The thyroid gland is the largest endocrine gland in the body. The hormones produced by the thyroid gland are of great importance for the body's metabolism and for the functioning of many body organs. We will inform you about the function of the thyroid gland as well as thyroid diseases and treatment options.
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Article overview
Structure and location of the thyroid gland
The thyroid gland (glandula thyroidea), which is located below the larynx, consists of two lateral lobes ("lobus dexter" and "lobus sinister"), which are connected to each other by a narrow strip of tissue ("isthmus"). The thyroid lobes rest laterally on the trachea, which they surround below the larynx and to which they are connected by connective tissue. The shape of the thyroid gland resembles the capital letter "H". The lower branches of the thyroid gland are broad and short, while the slightly divergent "upper horns" have an elongated and narrow shape.
Two connective tissue capsules surround the thyroid gland. The inner capsule is firmly attached to the thyroid connective tissue. The outer capsule borders on the laryngeal muscles, laterally on nerve tracts and vessels and at the back on the trachea.
The volume of a healthy thyroid gland is a maximum of 18 milliliters in women and 25 milliliters in men. The endocrine gland weighs between 18 and 60 grams, in newborns 2 to 3 grams. The thyroid lobes are three to four centimetres high and one to two centimetres thick. The width of the thyroid gland is 7 to 11 centimeters.
Function of the thyroid gland
The primary function of the thyroid gland is to store iodine and produce the iodine-containing hormones triiodothyronine (T3) and thyroxine (T4) as well as the hormone calcitonin, which is important for bone formation.
The thyroid tissue consists of microscopically small blisters(thyroid follicles), which are usually round or oval in shape. The thyroid hormones T3 and T4 ensure the production of the cells that form the thyroid follicles ("thyrocytes" or "follicular epithelial cells"). Thyroid hormones in the narrower sense are the T3 and T4 hormones consisting largely of iodine, which are produced in the follicular epithelial cells. T3 contains three iodine molecules, T4 four.
The so-called C-cells, which are located between the follicular epithelial cells, produce the hormone calcitonin. Calcitonin causes the incorporation of phosphate and calcium into the bones and thus inhibits bone resorption.
The four lentil-sized parathyroid glands (glandulae parathyroideae, epithelial corpuscles), which produce the hormone parathyroid hormone (parathyrin, PTH), are located at the back of the thyroid gland. Parathyroid hormone regulates the calcium level in the blood.
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The thyroid hormones T3 and T4
The thyroid gland produces an average of 50 micrograms of the hormone T3 and 80 micrograms of T4 per day. The hormone quantities initially stored in the thyroid gland are released into the blood as required. Due to metabolic processes, half of the available hormone quantity is used up in 19 hours (T3) or 8 days (T4).
The thyroid hormones, which interact closely with other hormones(hormone system), influence metabolic processes and the function of numerous body organs and are also particularly important for body growth.
Thyroid hormones
- influence the heart and circulation by increasing the heart rate and blood pressure and dilating blood vessels,
- increase the metabolism of fat, sugar and connective tissue,
- increase the performance of sebaceous and sweat glands,
- increase intestinal activity and
- lead to increased excitation of nerve cells.
The thyroid gland is controlled by the pituitary gland and the hypothalamus, an important part of the diencephalon. The hormone TSH produced by the pituitary gland reaches the thyroid gland via the bloodstream, where it promotes its growth and the release of the T3 and T4 hormones. The T3 and T4 hormones produced, on the other hand, inhibit the further release of TSH. This "negative feedback" ensures a stable metabolism. The hypothalamus in turn controls the production of hormones by the pituitary gland, among other things.
Examination of the thyroid gland
The type of thyroid examination depends on the reason for the examination and the specialist discipline of the examining doctor (general medicine, internal medicine, endocrinology, radiology or nuclear medicine).
First of all, the doctor conducts a medical history interview with the patient to record the acute symptoms and medical history (including medication and previous illnesses).
The subsequent physical examination includes palpation (palpation of the neck) and also serves to identify other physical signs of thyroid disease. The first imaging procedure is sonography (ultrasound examination), which reveals significant structural changes in the thyroid gland.
Scintigraphy, a nuclear medicine imaging procedure , completes the possibilities of thyroid imaging. Special examinations are possible using computer tomography and magnetic resonance imaging.
A blood test makes it possible to determine values that are essential for the diagnosis:
- If the TSH value is normal, a major functional abnormality of the thyroid gland can usually be ruled out.
- Based on the levels of free T3 or T4 hormones in the blood, the doctor may diagnose hypothyroidism or hyperthyroidism.
- Certain diseases make it necessary to test for thyroid autoantibodies or tumor markers.
Common diseases of the thyroid gland
A malfunction of the thyroid gland is the starting point for many diseases, such as tumor-like diseases, inflammations, benign and malignant tissue formations and impaired organ development. All thyroid diseases can impair hormone metabolism.
Disorders of thyroid function often trigger symptoms in various organs. The following, for example, may be affected
- Nervous system and psyche,
- cardiovascular system,
- muscles and the skeleton,
- skin and
- sexual function.
