Along with the hypothalamus and pituitary gland, the thyroid gland is an important component of the thyrotropic regulatory circuit. Disturbances of this hormonal regulatory circuit can lead to serious impairment and even to a life-threatening metabolic derailment (thyrotoxic crisis).
What is the thyroid gland?
Infographic on the anatomy and location of the thyroid gland, as well as the symptoms of hyperthyroidism and hypothyroidism. Click image to enlarge. The thyroid gland (thyroid glandula) is an endocrine gland that has a lobed, butterfly-shaped structure and surrounds the trachea (windpipe) below the larynx (larynx) in a semicircular fashion from back to front. On average, the thyroid gland weighs between 20 to 60 grams and plays an essential role within human metabolism (metabolism). The thyroid gland consists mainly of microscopically visible thyroid follicles in which the protein thyroglobulin, a precursor of thyroid hormones, is stored and between which the so-called C cells (calcitonin-producing cells) are located. For proper functioning, especially for the synthesis of thyroid hormones, the thyroid gland requires sufficient iodine, an essential trace element that enters the endocrine gland as iodide from the blood (iodination), where it is oxidized to elemental iodine and stored (iodization).
Anatomy and structure
The thyroid gland is composed of the two lateral lobes lobus dexter and lobus sinister, which are connected approximately between the 2nd and 4th tracheal rings via the so-called isthmus, a kind of tissue bridge, in front of the trachea, forming a butterfly-like shape. Often, at this tissue bridge, another process can be observed, which is pyramidal towards the thyroid cartilage (largest laryngeal cartilage), a functionless rudiment from embryonic development (lobus pyramidalis). In addition, the thyroid gland is enclosed by an inner and outer connective tissue capsule, through which the connection with the surrounding structures such as the supplying vessels and nerves is ensured. In addition, the connective tissue anchors the two lobes of the thyroid gland to the trachea. The thyroid gland has a very high vascularization (large number of blood vessels) and blood flow rate.
Functions and tasks
The most important function of the thyroid gland is to store iodine for synthesis and secretion (secretion) of iodine-containing thyroid hormones and to produce the peptide hormone calcitonin. In the so-called follicular epithelial cells (thyrocytes) of the thyroid gland, the hormones thyroxine or tetraiodothyronine (T4) and triiodothyronine (T3) are synthesized, which increase energy metabolism by dilating the vessels, stimulate the cells of the nervous system, and cause an increase in heart rate, blood pressure, and body temperature. In addition, thyroid hormones increase sebaceous and sweat gland activity, collagen synthesis and intestinal motor function, and play an essential role in the organic development of newborns. Through their effect on the growth hormones IGF-1 (insulin-like growth factor) and somatropin, they control growth and cell development. They also promote myelination (segregation) and differentiation of neurons. The function of the thyroid gland is controlled by the superior pituitary gland and the hypothalamus (area of the diencephalon). In addition, the hormone calcitonin is produced in the parafollicular cells or C cells located between the follicular epithelial cells. Calcitonin has a reducing effect on the calcium concentration in the blood, as it inhibits the release of calcium and phosphate in the bones, while at the same time stimulating the incorporation of these substances (mineralization). In addition, the hormone stimulates the release of phosphate, sodium, calcium, potassium, and magnesium from the kidney.
Diseases
Diseases of the thyroid gland are comparatively common and can generally be divided into three different subtypes. If a normal thyroid hormone level is present, it is referred to as euthyroidism. In the case of a disturbed thyroid hormone metabolism, the hormone level is either increased as a result of hyperthyroidism (hyperthyroidism) or decreased as a result of hypothyroidism (hypothyroidism). In hyperthyroidism, the body’s energy metabolism increases, so in many cases hyperthyroidism is manifested by weight loss. Palpitations and/or nervousness are further symptoms of hyperthyroidism.Hypothyroidism is differentiated into primary hypothyroidism due to impairment of the thyroid gland itself and secondary hypothyroidism due to impairment of the structures controlling the thyroid gland (pituitary, hypothalamus). An underactive thyroid gland is usually manifested by bradycardia, listlessness, impaired concentration, sensitivity to cold, constipation and weight gain. Regardless of the specific metabolic condition, the thyroid gland may be enlarged as a result of struma formation (goiter) or it may be normal in size. Thus, physicians refer to an enlargement of the organ with a normal hormonal metabolic state as a euthyroid goiter, which is one of the most common diseases with an incidence of 30 to 40 percent of the population. A pronounced goiter can narrow the trachea and cause breathing difficulties. In addition, the risk for thyroid autonomy is greatly increased. Inflammation of the thyroid gland (thyroiditis) can in many cases be traced back to autoimmune diseases (Hashimoto’s thyroiditis, Graves’ disease) or noxae (drugs, chemotherapy). Malignant neoplasms (carcinomas) generally develop in the thyroid gland starting from thyrocytes or C cells.
Typical and common diseases
- Thyroid cancer
- Goiter (goiter, enlargement of the thyroid gland)
- Hyperthyroidism
- Hypothyroidism
