Thymus (thymus gland). Thymus is a structure. Thymus gland - location

Today we will tell you about the thymus (thymus gland). In addition, you will learn how to iron out the body, what functions it performs and where it is located.

General information

Thymus (thymus gland) is the organ of lymphopoiesis of humans, as well as many animals. It involves immunological "training", maturation and differentiation of the T-cells of the immune system.

Appearance of the organ

Thymus (thymus gland) is a small organ of a soft consistency, having a pinkish gray color and having a lobed surface. In newborn infants, its size is about 4 cm in width, 5 - in length and 6 - in thickness. Thymus in children can be about 15-17 grams.

The growth of this organ continues until the very beginning of puberty. During this period, its dimensions reach such maximum values: up to 7.5 cm in width and up to 16 - in length. Its weight can be 20-38 grams.

With age, the thymus (thymus gland) can undergo atrophy, and in old age practically does not differ from the surrounding fatty tissues. In 75 years the weight of such an organ is only 6 grams. In addition, it loses its color. This is due to the increase in it fat cells and stromal proportion. So, the thymus becomes more yellow.

Thymus gland: location in the human body

The thymus is located in the uppermost region of the thorax. He hides behind the sternum. In front of it, the body of the sternum adjoins the level of the 4th costal cartilage, and also the handle. Behind it touch the upper region of the pericardium, which covers the initial sections of the pulmonary trunk and aorta, the left brachiocephalic vein and the arch of the aorta. The sides are mediastinal pleura.

Structure of the organ

Now you know what a thymus is. The structure of this body, we will consider right now. In man, it consists of two parts, joined to each other or tightly fitting. The lower part of the thymus is wide, and the upper part, on the contrary, is very narrow. The upper pole of this organ strongly resembles a two-pronged fork. Actually, hence its name.

Absolutely the entire organ is covered with a special capsule, which consists of a dense tissue (connective). From her in the depths of the jumper. They divide the thymus into lobules.

Lymph outflow, blood supply and innervation

The blood supply of this organ comes from the thymic branches of the arch of the aorta, the thoracic artery (internal), as well as the brachiocephalic trunk and branches of the lower and upper thyroid arteries. As for the venous outflow, it is carried out along the branches of the brachiocephalic and internal thoracic veins.

Lymph from the thymus flows into lymphatic parasternal and tracheobronchial plexuses.

The thymus gland is innervated (the function of this organ will be presented later) by the branches of the left and right vagus nerves, as well as by the sympathetic ones, which originate from the stellate nodes of the sympathetic and upper chest trunk, which are part of the nerve plexuses that surround the vessels feeding the organ.

Structure of tissues

The stroma of the thymus gland consists entirely of the epithelium. Diverticula originate from the 3rd gill arch, and then sprout into the anterior mediastinum. In some cases, the stroma of this organ is formed by additional strands (from the 4th pair of gill arches).

Lymphocytes are formed from blood stem cells that migrated to this organ from the liver. As a rule, this happens in the first, second trimester of pregnancy.

In the first place in the tissue of the thymus gland proliferation of different blood cells occurs. Although soon its function is reduced to the formation of T-lymphocytes. As mentioned above, the thymus has a lobed structure. In the tissues of these lobules, the cerebral and cortical substances are distinguished. The latter is located on the periphery and looks like a dark spot. Also in the cortex there are blood capillaries and arterioles.

It should be specially noted that this component contains cells:

• Hematopoietic lymphoid series (ie, mature T-lymphocytes);
• Hematopoietic macrophage series (interdigitating and dendritic cells, typical macrophages).

In addition, the cortex includes cells of epithelial origin, which include:

• Stellate (secretes the soluble hormones of the thymus - thymosin, thymopoietin and others, regulating the growth, differentiation and maturation of T cells, as well as the activity of more mature elements of the immune system).
• Supporting cells (due to them a "frame" of tissue is formed, and a hematotymic barrier is formed);
• "Nurse" cells with invaginations, where lymphocytes develop.

Under the capsule of this organ, T-lymphoblasts (dividing) predominate. Mature T-lymphocytes are located more deeply, which gradually migrate to the brain substance. It should be noted that their maturation takes about 20 days. During this period, the genes encoding the T-cell receptor are rearranged and formed. After that they undergo selection (positive). In other words, when interacting with epithelial cells, only "suitable" lymphocytes, co-receptors and TCR are selected.

The next stage is the selection of lymphocytes negative. It flows right on the border with the brain element. Cells of monocytic origin begin to select lymphocytes that are capable of interacting with the body's antigens, and then trigger their apoptosis.

It should be noted that the brain substance contains mainly T-lymphocytes (ripening). It is from here that they go into the bloodstream and settle in the body. The cellular composition of this substance is represented by stellate, supporting epithelial cells and macrophages. In addition, there are bodies of Hassala and vascular lymphatic vessels.

Thymus: functions

What is this body needed for and what function does it perform in the body? Thymus hormones such as thymine, thymosin, thymopoietin, thymus humoral factor and insulin-like growth factor-1 are polypeptides. If a hypothyroidism of the thymus gland is observed in a person, then it will noticeably decrease immunity due to a decrease in the number of T-lymphocytes in the blood.

Thus, it can be safely noted that T-lymphocytes acquire in the thymus such properties that provide protection against cells becoming alien to the body (due to various injuries). The early loss of the basic functions of the thymus gland can lead to an inferior functioning of the human immune system.

Epithelial cells of all thymus shares produce a hormone regulating the transformation of lymphocytes in the very organ mentioned. In some cases, at a more mature age, there may be a special deviation in immunity. Typically, this is due to a pathological change in the thymus, as well as other lymphoid organs. Such a deviation may well lead to a sudden death of the patient during anesthesia during surgery.

Experts say that the thymus is a central organ of the human immune system.

Regulation

Thymus hormones and their secretion are regulated by glucocorticoids, that is, the so-called hormones of the adrenal cortex. In addition, interferon, lymphokines and interleukins produced by other cells of the immune system are responsible for the function of this organ.

Possible diseases of thymus

This body may be subject to such deviations as:

• Di Giorgie's syndrome;
• Medak syndrome;
• Myasthenia gravis (develops as an independent disease, but is often associated with thymoma).

In addition, in the presented organ, the occurrence of such tumors as:

• Thymoma, formed from epithelial cells of the thymus;
• T-cell lymphoma formed from lymphocytes, as well as their predecessors;
• Neuroendocrine tumors;
• Pre-T-lymphoblastic tumors, which sometimes have primary localization in the thymus gland and are detected as a massive infiltrate in the mediastinum followed by an immediate transformation into leukemia;
• Rare tumors (of nervous and vascular origin).

It should also be noted that tumors of the thymus may be a manifestation of the syndrome of endocrine neoplasia of the 1st type.

To whom to address for inspection?

If there is a suspicion that there are pathological changes in the thymus gland, then immediately visit the immunologist and oncologist. Based on the data of MRI, CT and X-ray of chest organs, doctors can give the patient a correct diagnosis and prescribe treatment (conservative or operative).