one upper limb is thicker than the less used limb |
| Who are two types of individuals who have no projections on their bones? | Unborn children and bedridden individuals |
| Why do fetal bones and those found in bedridden bones have no projections? | They muscles in these individuals are weaker an |
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