Too high a blood level of thyroid hormones(hyperthyroidism) leads to an increased basal metabolic rate of the body and therefore to increased energy consumption. As a result, hyperthyroidism often leads to weight loss. Other symptoms of hyperthyroidism include nervousness and palpitations.
An insufficient amount of thyroid hormones(hypothyroidism) triggers symptoms such as weight gain, tiredness and difficulty concentrating. A thyroid hormone deficiency in the embryonic stage or in childhood often causes severe mental and physical underdevelopment. A sufficient supply of iodine is a prerequisite for the thyroid gland to be able to produce enough hormones.
The most common disease: enlargement of the thyroid gland
The most common disease of the thyroid gland is enlargement, which can affect the entire organ or individual parts of it. When the thyroid gland is enlarged, those affected sometimes feel a feeling of tightness or pressure.
In the case of a pathological enlargement of the thyroid gland( goitre), the thyroid gland expands downwards due to a lack of space. If the windpipe is constricted as a result, breathing difficulties may occur. In 90 percent of all goitre cases, the cause of the disease is a diet-related, long-term iodine deficiency (iodine-deficient goitre).
Thyroid cysts
Thyroid cysts consist of fluid-filled cavities. Cysts develop in connection with
- an iodine deficiency goitre,
- benign or malignant tumors(thyroid cancer),
- diseases of an entire organ system ("systemic diseases", e.g. of the skin, nervous system or muscles) and
- after injuries.
Cysts can be easily visualized and assessed using ultrasound imaging (sonography). Fine needle puncture is also guided by ultrasound. Scintigraphy makes it possible to determine the hormonal activity of cysts.
Cysts are treated according to the individual cause and the current symptoms. Possible forms of treatment include observation of a cyst, medication, sclerotherapy and surgical removal (for larger cysts that cause symptoms).
Hot and cold lumps
"Hot nodules" are hormone-producing areas of the thyroid gland that are no longer controlled by the pituitary hormone TSH. Hot nodules absorb more iodine and release hormones in an uncontrolled manner (independent of the body's needs). Nodules that produce hormones autonomously ("thyroid autonomy") are responsible for around one in two cases of hyperthyroidism. "Cold nodules" are tissue proliferations in the thyroid gland that do not absorb iodine and do not produce thyroid hormones.
The risk of nodules forming in the presence of a goitre is particularly high. While almost all hot nodules are benign, up to five percent of all cold nodules can be malignant tissue changes. Thyroid cancer usually originates from thyrocytes or C-cells, less frequently from the connective tissue of the thyroid gland.
Inflammation of the thyroid gland (thyroiditis)
A bacterial or fungal infection often leads to acute thyroid inflammation (thyroiditis) within a short period of time. Thyroiditis is facilitated by a weakened immune system - for example after chemotherapy or in the case of an HIV infection.
Two specific forms of thyroid inflammation are caused by a misdirected immune system. They are autoimmune diseases in which the body's immune system mistakenly attacks the body's own structures:
Hashimoto's thyroiditis begins with hyperthyroidism, but destroys the thyroid tissue and therefore eventually leads to permanent hypothyroidism. The destruction of the thyroid tissue is due to the body's immune system mistakenly fighting the body's own thyroid proteins. Hashimoto's thyroiditis is a chronic disease that affects women significantly more often than men (ratio 10:1) and around three percent of the population.
Graves' disease is an autoimmune disease of the thyroid gland in which the immune system produces antibodies against the thyrocytes of the thyroid gland. Graves' disease always leads to hyperthyroidism. Other organs are also frequently affected by Graves' disease. For example, 60 percent of patients suffer from an increase in the volume of the connective tissue behind the eyes (endocrine orbitopathy). Basedow's disease affects two percent of the population, most of whom are women (in a ratio of 5:1 to men).
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Treatment of thyroid disorders
Thyroid disease is treated with medication, administration of radioactive iodine or surgery.
- Patients with hypothyroidism are often given thyroxine (T4 hormone), which is available in tablet form .
- So-called thyreostatics, which inhibit the production of thyroid hormones, are available for the treatment of hyperthyroidism.
- Surgery is used to remove excess thyroid tissue (e.g. in the case of a cold nodule or goitre). The aim of thyroid surgery is to preserve as much thyroid tissue as possible in order to ensure normal hormone production. If this is not possible, the necessary hormone must be taken in tablet form (hormone replacement therapy).
- Radioiodine therapy can be considered as an alternative to surgery. The ingested radioactive iodine accumulates in the thyroid gland and destroys glandular tissue through radiation.
The thyroid gland - great importance of a supposedly small organ
The hormones produced by the thyroid gland are particularly important for the human body's metabolism. An overactive or underactive thyroid gland often leads to diseases of other organs. Thyroid disease is treated with medication, surgery or radioiodine therapy. As sufferers do not always notice symptoms of the disease, we recommend that you have a regular thyroid check-up with your GP or specialist.
