The Thyroid

The thyroid is an endocrine gland, part of the body's endocrine system, and has a wide-ranging influence in control of the body's metabolism. It is also vital for normal development.

The endocrine system is one of the control systems of the body. Endocrine glands release chemicals called hormones into the bloodstream, which travel to their target organs and cells. They then bind to receptors either on cell surfaces or inside the cell, which results in a change in the activity of those cells.

These responses are relatively slow, taking from seconds to days to occur. In comparison, the nervous system, which uses electrical signalling directly to muscles and other tissues produces responses within fractions of a second. However, once initiated, endocrine effects tend to be more prolonged.

This Thyroid section of the website covers all aspects of the thyroid, including its anatomy, function and the history of thyroid surgery. The major diseases that affect the thyroid can be studied in more detail on their own webpages; just click on the areas of the menu to the left that interest you.

Diseases of the thyroid

There are a number of diseases that can affect the thyroid gland, although they generally fall into two groups: those that result in lumps or nodules in the thyroid (usually these are benign lumps, but they may also include cancers), and diseases that change the function of the thyroid without necessarily changing its size or shape.

Worldwide, iodine deficiency is the most common cause of thyroid disease. Iodine deficiency has long been known in Tasmania, but it is also present in parts of New South Wales and Victoria, particularly in Gippsland. In 2009, the use of iodised salt in bread became mandatory in Australia and New Zealand, and Australia is now considered iodine sufficient.

In Australia there are about 40,000 new cases of thyroid disease each year, including both problems with the structure of the gland, and problems with its function, or a combination of these problems. For example, the thyroid can become inflamed, and swollen, and produce too much (or too little) thyroid hormone, such as in thyroiditis.

Autoimmune thyroid disease is the most common cause of thyroid dysfunction in Australia, with some 12% of the population having positive antibodies, most commonly to thyroid peroxidase antibody (TPOAb), with a higher prevalence in women.

Goitre and Thyroid Nodules

An enlarged thyroid is known as a goitre. This enlargement can be diffuse and affect the whole thyroid gland, or only affect part or all of one lobe. Lumps or nodules in the thyroid can be single or multiple. When there are many lumps in the thyroid it is called a multinodular goitre, which is the most common form of thyroid disease. It is important to note that the vast majority of thyroid lumps are not cancerous.

Palpable thyroid nodules are found in about 5% of the population, and with ultrasound, this number rises markedly with age, up to 70% of the elderly population.

Change in thyroid activity

When a patient has normal thyroid function this is known as being euthyroid. This is the usual state, even when there is quite gross disease in the gland or even quite marked enlargement. Thyroid function can change however, producing syndromes each with their own set of symptoms, and both of these problems are detailed elsewhere on the website:

1) The thyroid secretion is increased (Hyperthyroidism or Thyrotoxicosis)

2) The thyroid secretion is subnormal (Hypothyroidism or Myxoedema)