Thyroid diseases

The thyroid is a butterfly-shaped gland located at the base of the neck, just below the Adam's apple. It produces the thyroid hormone that is responsible for secreting the right amount of energy that the body needs at all times. The main thyroid diseases are hyperthyroidism, hypothyroidism, thyroid nodule, goiter, Graves' disease, and thyroiditis. They mainly affect women.

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Thyroid diseases in first person

Professionals and patients explain how you live with the disease
The function of the thyroid gland is to control the metabolism of the whole organism and regulate the function of cells of the body and different organs.

To understand what thyroid diseases are, it is first useful to explain what the thyroid is and what it does.  

The thyroid or thyroid gland is a butterfly-shaped endocrine gland located in the lower part of the front of the neck, above the sternum, in front of the trachea and the oesophagus. Under normal conditions it weighs between 15-20 grams but it can reach hundreds of grams if there is a goitre. It is formed by two lobes, right and left, joined by a central part called the isthmus. 

The right lobe is usually larger and more vascularised. The gland is made up of microscopic spherical units, called follicles, consisting of a line of follicular cells that are responsible for producing thyroid hormones. The thyroid also contains the parafollicular cells or C-cells that are responsible for producing calcitonin. 

What does the thyroid do?

Thyroid hormones help the body to use energy and keep the so-called "basal metabolism" stable. This maintains the body temperature required for the brain, heart, muscles and other organs to function under the optimal conditions necessary for the body's processes. 

The thyroid gland produces thyroid hormones that are secreted into the blood and reach all the tissues in the body. The main thyroid hormones are thyroxine (L-thyroxine or T4) and triiodothyronine (T3). The main thyroid hormone in the blood is T4, while T3 is formed only in some tissues (brain, liver) by converting T4.  

Producing a normal amount of thyroid hormones requires an adequate intake of iodine, at least 100-150 micrograms. This comes primarily from the diet.  

The thyroid works together with two other hormone-producing glands, the pituitary and the hypothalamus. The aim of this is to produce the exact amount of energy that the body needs at any given moment (low levels during sleep, high levels when you are awake, and even higher levels during physical activity).

The thyroid gland function is controlled primarily by the pituitary, a gland located at the base of the skull behind the bridge of the nose. If there is a lack of hormones, the pituitary acts through a positive stimulation-type control mechanism, and if there is an excess of hormones, through a negative feedback mechanism (inhibition).  

At the same level as the hypothalamus, above the pituitary gland, thyrotropin-releasing hormone (TRH) is synthesised. This acts at the level of the pituitary gland and induces the production of thyroid stimulating hormone (TSH). TSH stimulates the follicular cells to produce thyroid hormones.

If there is an excess of circulating thyroid hormones, these act on the hypothalamus and pituitary to decrease the production of TRH and TSH, respectively, to balance the hypothalamic-pituitary-adrenal axis and normalise thyroid hormone production. If, on the other hand, there is a lack of circulating thyroid hormones, TRH and TSH are stimulated and increased, so that thyroid hormone synthesis is induced. 

Thyroid Disease

The main thyroid diseases are: 

Thyroid gland with a downward pointing arrow indicating hypothyroidism

Hypothyroidism. It is a disease caused by a decrease in the normal function (hypofunction) of the thyroid gland. This means that the thyroid gland is not able to produce enough thyroid hormone to maintain normal body function. The most common forms are Hashimoto's thyroiditis and atrophic thyroiditis.

Thyroid gland with an upward pointing arrow indicating hyperthyroidism

Hyperthyroidism. It is the condition that occurs when the thyroid gland is overactive, meaning that it makes too much thyroid hormone.  

Mujer con ojos saltones y bulto en el cuello. Enfermedad de Graves

Graves-Basedow disease. This is the most common form of autoimmune hyperthyroidism, in which the thyroid is activated by antibodies that stimulate the thyroid hormone-producing cells. In addition to hyperthyroidism and diffuse enlargement of the thyroid gland, this disease typically affects the eyes and, in some cases, also the skin.

Glándula tiroides inflamada. Tiroiditis.

Thyroiditis. It is an inflammation of the thyroid gland caused by an autoimmune attack or a viral infection. In its first phase, this inflammation leads to the release of thyroid hormone from within the gland, causing hyperthyroidism and, subsequently, to a decrease in thyroid function, leading to hypothyroidism. This can be permanent (chronic thyroiditis) or temporary (subacute thyroiditis, postpartum thyroiditis). It can also be classified according to whether it is associated with pain or not, presence of goitre, or altered thyroid function.  

Tiroides con nódulo. Nódulo tiroideo.

Thyroid nodule. It is a group of thyroid cells that are grouped together in a cluster, a lump, forming a tumour. When a person has more than one thyroid nodule it is called a goitre. More than 95% of thyroid nodules are benign. Nodules may cause no symptoms or they may grow and cause discomfort because of their size, or because they function independently from the rest of the thyroid (toxic nodule). 

Mujer con un bulto en el cuello. Bocio

Goitre. The term "goitre" refers to abnormal enlargement of the thyroid gland, meaning that something is causing the thyroid to grow larger than normal. It is important to understand that the presence of a goitre does not necessarily mean that the thyroid is not functioning properly. A thyroid goitre can make normal amounts of thyroid hormones (euthyroidism), too many (hyperthyroidism), or too few (hypothyroidism).  

Glándula tiroides con una célula maligna. Cáncer de tiroides

Thyroid cancer. It is a disease that results from the abnormal and excessive growth of the cells of the thyroid gland. 

Substantiated information by:

Felicia Alexandra Hanzu
Mireia Mora Porta

Published: 31 May 2021
Updated: 31 May 2021

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