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e
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MID FEMUR
eee
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Bes cecccsnccnanssnnecacen Msorcnne ewe R PRU ORE RUE SE EEE PES esmnegperseree”
MID TIBIA
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i
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460
Days
Fic. 42.—Thespecific activity of %Sr in different bones of the adult rabbit relative to the total skeleton after a single
venous injection.
ALL
VERTEBRAE
Ro@28/kg BONE
RATIO(
Ra226/kg WHOLE SKELETON
)
1.8 .
.
ALL
VERTEBRAE
0.6
04 L
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18
20
ft
22
24
26
28
30
32
34
36
38
40
YEARS CARRIED
Fie. 48.—Concentration of 228Re in different human bones relative to the total skeleton
RATIO
OF
THE
SPECIFIC
ACTIVITY
IN
THE
DIFFUSE
COMPONENT TO THAT OF THE WHOLE BODY
Loss of Radioisotopes as Seen Microscopically
Two theories are currently considered to explain the
loss of activity from bone, (1) resorption, i.e., the removal of bone by osteoclasts and (2) the loss of activ-
ity by exchange with the extracellular fluids. Bone
formation, and by inference boneresorption rates, have
been well documented by tetracycline labeling techniques. The rate of loss by exchange process is, how-
ever, much moredifficult to quantitate. In Figure
47 I have tried to document what is known abou
loss of activity by the exchange process. There ar:
main components of uptake of the alkaline eart!
seen in autoradiographs of bone, (1) a hotspot
ponent usually associated with areas of bone grt
and (2) a diffuse component which refers to lab
throughout the whole volume of the bone. These
components have been studied separately to eva
the loss of activity by exchange. The short-term uy}
on bone surfaces is ignored in these studies.