GASTROINTESTINAL TRACT
Let KD
b
wees ey
Expansion of Eq.
(8), letting S = 0, Aye whys and hae gives
1
exp(-A, t)
The GIT is treated as an open tube, and the lower large intestine (LLI) is the
eritical organ.
exp(-A,t)
aA (5 ni Tat
hOgAR hats)
Ong
exp(-A,t)
The contents of the LLI (My) are assumed to weigh 150 g and to remain in the
LLI an average of 18 hours or 0.75 day.
exp(-A_t)
(9)
+ Ky C-£ DG hr
: “XO
ie ~ APO VAD
her “h
Rearranging Eq.
Kf e
from subcompartments of the respiratory tract.
A
An
. Kk, Q-£)) | l-exp(-A t)
AWOY
> R,
L
ments b, d, and f reach equilibrium in < 10 days.
(10)
An
KF
L
AnTAL
Ay
(: ; —e) L
hy
(
a
AY
An
dQ,
“Fp 7 (0-75 {Q, + Q, (£24 + £0, + FD.) ]
AD
Ah
Transfer from subcom-
partment g (T, = 500 days) is significantly delayed.
- were)
AY
. kK G-£,) E ( - rt) L ( ; ans]
Ane
Thereafter, the rate of
transfer from these subcompartments to GIT is constant.
; maaared
rs
As the biological half-times
for pathways b, d, and f are < 1 day, the amounts of radionuclide in subcompart-
[eee - ee|
{
to its contents.
The radionuclide enters the GIT (Fig. 1) by ingestion (Q,) and by clearance
(9) gives
Qa Lo =y;7
ay-a
The dose to LLI is one half the dose
175 theb f£D
+ 0.7
8 521 -2 ae!
(11)
Let G,
G,
= Q + Q, (EP, + EP, + £,D5)s constant input
2
= re D.Q_, variable input
ggosol
G
G
1
2
= = 0.75 (2 + x5)
Qe
8
S(S+A,)
Q, = 0.75)
l-exp(-i a
G+ ¢, (—
&
(2)
T = 70 years = 25,550 days.
699
69E
(3)