What is the normal level of T3

Thyroid anatomy & function


The small butterfly-shaped organ is an important hormonal pacemaker in the human body. Thyroid diseases can therefore have far-reaching consequences for health.

Where are the thyroid and parathyroid glands located?

The thyroid gland (Latin name: Glandula thyreoidea) is located on the Front of the neck below the thyroid cartilage of the larynx, which explains its name. It consists of two main lobes that are connected by a narrow tissue bridge (isthmus) in front of the windpipe. This structure shows the typical image of a butterfly for the thyroid gland.

A healthy organ is about the size of a thumb and weighs on average between 18 grams (women) and 25 grams (men) in an adult. The thyroid gland is in close proximity to structures attached to the Voice and language training involved. The delicate vocal cord nerve (nervus laryngeus recurrens), which runs behind the thyroid gland to the larynx muscles, is particularly important.

Behind each thyroid lobe there is usually one at the upper and lower pole Parathyroidwhich owes its name to its anatomical position in the body. These are glands about the size of a grain of rice that produce the hormone parathyroid hormone. This hormone controls the blood concentration of calcium and other trace elements in the body through various mechanisms. Calcium in turn influences nerve and muscle function as well as bone metabolism. About 90 percent of people have four parathyroid glands. The others either have fewer or more parathyroid glands. Some people even have more than ten parathyroid glands.

What are the tasks of the thyroid gland?

In the thyroid, iodine and other substances are made into the Thyroid hormones educated. These messenger substances are part of a hormonal control loop and as such control almost all important body functions. They affect the heart and circulation, widen the blood vessels, accelerate the heartbeat and regulate blood pressure. But they also activate the fat and connective tissue metabolism, the sweat and sebum glands of the skin and the kidney and intestinal activity. In addition, the thyroid hormones are essentially responsible for many growth processes and increase the basal metabolic rate and energy consumption of the entire organism.

Thyroid hormones mainly affect ...

  • Heart activity and blood pressure
  • Energy metabolism, body weight
  • Carbohydrate metabolism, insulin production
  • Fat and protein metabolism, cholesterol levels
  • Brain activity, psyche
  • Muscle metabolism, muscle strength
  • Bowel movement, digestion
  • Growth and maturation of unborn babies in the womb and children

What thyroid hormones are there?

The two most famous hormones made in the thyroid are called Triiodothyronine (T3) and Thyroxine (T4). Both have an iodine content. Thyroxine has four iodine atoms (T4), triiodothyronine only three (T3). By splitting off an iodine atom, the less effective but more durable T4 can be converted into the shorter-lived, but more effective hormone T3.

Most of T3 and T4 are bound to special proteins in the blood (thyroxine binding protein). These serve as a means of transport to the relevant organs. Only a small proportion is present as free, i.e. unbound, hormone. One then speaks of free T3 and free T4. The free hormones are the only ones that act on the metabolism. In addition, the thyroid gland also contains the hormone in the so-called C cells Calcitonin educated. This messenger substance influences e.g. the calcium and bone metabolism.

How is hormone production specifically controlled?

A healthy thyroid produces around 80 to 100 micrograms of T4 and 10 to 50 micrograms of T3 per day. When and in what quantity the thyroid makes the stored hormones available to the body is controlled by the brain: namely by the hypothalamus (part of the diencephalon) and the pituitary gland (pituitary gland).

The pituitary gland is, so to speak, the first superordinate center. She is the conductor of the hormonal control circuit in which the thyroid is integrated. Because it forms the hormone TSH (Thyroid Stimulating Hormone), which stimulates the thyroid gland in its hormone production. If there are not enough thyroid hormones in the blood, TSH production is increased and the thyroid is stimulated to do more work. If, on the other hand, the thyroid is too active, the pituitary gland will decrease TSH and thus reduce thyroid function.

The controlled release of TSH in turn takes place with the help of TRH (Thyreotropin Releasing Hormone), a hormone that is released by the higher-level hypothalamus. This complex feedback mechanism enables the healthy thyroid to keep the concentration of hormones in the blood at a constant level.

