The Thyroid gland
The
Thyroid
gland
is one of the largest endocrine glands in the body. It is positioned on the
neck just below the Larynx and has two lobes with one on either side of the
trachea. It is involved in the production of the
hormones T3 (triiodothyronine) and T4 (thyroxine). These hormones increase the metabolic
activity of the body‘s cells. The thyroid also produces and
releases the hormone calcitonin (thyrocalcitonin)
which contributes to the regulation of blood calcium levels.
Thyrocalcitonin or calcitonin decreases
the concentration of calcium in the blood. Most of the calcium removed from the
blood is stored in the bones.
The
thyroid hormone consists of two components, thyroxine and iodine. This hormone
increases the metabolism of most body cells. A deficiency of iodine in the diet
leads to the enlargement of the thyroid gland, known as a simple goiter. Hypothyroidism
during early development leads to cretinism. In adults, it produces myxedema,
characterized by obesity and lethargy. Hyperthyroidism leads to a condition
known as exophthalmic goiter, characterized by weight loss as well as
hyperactive and irritable behavior.
The
thyroid gland is a two-lobed gland that manifests a remarkably powerful active
transport mechanism for up-taking iodide ions from the blood.
As
blood flows through the gland, iodide is converted to an active form of iodine.
This iodine combines with an amino acid called tyrosine. Two molecules of
iodinated tyrosine then combine to form thryroxine. Following
its formation, the thyroxine becomes bound to a polysaccharide-protein material
called thyroglobulin. The normal thyroid gland may store several weeks supply
of thyroxine in this bound form. An enzymatic splitting of the thyroxine from
the thyroglobulin occurs when a specific hormone is released into the blood.
This
hormone, produced by the pituitary gland, is known as thyroid-stimulating
hormone (TSH). TSH stimulates certain major rate-limiting steps in thyroxine
secretion, and thereby alters its rate of release. A variety of bodily defects,
either dietary, hereditary, or disease induced, may decrease the amount of
thyroxine released into the blood.
Thyroxine serves to stimulate
oxidative metabolism in cells; it increases the oxygen consumption and heat
production of most body tissues, a notable exception being the brain. Thyroxine is also necessary for normal
growth. The most likely explanation being
that thyroxine promotes the effects of growth hormone on protein synthesis. The absence of thyroxine significantly
reduces the ability of growth hormone to stimulate amino acid uptake and RNA
synthesis. Thyroxine also plays a crucial
role in the closely related area of organ development, particularly that of the
central nervous system.
If
there is an insufficient amount of thyroxine, a condition referred to as hypothyroidism
results. Symptoms of hypothyroidism stem
from the fact that there is a reduction in the rate of oxidative
energy-releasing reactions within the body cells. Usually the patient shows
puffy skin, sluggishness, and lowered vitality. Other symptoms of hypothyroidism
include weight gain, decreased libido, inability to tolerate cold, muscle pain
and spasm, insomnia and brittle nails.
Sumber : Bpk. Dr. Iskandar Zulkarnain
#posting tugas cyberprenership
ahmad baihaqi
NIM 1112503964
