Thyroid Gland – Anatomy, Function, and Regulation of Metabolism

The thyroid gland (glandula thyroidea), located below the larynx, consists of two lateral lobes (“lobus dexter” and “lobus sinister”) connected 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 thyroid gland is shaped like the capital letter “H.” The lower lobes of the thyroid gland are broad and short, while the “upper horns,” which diverge slightly, are elongated and narrow.

Two connective tissue capsules surround the thyroid gland. The inner capsule is firmly attached to the thyroid’s connective tissue. The outer capsule borders the laryngeal muscles, nerve pathways and blood vessels on the sides, and the trachea at the back.

The volume of a healthy thyroid gland is a maximum of 18 milliliters in women and 25 milliliters in men. The gland weighs between 18 and 60 grams; in newborns, it weighs 2 to 3 grams. The thyroid lobes are three to four centimeters high and one to two centimeters thick. The width of the thyroid gland is 7 to 11 centimeters.

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 calcitonin, a hormone important for bone formation.

Thyroid tissue consists of microscopic sacs (thyroid follicles), which are usually round or oval in shape. The thyroid hormones T3 and T4 are responsible for the production of the cells that form the thyroid follicles (“thyrocytes” or “follicular epithelial cells”). In the strict sense, thyroid hormones are the T3 and T4 hormones—which consist largely of iodine—produced in the follicular epithelial cells. T3 contains three iodine molecules, while T4 contains four.

The so-called C-cells, which are located between the follicular epithelial cells, produce the hormone calcitonin. Calcitonin promotes the incorporation of phosphate and calcium into the bones, thereby inhibiting bone resorption.

On the back of the thyroid gland are the four lentil-sized parathyroid glands (glandulae parathyroideae, epithelial bodies), which produce the hormone parathyroid hormone (parathyrin, PTH). Parathyroid hormone regulates the calcium level in the blood.

The thyroid gland produces an average of 50 micrograms of the hormone T3 and 80 micrograms of T4 per day. The hormones, which are initially stored in the thyroid gland, are released into the bloodstream as needed. Metabolic processes consume half of the available hormone supply within 19 hours (T3) or 8 days (T4).

Thyroid hormones, which interact closely with other hormones (the endocrine system), influence metabolic processes and the function of numerous organs in the body and are also particularly important for physical growth.

Thyroid hormones

• affect the heart and circulatory system by increasing heart rate and blood pressure when necessary and dilating blood vessels,
• increase the metabolic rate of fat, sugar, and connective tissue,
• increase the activity of sebaceous and sweat glands,
• increase intestinal activity, and
• lead to increased excitation of nerve cells.

The thyroid gland is regulated by the pituitary gland and the hypothalamus, an important part of the diencephalon. The hormone TSH, produced by the pituitary gland, travels through the bloodstream to the thyroid gland, where it promotes its growth and the release of the hormones T3 and T4. The T3 and T4 hormones produced, on the other hand, inhibit further TSH secretion. This “negative feedback” ensures a stable metabolism. The hypothalamus, in turn, controls, among other things, the production of hormones by the pituitary gland.

The type of thyroid examination depends on the reason for the examination and the medical specialty of the examining physician (general practice, internal medicine, endocrinology, radiology, or nuclear medicine).

First, the doctor conducts a medical history interview with the patient to document current symptoms and medical history (including medications and previous illnesses).

The subsequent physical examination includes palpation (feeling the neck) and also serves to identify other physical signs of thyroid disease. As an imaging procedure, the first step is an ultrasound examination, which reveals significant structural changes in the thyroid gland.

A scintigraphy, a nuclear medicine imaging procedure, complements the options for visualizing the thyroid gland. Specialized examinations can be performed using computed tomography (CT) and magnetic resonance imaging (MRI).

