Thyroid hormones: types and functions in the human body

The endocrine system is made up of all these glands and hormones that work in our body. Hormones play a very important role in the regulation of basic physiological processes; in addition, they are also mostly related to emotions.

In this article we will talk about thyroid hormones, A type of hormone synthesized by the thyroid gland and involved in metabolism. We will know its origin, its characteristics and its functions. In addition, we will analyze two important alterations that occur in the thyroid: hyperthyroidism and hypothyroidism.

    Thyroid hormones: characteristics

    Thyroid hormones are a type of hormone secreted in our body and whose functions are important. Specifically, there are two: thyroxine (T4) and triiodothyronine (T3). These hormones are produced by the thyroid gland, a very important gland that regulates the body’s metabolism.

    For its part, metabolism is involved in the processes that control the activity rate of different cells and tissues, and encompasses a series of biological and chemical changes that continuously occur in the cells of our cos.

    Thyroid hormones they are based on tyrosine (One of the 20 amino acids that make up proteins). Specifically, thyroid hormones are amino hormones, along with other hormones: adrenaline, norepinephrine, melatonin, and dopamine. Interestingly, these latter substances are in turn neurotransmitters (within the central nervous system [SNC]) And hormones (out of it).

    But how do amino hormones work? What they do is bind to receptors on the cell membrane, initiating a chain reaction in the cell. Let’s look at the characteristics of the two thyroid hormones:

    1. Thyroxine (T4)

    Thyroxine was discovered and isolated in 1910 by Edward Calvin Kendall, an American researcher. Specifically, he isolated this substance from the thyroid of pigs.

    In terms of functions, thyroxine it mainly stimulates the body’s metabolism, In addition to participating in other processes. Adequate and balanced thyroxine levels are important for proper functioning, as too high or too low levels can cause alterations throughout the body.

    This is what happens when thyroid disorders appear: hyperthyroidism (increase in thyroid hormones) and hypothyroidism (decrease in thyroid hormones), which we will explain in detail later.

    2. Triiodothyronine (T3)

    The second of the thyroid hormones, triiodothyronine, was discovered 42 years later than thyroxine, in 1952, by Jean Roche, a French biochemist.

    this hormone it also plays a central role in the control and regulation of the body’s metabolism. It stimulates the metabolism of carbohydrates and fats, thanks to the activation of oxygen consumption.

    In addition, triiodothyronine also is involved in different physiological processes in the body, such as growth, heart rate and body temperature (Like thyroxine). Finally, another function that it performs is to break down proteins in cells.

      Where do thyroid hormones come from?

      To understand where thyroid hormones come from, we will need to visualize an overall pattern of hormones and the endocrine system. The endocrine system is directed by the hypothalamus, The main secretory hormone and the structure that “controls”, connecting the nervous system to the endocrine system. This, in turn, gives rise to two types of hormones: releasing hormones, on the one hand, and oxytocin and vasopressin, on the other.

      While the former (releasing hormones) act on the anterior hypothalamus (or adenohypophysis), the latter (oxytocin and vasopressin) act on the posterior hypothalamus (or neurohypophysis). The neurohypophysis is the “storage organ” for these hormones.

      Further concretizing, the adenohypophysis produces trophic hormones, which in turn act on the glands; these produce the various hormones in the body. This is what happens with thyroid hormones: that are synthesized by the thyroid gland, which in turn receives signals from the adenohypophysis (Part of the hypothalamus, the anterior part).

      In other words, thyroid hormones (thyroxine and triiodothyronine) originate from trophic hormones, which in turn originate from the adenohypophysis. Specifically, thyroid hormones are stimulated by TSH and thyrotropin, a type of trophic hormone. Synthetically, these structures (TSH and thyrotropin) actually stimulate the release of thyroid hormones in the thyroid gland.

      thyroid gland

      The thyroid gland, or thyroid, is the structure that secretes thyroid hormones (in fact, it’s an organ). This butterfly-shaped endocrine gland is located in the neck region, Just above the collarbone and below the nut.

      It is not a very large structure and weighs around 30 grams. The thyroid plays a vital role in our body’s metabolism as well as other bodily functions such as body temperature. Outraged, its condition and functioning are closely linked to our state of health.

      Some of the functions in which the thyroid gland is involved, through the action of its thyroid hormones, are as follows:

      • Participation in growth.
      • Regulation of metabolism.
      • Body temperature regulation
      • Development of the nervous system.
      • Assimilation of nutrients.
      • Heart rate regulation.
      • Skin development.


      There are two major changes in the thyroid gland, Which affect your secretion of thyroid hormones: hyperthyroidism and hypothyroidism.

      1. Hyperthyroidism

      Hyperthyroidism is a high secretion of thyroid hormones; More precisely, secretes too much thyroxine. In other words, the thyroid is overactive, and as a result, the body’s metabolism is accelerated.

      This leads to significant weight loss, As well as rapid and / or irregular heartbeats. It is linked to symptoms of hyperactivation and mania (manic episodes of euphoria and over-excitement). Other common symptoms include irritability, mood swings, fatigue, muscle weakness, and trouble sleeping.

      Hyperthyroidism affects women more often than men. People over 60 are another particularly affected population.

      Its causes can be various; the most common cause is Gave’s disease, A type of autoimmune disease. Other possible causes are thyroiditis, excessive iodine intake, or thyroid nodules.

      2. Hypothyroidism

      Hypothyroidism would be the opposite alteration; involves poor secretion of thyroid hormones. Specifically, the thyroid it does not secrete enough thyroxine to be able to develop normal functions of the body.

      This involves alterations in the metabolism, which is deficient; thus, the person with hypothyroidism gains weight (easily put on weight) and also exhibits depressive symptoms, fatigue and swelling of the face, among others. Hypothyroidism, like hyperthyroidism, affects women more than men.

      The causes of hypothyroidism can be various; among them there is a genetic form called ‘hereditary goiter cretinism’, in which a deficiency of thyroid hormone leads to severe growth retardation, facial deformities, alterations in sexual development and a decrease in brain size and connections. synaptic. This deficiency in thyroid hormones also leads to intellectual disability.

      Bibliographical references:

      • Carlson, NR (2005). Behavioral physiology. Madrid: Pearson Education.
      • Netter, F. (1989). The nervous system. Anatomy and physiology. Barcelona: saved.

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