The thyroid gland
below the larynx, on each side of
and anterior to the trachea
thyroxine and triiodothyronine .
also secretes calcitonin.
is controlled primarily by thyroid
stimulating hormone (TSH)
is composed of large numbers of
closed follicles .
,Lined with cuboidal epithelial cells that secrete
into the interior of the follicles.
are filled with a secretory substance colloid.
Major constituent of colloid is the large
glycoprotein thyroglobulin contains the thyroid
hormones.
, Inactive Active
Size of the follicles varies
with the activity of the
gland.
when active
follicle is smaller,
amount of colloid is less,
cells are cuboidal or
columnar
when inactive active gland shows
amount of colloid is abundant scalloped edge of colloid
showing small
follicle large
reabsorption lacunae.
flat epithelial cells.
, Synthesis
Iodine is required for formation
(To prevent iodine deficiency, common table salt is iodized with
about 1 part sodium iodide to every 100,000 parts sodium chloride).
Iodides ingested orally are absorbed from the gastrointestinal tract
into the blood.
About one fifth are removed from the circulating blood by the cells
of the thyroid gland and used for synthesis of the thyroid hormones.
below the larynx, on each side of
and anterior to the trachea
thyroxine and triiodothyronine .
also secretes calcitonin.
is controlled primarily by thyroid
stimulating hormone (TSH)
is composed of large numbers of
closed follicles .
,Lined with cuboidal epithelial cells that secrete
into the interior of the follicles.
are filled with a secretory substance colloid.
Major constituent of colloid is the large
glycoprotein thyroglobulin contains the thyroid
hormones.
, Inactive Active
Size of the follicles varies
with the activity of the
gland.
when active
follicle is smaller,
amount of colloid is less,
cells are cuboidal or
columnar
when inactive active gland shows
amount of colloid is abundant scalloped edge of colloid
showing small
follicle large
reabsorption lacunae.
flat epithelial cells.
, Synthesis
Iodine is required for formation
(To prevent iodine deficiency, common table salt is iodized with
about 1 part sodium iodide to every 100,000 parts sodium chloride).
Iodides ingested orally are absorbed from the gastrointestinal tract
into the blood.
About one fifth are removed from the circulating blood by the cells
of the thyroid gland and used for synthesis of the thyroid hormones.
