Question

An enlarged thyroid gland can lead to symptoms that reflect either overproduction or underproduction of thyroid hormones. How are both of these conditions possible from an enlarged thyroid?

Answer 1

Enlargement of thyroid gland can be due to :-

Hypothyroidism with enlargement of thyroid gland:-

Hashimoto’s thyroiditis - It is a more common cause of goiter.

It is an autoimmune condition in which there is destruction of the thyroid gland by one’s own immune system. As the gland becomes more damaged, it is less able to make adequate supplies of thyroid hormone.

The pituitary gland senses a low level of thyroid hormone and secretes more TSH(Thyroid Stimulating Hormone) to stimulate the thyroid. This stimulation causes the thyroid gland to grow, which may produce a goiter.

Hyperthyroidism with enlargement of thyroid gland:-

Graves’ disease:- It is also a common cause of goiter.

In Grave's disease, the immune system produces a protein, called as thyroid stimulating immunoglobulin (TSI). As with TSH, TSI stimulates the thyroid gland to enlarge producing a goiter. However, TSI also stimulates the thyroid to make too much thyroid hormone (causes hyperthyroidism).

Since the pituitary senses too much thyroid hormone, it stops secreting TSH. In spite of this the thyroid gland continues to grow and make thyroid hormone. Therefore, Graves’ disease produces a goiter and hyperthyroidism.