Ch 6, 6 bone homeostasis Flashcards Preview

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Flashcards in Ch 6, 6 bone homeostasis Deck (11):

remodeling of bones

occurs throughout lifetime
a. in response to mechanical stress, damage and hormonal levels
b. variations in blood calcium levels


bone deposit

a. occurs where bone is injured or added strength is needed
b. requires a diet rich in protein; vitamin C, D and A; calcium; phosphorus, magnesium and manganese


bone resorption

occurs where there is a reduction in mechanical stress
increases with aging
a. Osteoclasts secrete
--lysosomal enzymes (digest organic matrix)
--acids (convert calcium salts into soluble forms)
b. dissolved matrix is transcytosed across osteoclast, enters interstitial fluid and then blood


control of remodelling

a. hormonal mechanisms that maintain calcium homeostasis in the blood-negative feedback loop
b. response to mechanical stress


hormonal control of blood calcium

a. blood calcium is necessary for..
-transmission of nerve impulse
-muscle contraction
-blood coagulation
-secretion by glands and nerve cells
-cell division

b. role of parathyroid hormone(PTH)
-decrease blood calcium
-parathyroids release PTH
-PTH stimulates osteoclasts to degrade bone matrix
-calcium released into blood
-increase in blood calcium
++if blood calcium is low, skeletal calcium is sacrificed tosatisfy other needs of the body


response to mechanical stress

a. a bone grows or remodels in response to forces or demands placed upon it
b. curved bones are thickest where they are most likely to buckle
c. trabeculae form along lines of stress
d. large, bony structures occur where heavy, active muscles attach


classification of bone fractures

1. position of bone ends after fracture
-non displaced-ends remain normal position
-displaced-ends out of normal alignment

2. completeness of break
-complete-broken all the way through
-incomplete-not broken all the way through

3. orientation of the break on the long axis of bone
-linear- parallel to the long axis
-transverse- perpendicular to long axis

4. whether or not the bone ends penetrate the skin
-compound (open)-bone ends penetratethe skin
-simple (closed) -bone ends do not penetrate the skin


stage 1; bone healing

hematoma forms
a. torn blood vessels hemorrhage
b. clot forms
c. site becomes swollen, painful and inflamed


stage 2

fibrocartilaginous callus forms
a. phagocytic cells clear debris
b. osteoblasts begin forming spongy bone after one week
c. fibroblasts secrete collagen fibers to connect bone ends
d. mass of repair tissue now called fibrocartilaginous callus


stage 3

bony calls forms
a. new trabeculae form a bony, hard callus
b. bony callus formation continues until firm union is formed in about 2 months


stage 4

bone remodeling
a. in response to mechanical stressors over several months
b. final structure resembles original