The thyroid is a gland situated on the front of the neck, just below the skin, and is made of two halves (lobes) of tissue, each one the size of half of a plum, connected in the front by a thin strap of tissue (the isthmus). The lobes are made up of brownish-red tissue, and are located on the sides of the larynx (voice box), just below the Adam?s Apple.
The thyroid is a very important organ because it secretes straight into the blood chemicals (hormones such as thyroxin or T4, T3, and others) which regulate the rate of body chemistry. The thyroid hormones promote physical and mental growth in children, and in both children and adults keep the person mentally alert and physically healthy and agile. In other words, the thyroid hormones keep the chemical body processes at the level of activity which is compatible with the challenges of normal life.
Body injury and disease may result from either underactivity of the thyroid gland known as hypothyroidism, or from hyperactivity of the gland known as hyperthyroidism.
This section addresses the disturbances associated with hypothyroidism, a condition in which the body is not supplied with the needed amounts of thyroid hormones.
The causes of hypothyroidism:
In most cases the reason for hypothyroidism is the inability of the thyroid to secrete sufficient amounts of thyroid hormones, but in rare cases it may be due to an inborn inability of body tissues to respond properly to the action of the hormones. The thyroid?s inability to secrete sufficient hormones may be due to a number of causes.
Absence of iodine in the diet may result in hypothyroidism because iodine is a central component of the hormones. In the past, inhabitants of Switzerland mountains who drank spring waters low in iodine developed mental and physical retardation in childhood. (Those were the individuals who were at that time medically diagnosed as idiots and cretins, according to their severity of mental retardation.) Today, most countries, including the United States, add iodine to commercial table salt to prevent hypothyroidism.
A much more common source of hypothyroidism is destruction of the thyroid gland by inflammation or scarring (thyroiditis), radiation, thyroid destructive drugs used in the treatment of overactive glands or cancer, and thyroid surgery.
A less common cause of hypothyroidism is damage to the so called higher controllers of the thyroid gland which receive feedback from the thyroid hormones present in the circulation. The thyroid is under the control of another hormonal gland, the pituitary or hypophysis (a pea-sized gland located at the base of the brain) which regulates the amount of hormone secreted by the thyroid gland through a hormone of its own (Thyroid Stimulating Hormone or TSH.) which, as its names indicates, stimulates the activity of the thyroid. If the amount of thyroid hormone circulating in the blood is too low for the body?s needs, the pituitary secretes TSH, stimulating the thyroid to increase its production of thyroid hormones.
Damage to the pituitary gland, or higher brain centers controlling the pituitary, can also cause hypothyroidism.
Manifestations of hypothyroidism:
In children hypothyroidism is manifested by both physical and mental retardation, with the children exhibiting stunted growth, a large tongue, coarse skin and an enlarged thyroid gland. (The thyroid is enlarged because, in spite of the defective secretion of hormone, it is under the influence of the pituitary gland which, sensing a low level of thyroid hormone, secretes increased amounts of TSH which expand the gland (goiter) in a futile attempt to increase the activity of the thyroid.)
Nowadays hypothyroidism is seen primarily in adults. It is more common in women, and large population studies have shown that as many as one woman in ten over the age of 65 has evidence of the earliest stages of hypothyroidism.
The symptoms may be insidious, starting with increased fatigue, low energy and sluggishness, marked constipation, low body temperature and an abnormal sensitivity to cold. Other signs include a coarse dry skin, coarse and brittle hair, puffiness of the face, loss of the outer ends of the eyebrows, a hoarse voice and often an enlargement of the thyroid. Other manifestations include: abnormal gain of weight, irregular or abnormal menstrual cycles (longer, heavier or more frequent), aches in joints, hands and feet, carpal tunnel syndrome and absence of sex drive. People with hypothyroidism often experience difficulties in concentration, volatile moods, restlessness and depression.
Risk factors for hypothyroidism include: a family history of thyroid disease, a history of thyroiditis, an autoimmune disease, thyroid surgery involving partial or total removal of the thyroid gland, radiation and treatment of hyperthyroidism.
The clinical suspicion of hypothyroidism must be confirmed by laboratory findings showing low blood levels of thyroid hormones. The tests often show high levels of TSH which is secreted by the pituitary (for the reasons previously mentioned), unless the thyroid deficiency is a result of damage to the pituitary gland itself.
Treating hypothyroidism is relatively easy because it consists of replacement of the missing thyroid hormone by a similar manufactured hormone (Synthroid – pure synthetic thyroxine) which is available in pill form.
Taking more Synthroid than prescribed by the physician is not a good idea because it may result in hyperthyroidism (overactivity of the thyroid), a condition which is associated with many health risks.
Desiccated (dried and powdered) animal thyroid, once the most common form of thyroid therapy, is rarely prescribed today because it also contains T3 (tri-iodothyronine), a rapidly acting thyroid hormone which produces more variable blood levels than pure thyroxine preparations. Gradually increasing doses of thyroxine are given until the blood levels of T4 and TSH are both in the normal range. In instances where the patient is elderly or has an underlying heart condition, it is extremely important to start with a very low dose of thyroid hormone until the body gets used to the more normal thyroid hormone levels.
Since the most common type of thyroid gland failure is an inherited condition called Hashimoto?s thyroiditis, examinations of the members of the family may reveal other individuals with thyroid problems.