Put simply, the thyroid acts like our body's gas pedal: If there are too many hormones (hyperthyroidism), the body and soul run over-revving, if too few hormones (hypothyroidism) go under-revving. The thyroid gland is part of a complex loop through which the Hormone release in balance should be held. If the hormonal balance is disturbed, the entire organism can quickly get out of whack.

Why is iodine so important?

No thyroid hormone without iodine. It is required as a raw material for the production of thyroid hormones, which are responsible, among other things, for regulating metabolic processes and stimulating body and organ growth.

The human body cannot produce iodine itself and can only store it to a very limited extent. Iodine is a essential trace element. This means that the iodine required by the body must be regularly taken in with food. It passes passively into the blood via the gastrointestinal tract and from there actively into the thyroid. The thyroid uses up to 80 percent of the iodine consumed daily.

Where is our daily iodine requirement?

In order to be able to produce enough thyroid hormones, the daily iodine requirement for adults is around 150 to 200 micrograms. The German Nutrition Society has formulated certain recommendations for iodine intake depending on the age and gender of a person.

The daily iodine requirement is for:

Iodine is indispensable and vital for humans - in every phase of life - beginning with the development of the child in the womb. Sufficient coverage of iodine requirements is therefore important, especially during an existing or planned pregnancy, because now two thyroid glands have to be supplied with iodine. While the mother is at increased risk of developing a goiter, the baby's brain and nervous system development depend on a good supply of iodine. The need is also increased during breastfeeding because the iodine is released with breast milk.

What are the risks of an iodine deficiency?

Germany is one of the most iodine regions in Europe. Thousands of years ago, glacier melt washed away the trace element. To date, iodine is only found in very small quantities in our soils, arable and pasture areas and in drinking water and is therefore largely absent from animal and human food. For many years, the area of ​​what is now the Federal Republic of Germany was declared an iodine deficiency country and the goiter was the most visible sign of this deficit.

It is true that the population's iodine supply has improved significantly in recent decades. The iodine intake has almost doubled compared to 1975, especially newborns and children now have a balanced iodine balance. However, experts assume that at least a third, if not half of the German population is still not optimally supplied with iodine. The daily deficit is estimated to be a third of the amount of iodine recommended by the German Nutrition Society (DGE).

As a result, pathological changes or disorders of the thyroid gland can occur. Every third German is affected, from the age of 45 even every second, women about as often as men. The most common is the iodine deficiency goiter, an extreme enlargement of the thyroid gland with and without lumps.

Patient with massive iodine deficiency goiter

However, the symptoms of iodine deficiency usually appear insidious, so that you hardly notice any symptoms at first. The body only sends clear warning signals when it is severely underactive.

Typical signs are:

  • Lack of drive
  • extreme tiredness
  • Growth and development disorders in children
  • Difficulty concentrating
  • Sensitivity to cold
  • Sense of tightness and pressure in the throat
  • Difficulty breathing and swallowing
  • Skin changes (damp or dry skin)

How can iodine deficiency be compensated for?

The easiest way to counteract an acute iodine deficiency is through food: the most important sources of iodine are sea fish and marine animals. They should be on the menu at least twice a week. Pollack, cod and plaice are particularly rich in iodine.

Consistent use of iodized table salt can also help to compensate for deficits and prevent goitering. Significant amounts of iodine can also be found in milk and eggs, but the feeding of the animals is crucial here.

An overview of the iodine content of various foods:

While in some countries the problem was solved by adding iodine in the drinking water or the iodized salt was simply made the standard salt, such as in Switzerland since the 1920s, nothing happened in this country for a long time. Help finally came from the food industry, which increasingly used iodized table salt. The same applies to canteens, restaurants, bakeries and butchers. The iodine supply of the population has improved significantly due to a growing range of foods and dishes made with iodized salt. However, additional iodine intake can also be harmful for patients with certain thyroid diseases such as hyperthyroidism or Hashimoto-type thyroiditis.