The thyroid gland, a small gland that regulates a large number of processes

Dr. Ana María Orlandi (*)

The thyroid is a small gland that weighs between 15 and 20 grams and is located in the anterior region of the neck. It is formed by two lobes connected by a band of thyroid tissue, called isthmus.

Its function is to capture the dietary iodine, so that it is used by thyroid epithelial cells, for cell synthesis and secretion. thyroid hormones (triiodothyronine T3 and thyroxine T4). The thyroid tissue contains, in smaller numbers, so-called parafollicular cells or C cells responsible for the synthesis of calcitonin.

Thyroid function is regulated by several factors. The most important is the hypothalamo-thyrofi-thyroid axis, which acts as a functional unit. This is a characteristic model of self-regulation, in which each component tries to maintain normal levels of T4 and T3.

Thyroid hormones regulate a large number of metabolic processes. Good development and growth depend on its normal functioning, as well as reproduction and adaptation to the environment. They also stimulate thermogenesis (heat production), the synthesis of structural proteins, enzymes and protein hormones and have effects on the metabolism of carbohydrates and fats.

The thyroid gland may be affected by pathologies affecting its function, morphology or combination thereof.

Regarding the assignment of its function, it should be mentioned the accompanying tables that have a diminished function (hypothyroidism) or increased (hyperthyroidism).

It is called hypothyroidism in the image which is characterized by a decrease in the secretion of thyroid hormones, produced in the vast majority of cases by a functional or organic alteration of the thyroid gland. This is what is called primary hypothyroidism. It is a pathology that can range from mild clinical and biochemical manifestations (subclinical hypothyroidism), to a more significant form of biochemical alteration and to the appearance of characteristic symptoms and signs (clinical hypothyroidism). ), arriving late for consultation or diagnosis. in extreme cases of myxedema coma, which can endanger the patient's life. The prevalence of hypothyroidism is variable, according to different population studies (2-4.1%). It is more common in women and its appearance increases with age. Chronic autoimmune thyroiditis or Hashimoto is the most common cause of hypothyroidism at any age, but its frequency increases with age, which explains the high prevalence of hypothyroidism in women with over 60, which reaches 10% if subclinical hypothyroidism is included.

Hyperthyroidism is the condition that occurs as a result of the significant increase in hormone levels, usually produced by the increased production and release of thyroid hormones in the circulation. There are several pathologies that can cause this condition. The most common are hyperthyroidism due to Graves' disease and that caused by Plummer's disease or toxic nodular goitre. The first is a disease of autoimmune etiology, with rapid onset of symptoms and characteristic signs of an excess of thyroid hormones associated with goiter (enlarged thyroid gland) and changes characteristic eyepieces. The second is an entity that occurs insidiously and with a milder or milder clinical manifestation, which leads to a frequent diagnosis in older subjects.

With regard to diseases that may affect the morphology or architecture of the thyroid, we must refer to nodular goiter. Nodular thyroid disease is common and clinically important. In areas where iodine intake is sufficient, patches are detected by palpation in 4-7% of the general population, while highly sensitive diagnostic methods such as high-resolution ultrasound, reach 20-65%. %. Thyroid nodules can occur at any age, although their prevalence increases with age, are infrequent at pediatric age and are 3 times more common in women than in men.

(*) Argentine Society of Endocrinology and Metabolism (SAEM).