Introduction

Tucked away at the base of the neck, in front of the windpipe (trachea), just below the Adam's apple, the thyroid gland measures only 2 inches across. It has two lobes connected in the middle, giving it the shape of a bow tie or butterfly. When the thyroid gland is functioning normally, as it does most of the time in most people, there is little reason to give a second thought to its shape or to any of its other characteristics.

The main purpose of the thyroid gland is to make the hormones thyroxine (T₄) and triiodothyronine (T₃). Thyroid hormones control the speed of many vital body functions (the body's metabolism). For example, thyroid hormones make the heart beat faster and cause the body to burn up calories more quickly. T₃ plays a much greater role than T₄ in controlling the speed of body functions.

Aging itself has only minor effects on the thyroid gland and thyroid hormones. As people get older, the thyroid gland shrinks and shifts lower in the neck. The level of T₃ may fall slightly, but the speed of vital body functions changes very little. However, thyroid disorders become more common with aging.

In some cases, thyroid disorders produce extremely subtle changes in thyroid function. More commonly, however, disorders cause a noticeable change in function, especially underactivity of the thyroid gland and decreased production of thyroid hormones (hypothyroidism). The entire thyroid gland may enlarge, or one or more thyroid nodules may develop. Any enlargement of the thyroid gland—with or without nodules—is called a goiter.

Disorders that affect thyroid function can be thought of as great masqueraders in older people, because these disorders so often cause symptoms that are easily mistaken for symptoms of other conditions or even as signs of getting old. Increased or decreased thyroid function can dramatically worsen the way an older person feels and can greatly diminish the ability to carry out daily activities. For these reasons, the great masqueraders must be unmasked and recognized for what they are so that they can be effectively treated.

For additional detail on this topic, see Regulation of Thyroid Hormones.

See the figure Locating the Thyroid Gland.