In the thymus, immune cells experience their imprint - but only in the first years of life. Learn here why the thymus is no longer active in adults.


Of the thymus (Thymus, Bries) is an important part of the immune system. In the thymus certain white blood cells (lymphocytes) get their immunological imprinting, at the same time the maturation of disease-fighting T cells is stimulated by thymus hormones. The thymus gland is only active during childhood and adolescence. Read here everything about the thymus and its function as a "school of the body police".

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  • What is the thymus?

  • What is the function of the thymus?

  • Where is the thymus?

  • What problems can the thymus cause?

What is the thymus?

The thymus plays a significant role in the human immune system. In this small organ, some of the white blood cells (T lymphocytes or T cells) learn to recognize and attack foreign cells. For this, the immune cells are characterized in such a way that they can distinguish the body's own surface structures (antigens) from, for example, bacteria or viruses from foreign antigens. This is important to prevent the immune cells attacking their own body and causing so-called autoimmune diseases.

The thymus consists of a right and a left lobe, both of which are surrounded by a connective tissue capsule. Connective tissue strands pass through the lobes from this capsule and subdivide the thymus into many small lobules called lobuli thymi. Each lobule consists of a bright medulla surrounded by a darker cortex.

In the medullary zone of the thymus are the characteristic Hassall bodies. Above all, they are easy to see optically under the microscope. The Hassall bodies are likely to be composed of coalesced cover tissue cells (epithelial cells) and look like little onions through this layering. Their function is not yet clear, but it is believed that they help in the maturation of immune cells.

Change in the thymus gland

The thymus is not equally active throughout life: even before birth, the thymus gland begins its work with the production and maturation of T lymphocytes.

In the newborn, the thymus cicra is five inches long and two inches wide. From childhood to puberty, the thymus reaches its maximum weight of 35 to 50 grams. From sexual maturity the thymus gland shrinks. Function and tissue change. In old age you will find there mostly fat and connective tissue, the weight is reduced to about three grams. This process is called Thymusinvolution. However, most of the training of immune cells is already completed.

After its regression, the secondary lymphatic organs (lymph nodes, spleen) take over the tasks of the thymus.

What is the function of the thymus?

The thymus, together with the bone marrow, is called the primary lymphatic organ. This means that in the thymus and bone marrow, the immune system develops and matures.

To do this, the immune cells go through several stations:

bone marrow

From the bone marrow migrate "multipotent stem cells", it is precursor cells whose fundamental function is already known, but the development is not yet complete.


These cells enter the thymus via the bloodstream. To obtain the imprinting and differentiation, the progenitor cells (thymocytes) must pass through the thymus from the cortex to the medullary region and then be released back into the bloodstream as T lymphocytes.

Imprint of immune cells

The embossing takes place in three steps. Subsequently, those cells are sorted out that have not been "trained" properly or not well enough. Over 90 percent of imprinted cells are eliminated.

At the end of imprinting and selection, the remaining T lymphocytes have learned to differentiate endogenous tissue from the body by recognizing the surface structures accordingly. Later, they can identify and attack bacteria, viruses, parasites or tumor cells, sprouting the body's own cells.

Rearrangement in the lymph nodes

After their "training", the T lymphocytes are released back into the blood and enter the lymph nodes. There they wait for their assignment. If a T cell recognizes its own special surface molecule in an intruder, this T cell proliferates. Together, the clones attack bacteria. How to ward off an infection.

Thymus gland: hormone production

Why is this organ also called the thymus gland? The function of the thymus as a gland is also the production of thymosin, thymopoietin I and II. These hormones play a role in the maturation and differentiation of T lymphocytes in the thymus.

Every day we are exposed to countless pathogens. Learn how the defense works.

Where is the thymus?

The thymus is located in the thorax, directly in the middle behind the upper third of the breastbone (sternum).It is located above the pericardium in the middle part (mediastinum) and extends from the attachment of the clavicle to the fourth pair of ribs. Due to its location above the pericardium, the thymus sits on the large vessels of the heart, the main artery (aorta) and the superior vena cava (superior vena cava). Laterally, the thymus is bordered by the pleura and lungs.

