As one of the most important parts of the body the thyroid gland should be studied carefully 1. The largest of the endocrine glands, the thyroid, takes up and concentrates iodine.

Absorption by the body of iodine requires an adequate and appropriate dietary intake -- from seafood, eggs and milk, for example.

2. It is involved in hormone production that regulates metabolism in all tissues.

Tri-iodothyronine (T3) and thyroxine (T4) are the two circulating hormones that regulate metabolism.

The other hormone produced is calcitonin, which lowers serum calcium levels.

3. The normal functioning of the thyroid gland is essential to regulate basal metabolic rate; regulate the process of growth and tissue differentiation; and maintain normal mental and physical development.

4. The effect of the thyroid hormones on the rate at which tissues metabolize involves the speed of chemical reactions in tissues, amount of oxygen used and heat produced. Remembering the thyroid's functions helps us understand the functional consequences of thyroid problems.

5. It is easier to consider abnormalities under two broad categories: oversecretion (hyperthyroidism) and undersecretion (hypothyroidism). Abnormal secretion can be primary -- that is, due to abnormality not in the gland but elsewhere. For instance, there may be inadequate secretion of thyroid-stimulating hormone (TSH) by the pituitary.

6. To help identify the exact abnormality, an assessment of clinical manifestations associated with specific conditions and thyroid function, tests are carried out.

7. If these do not indicate a clear diagnosis, two common endocrine "dynamic tests" may be used. If undersecretion is indicated, "stimulation tests" are used. A primary abnormality is confirmed if there is no response. But if a normal response occurs, a secondary abnormality exists.

8. If oversecretion is indicated, suppression tests are used where a secretion suppressing substance is administered. A primary abnormality is excluded if there is a normal response or confirmed if there is failure to suppress secretion.

9. Hypothyroidism is classified as: * Primary, if the thyroid gland is unable to secrete sufficient amounts of hormone.

* Secondary, if the anterior pituitary does not secrete enough thyroid-stimulating hormone (TSH).

* And tertiary, if the hypothalamus does not secrete enough TRH.

10. Depending on the age of the individual when hypothyroidism is developed, it is classified as cretinism or myxoedema. Cretinism is a condition caused by lack of thyroid hormone ante/neonatally.

This could be due to a hereditary or congenital cause, aplasia of the thyroid gland or failure to have an adequate iodine intake during pregnancy.

Mental and physical development is severely impaired if treatment is not given in the early months of life.