A blood test allows for the determination of values essential for the diagnosis:

• If the TSH level is normal, a major functional abnormality of the thyroid gland can usually be ruled out.
• Based on the levels of free T3 and T4 hormones in the blood, the doctor may diagnose hypothyroidism or hyperthyroidism.
• Certain conditions require testing for thyroid autoantibodies or tumor markers.

Thyroid dysfunction is the root cause of many diseases, such as tumor-like conditions, inflammation, benign and malignant tissue growths, and abnormal organ development. All thyroid disorders can disrupt hormonal metabolism.

Disorders of thyroid function often trigger symptoms in a wide variety of organs. These may include, for example,

• the nervous system and mental health,
• the cardiovascular system,
• muscles and skeleton,
• the skin, and
• sexual function.

Excessively high blood levels of thyroid hormones (hyperthyroidism) lead to an increased basal metabolic rate and, consequently, to increased energy expenditure. As a result, hyperthyroidism often leads to weight loss. Other symptoms of hyperthyroidism include nervousness and a rapid heartbeat.

Too little thyroid hormone (hypothyroidism) causes symptoms such as weight gain, fatigue, and difficulty concentrating. A deficiency of thyroid hormones during the embryonic stage or in childhood often results in severe mental and physical underdevelopment. An adequate supply of iodine is essential for the thyroid gland to produce sufficient hormones.

The Most Common Disorder: Enlargement of the Thyroid Gland

The most common thyroid disorder is an enlarged thyroid, which can affect the entire organ uniformly or only certain parts of it. When the thyroid is enlarged, those affected may sometimes feel a sensation of tightness or pressure.

In cases of pathological thyroid enlargement (goiter, struma), the thyroid gland expands downward due to lack of space. If this constricts the windpipe, breathing difficulties may occur. In 90 percent of all goiter cases, the cause of the condition is a long-term, diet-related iodine deficiency (iodine-deficient goiter).

Thyroid Cysts

Thyroid cysts consist of fluid-filled cavities. Cysts develop in association with

• iodine-deficient goiter,
• benign or malignant tumors (thyroid cancer),
• diseases affecting an entire organ system (“systemic diseases,” e.g., of the skin, nervous system, or muscles), as well as
• following injuries.

Cysts can be clearly visualized and evaluated diagnostically using ultrasound imaging (sonography). Fine-needle aspiration is also guided by ultrasound. A scintigraphy allows for the determination of the hormonal activity of cysts.

Treatment of cysts depends on the individual cause and the current symptoms. Possible treatment options include monitoring the cyst, medication, sclerotherapy, and surgical removal (for larger cysts that cause symptoms).

Hot and Cold Nodules

“Hot nodules” are hormone-producing areas of the thyroid gland that are no longer regulated by the pituitary hormone TSH. Hot nodules absorb increased amounts of iodine and release hormones uncontrollably (regardless of the body’s needs). Nodules that produce hormones autonomously (“thyroid autonomy”) are responsible for about half of all cases of hyperthyroidism. “Cold nodules” refer to areas of tissue growth in the thyroid that do not absorb iodine and do not produce thyroid hormones.

The risk of nodule formation is particularly high in patients with a history of goiter. While nearly all hot nodules are benign, up to five percent of all cold nodules may represent malignant tissue changes. Thyroid cancer usually originates in thyrocytes or C cells; less commonly, it arises from the thyroid’s connective tissue.

Thyroid Inflammation (Thyroiditis)

A bacterial or fungal infection often leads to acute thyroid inflammation (thyroiditis) within a short period of time. Thyroiditis is more likely to occur in individuals with a weakened immune system—for example, after chemotherapy or in cases of HIV infection. Two specific forms of thyroid inflammation are caused by a malfunctioning immune system. They are classified as autoimmune diseases, in which the body’s immune system mistakenly attacks the body’s own structures:

Hashimoto’s thyroiditis begins with hyperthyroidism but destroys thyroid tissue and therefore ultimately leads to permanent hypothyroidism. The destruction of thyroid tissue occurs because the body’s immune system mistakenly attacks the body’s own thyroid proteins. Hashimoto’s thyroiditis is a chronic condition that affects women significantly more often than men (ratio of 10:1) and, overall, about three percent of the population.

