The
thyroid
is a
butterfly-shaped
endocrine
(hormone
secreting)
gland in
the neck
that is
found on
both
sides of
the
trachea
(windpipe).
It
secretes
the
hormone
Thyroxine
which
controls
the rate
of
metabolism.
The
thyroid
weighs
about
20-25
gms in
an
adult.
It is
butterfly
shaped
and it
consists
of two
lobes
which
are
connected
together
by a
median
isthmus
as shown
in the
picture.
It is
located
in the
front of
the neck
and is
situated
just
below
the
larynx
or the
Adams
apple.
The
function
of the
thyroid
gland is
to take
up
iodine
from the
foods
that we
eat and
to
convert
it into
thyroid
hormones
namely
Thyroxine
(T4) and
Triiodothyronine
(T3) and
Calcitonin
(which
is
involved
in
calcium
metabolism).
The
cells of
this
gland
combine
iodine
and the
amino
acid
tyrosine
to make
T3 and
T4.
Later T3
and T4
are then
released
into the
blood
stream
and are
transported
throughout
the body
where
they
control
the
general
metabolism
(conversion
of
oxygen
and
calories
to
energy).
The
regulation
of the
metabolism
of every
cell in
the body
requires
thyroid
hormones.
The
ratio of
production
of T4
and T3
is
80:20.
However,
T3 is
about 4
times
more
potent
than T4.
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The
production
of
thyroid
hormones
is under
direct
control
of the
pituitary
gland.
Pituitary
is an
endocrine
gland
which is
situated
at the
base of
the
brain
and it
secretes
certain
vital
hormones
which
includes
TSH
(Thyroid
stimulating
hormone)
or
Thyrotropin,
besides
others.
When the
level of
thyroid
hormones
(T3 and
T4)
falls
below
the
required
amount,
the
pituitary
gland
secretes
TSH
which
stimulates
increased
production
of T3
and T4.
As the
levels
of T3
and T4
keep
rising
in the
blood,
the
pituitary
senses
this and
reduces
TSH
production. |
The
hypothalamus
is that
part of
the
brain
which
produces
TRH (Thyrotropin
Releasing
Hormone).
TRH
regulates
the
production
of TSH
by the
pituitary,
i.e. it
has a
regulatory
control
over the
pituitary
gland. |
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