Thyroid hormones are produced by the thyroid gland which is located in the lower part of the neck, below the Adam's apple. Thyroid hormones stimulate the metabolism of cells. The thyroid gland wraps around the trachea and has a shape that is similar to a butterfly formed by two wings (lobes) and attached by a middle part (isthmus).
The function of thyroid gland is to remove iodine from the blood and uses it to produce thyroid hormones. The two most important thyroid hormones are thyroxine (T4) and triiodothyronine (T3) representing 99.9% and 0.1% of thyroid hormones respectively. The hormone with the most biological activity (for example, the greatest effect on the body) is actually T3. Once released from the thyroid gland into the blood, a large amount of T4 is converted to T3 - the more active hormone that affects the metabolism of cells.
When thyroid glands produces abnormally low thyroid hormone, the condition is called hypothyroidism and this results in many disorders which may directly or indirectly involve the thyroid gland. Because thyroid hormone affects growth, development, and many cellular processes, inadequate thyroid hormone has widespread consequences for the body. Hypothyroidism is more common among elderly people, especially women, and affects 1.5 to 2 per cent of people over the age of 60 years. However, the condition also occurs in younger patients.
As term suggests, hyperthyroidism is a condition in which an overactive thyroid gland is producing an excessive amount of thyroid hormones that circulate in the blood. For most people with an increased metabolic rate, the thyroid gland will be enlarged which is known as a goitre. However, goitre does not always lead to an increase in metabolism.
Hypothyroidism which permanently decrease metabolism requires lifelong treatment with a medicine called thyroxine which is available in form of tablets. This medicine is generally started with a small dose which is then increased gradually until an accurate dose has been reached. When this has been achieved, it is usually necessary to check the patient's metabolic rate only once a year. Though this medicine has virtually no side effects, it is important that the patients watch out for symptoms of increased metabolism, which may occur if the dose is too high.
The medicines like carbimazole (Neo-mercazole) and propylthiouracil are used to reduce or prevent the production of the two metabolic hormones. If the person has very active symptoms then beta-blocker medicines, such as propranolol (eg Inderal LA) can be given to control the symptoms while the effect of the anti-thyroid medicine is building up. Though, metabolism returns to normal within one or two months, but the duration of the treatment depends on the type of illness causing the increased metabolism.
In diffuse toxic goitre, the doctor will usually try to end the treatment after one or two years. Blood checks need to be done at regular intervals since about 50 per cent of patients have recurrences within two years. In toxic nodular goitre, the medication is lifelong, again with regular blood checks to monitor the treatment.