Graves’ disease is an autoimmune disorder of the thyroid in which the immune system produces antibodies against the thyroid’s thyrocytes. Graves’ disease always leads to an overactive thyroid. Other organs are also frequently affected by Graves’ disease. For example, 60 percent of those affected suffer from an increase in the volume of connective tissue behind the eyes (endocrine orbitopathy). Two percent of the population develops Graves’ disease, predominantly women (at a ratio of 5:1 compared to men).

Thyroid disorders are treated with medication, radioactive iodine, or surgery.

• For hypothyroidism, patients are often prescribed thyroxine (T4 hormone), which is available in tablet form.
• To treat hyperthyroidism, so-called thyreostatics are used, which inhibit the production of thyroid hormones.
• Surgery is performed to remove excess thyroid tissue (for example, in the case of a cold nodule or a goiter). The goal of thyroid surgery is to preserve as much thyroid tissue as possible to ensure hormone production remains as normal as possible. If this is not possible, the necessary hormone must be taken in tablet form (hormone replacement therapy).
• Radioiodine therapy is an alternative to surgery. The radioactive iodine taken orally accumulates in the thyroid gland and destroys glandular tissue through radiation.

The hormones produced by the thyroid gland are particularly important for the human body’s metabolism. An overactive or underactive thyroid often leads to diseases in other organs as well. Thyroid disorders are treated with medication, surgery, or radioiodine therapy. Since patients do not always notice symptoms of the condition, we recommend that you have your thyroid checked regularly by your primary care physician or a specialist.

The anatomy of the thyroid gland shows that it is located in the front of the neck, below the larynx, and has the characteristic shape of a butterfly. The gland consists of two lobes connected by an isthmus. The thyroid gland produces vital hormones; more specifically, it produces the thyroid hormones T3 and T4, which are crucial for numerous processes in the body. These hormones are produced in the cells of the thyroid gland and stored as small droplets before being released as needed.

The primary function of the thyroid gland is to regulate metabolism, as the effects of thyroid hormones influence nearly all organs. The concentration of thyroid hormones in the blood is crucial for maintaining the body’s balance. Disorders can take many forms: Hyperthyroidism occurs when the thyroid gland produces too many hormones, while hypothyroidism occurs when it produces too few. The causes of hypothyroidism can vary, and the condition is indicated when typical symptoms appear.

Structural changes also play a role, such as a pathologically enlarged thyroid gland or inflammation of the thyroid. Such thyroid disorders are among the most common hormonal disorders. The thyroid is a mobile organ whose size and total volume can vary from person to person. It is located in the front of the neck, just below the Adam’s apple, and can often be easily felt when swallowing.

Thyroid hormone production is monitored through thyroid function tests, which allow for the early detection of thyroid dysfunction. Overall, it is clear that the thyroid is a highly complex organ that plays a central role in the human body. In summary, it is clear that a healthy thyroid is essential, as changes related to the thyroid lead to a wide range of symptoms, and the thyroid influences numerous vital processes.

What is the function of the thyroid gland?

The thyroid gland produces hormones such as T3 and T4, which regulate metabolism and control important bodily functions.

Where is the thyroid gland located?

The thyroid gland is located in the front of the neck, below the larynx and in front of the trachea.

What are some common thyroid disorders?

The most common disorders include hyperthyroidism, hypothyroidism, goiter, and thyroid cancer.

What are the symptoms of a thyroid disorder?

Typical symptoms include nervousness, fatigue, weight changes, or an enlarged thyroid gland.

How is the thyroid examined?

The examination usually involves blood tests (TSH, T3, T4), an ultrasound, and, if necessary, additional imaging procedures.