What problems can the thymus cause?

The complex structure of the thymus can lead to more frequent anomalies. This does not necessarily mean that its function is impaired. If so, then impairment usually plays a role, especially at a young age, when the thymus is active.

For example, there are congenital disorders in which the thymus is not formed (thymic aplasia) or only partially. This developmental disorder can lead to pronounced immunodeficiencies with a high susceptibility to infection. Often thymic aplasia is also a concomitant of other hereditary defects, such as DiGeorge's syndrome, retinoid embryopathy, Louis-Bar syndrome or Wiskott-Aldrich syndrome.

Especially in early infancy, it can happen that the thymus enlarges (persistent thymic hyperplasia) and presses on the trachea, so it comes to breathing difficulties. Most of the time, however, this spontaneously returns.

The thymus also appears to play a role in a particular severe autoimmune disease of the skeletal muscle (myasthenia gravis pseudoparalytica) - in many patients the thymus is also enlarged

in the thymus can also form an abscess. An infection with pus formation encapsulates an abscess. It is also possible that benign (thymomas) or malignant tumors (thymic carcinomas) develop.

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    Surrounded by germs

    Man is constantly surrounded by viruses and bacteria. And they take every chance to penetrate the body. To prevent that, the immune system works day and night at full speed. Read here, which "immune sins" weaken the body defense and make the body more susceptible to colds, flu and co.

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    Defense forces need sleep

    Lack of sleep appears to affect the ability of the organism to produce antibodies. This was shown by an experiment: Volunteers who had been woken up one night after a vaccination had only developed half as many antibodies after ten days as subjects of a control group who slept sufficiently. Those who sleep less than six hours a day catch their cold faster than those who sleep more than eight hours.

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    Bacteria love fast food

    A balanced diet keeps all body systems going - including the immune system. Those who eat unhealthy food and are more likely to eat fast food and sweets than fruits and vegetables risk permanently a lack of vitamins and minerals. Especially in the cold season, they are especially important for keeping the immune system at bay and dangerous viruses and bacteria in check.

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    Ice feet pave the way for pathogens

    Cold feet are not only unpleasant - they also make you sick. If the body registers that the feet have cooled down, it initiates measures against further cooling. It narrows the blood vessels throughout the skin and mucosa. The result: The nasopharyngeal space is poorly supplied with blood and thwarted the immune system so. Viruses and bacteria can then easily nest in the mucous membranes and cause infections.

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    Good sport, harmful sport

    Sport is healthy - but beware: those who overdo it with physical activity, weakens the immune system. Instead of strenuous endurance sports enthusiasts should change in the winter, especially when many pathogens are on the move, to moderate and regular physical activity. For exercise activates the various immune cells, so that invading viruses and bacteria can be better controlled.

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    Stress opens the doors to viruses

    The immune system reacts enormously to stress, because it puts the body in an alarm state. Special stress hormones, for example, prepare the body systems for flight and fight. For a short time, this process can help to achieve peak performance. At the same time certain immune functions are suppressed. Chronic stress is therefore poison for the body. Because then viruses and bacteria can spread without much resistance.

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    Germs benefit from alcohol

    Viruses and bacteria are easier to play under the influence of alcohol. A study shows that alcohol hinders the work of special immune cells (monocytes): they lose their immune-stimulating and especially anti-virus properties. Influenza viruses, colds but also serious viral diseases such as hepatitis C can no longer be warded off so well. In addition, the body will cope worse with an already existing disease.

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    Cigarettes paralyze bronchi

    Glimmerstängel harm the body in many ways: Thus, the harmful smoke affects the cleaning function of the mucous membranes.On the mucous membrane of the bronchi, the movement of the cilia is paralyzed. Dirt particles and pathogens can then be transported worse to the outside. Smokers also carry a higher risk of serious complications if they already have an infection.

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