Page 74 - The Cell in 40 Topics

The Cell in 40 Topics

which thyroxin is secreted is a special system created by God with His infi-
nite knowledge, consisting of two separate measurement and feedback
mechanisms. Both mechanisms are the result of matchless engineering de-
sign.
When the level of thyroxin in the bloodstream rises above normal,
thyroxin produces a very significant effect on the pituitary gland: It re-
duces the pituitary gland's sensitivity to TSH, the thyroid secretion hor-
mone (Figure 59).
If you think about it, a most marvelous structure is plain to see. The
hormone TSH's task is to set the pituitary gland in action and send a mes-
sage to the thyroid gland—which represents the second link in the chain of
command established for the production of the hormone thyroxin.
The system has been planned in such great detail that the increased
thyroxin takes a most intelligent measure to prevent any excess production
of itself, and so interrupts the chain of command responsible for that pro-
duction. Thus it is automatically able to slow down the production of thy-
roxin when the level of thyroxin in the bloodstream rises above normal
(Figure 60).
There's a second system that also determines the level of production
of thyroxin. Increased thyroxin affects the hypothalamus cells, which then
reduce the production of TSH—and thyroxin production is slowed accord-
ingly.
Figure 59.
When the level of
thyroxin in the
blood rises
above normal,
this hormone
erects a literal
barrier in front of
the pituitary
gland.

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