Page 73 - The Miracle of Hormones

The Rhythm Of Life:
The Thyroid Gland

How is the amount of this
Thyrotropin-releas-
hormone that needs to be secreted ing hormone (TRH)
determined? How is it that, except
Hypothalamus
in cases of illness, neither more
Pituitary gland
nor less of this hormone than is
Thyroid-stimulating
needed is secreted? hormone (TSH)
The amount of thyroxine
Thyroid hormone
secreted is determined by a spe-
cial system created by the great
Reduced TRH secretion
artistry of God. This system is
based on two separate, negative
Reduced TSH secretion
feedback mechanisms and is an
example of an incomparable won- Negative feedback
der of engineering design.
Too much thyroid
When the amount of thyrox- hormone
ine in the blood rises above nor-
Increased TRH secretion
mal, the thyroxine hormone
produces a very interesting effect
Increased TSH
on the pituitary gland and some- secretion
times directly on the hypothala- W eakened
feedback
mus: it reduces the sensitivity of
the pituitary gland to the TRH Less thyroid hor-
mone
hormone.
The function of the TRH hor-
When there is need for thyroxine, the
mone is to activate the pituitary hypothalamus sends a command to the
gland to send a command (the pituitary gland (TRH). The pituitary
gland that receives the command
TSH hormone) to the thyroid
understands that the thyroid gland
gland. This command is the sec- must be activated. The pituitary gland
immediately sends a command to the
ond point on the chain of com-
thyroid gland (TSH). In compliance with
mand in the production of the the order it receives, the thyroid gland
immediately produces thyroxine, and
thyroxine hormone.
the thyroxine is distributed throughout
The system is so intricately the body by the blood stream.
designed that the excess thyroxine

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