Today we will tell you about what is the thymus (thymus gland). In addition, you will learn how the mentioned organ looks like, what functions it performs and where exactly it is located.
General information
Thymus (thymus gland) is the organ of lymphopoiesis in humans, as well as in many animals. Immunological "learning", maturation and differentiation of T-cells of the immune system take place in it.
Appearance of the organ
Thymus (thymus gland) is a small organ of soft consistency, having a pinkish-gray color, with a lobed surface. In newborn babies, its dimensions are approximately 4 cm in width, 5 in length and 6 in thickness. The thymus in children can weigh 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 it practically does not differ from the fatty tissues surrounding it. At 75 years old, the mass of such an organis only 6 grams. In addition, it loses its color. This is due to an increase in fat cells and the proportion of stroma in it. So, the thymus becomes more yellow.
Thymus gland: location in the human body
The thymus is located in the uppermost region of the chest. It hides just behind the breastbone. In front of it, the body of the sternum adjoins to the level of the 4th costal cartilage, as well as the handle. From behind, it is touched by the upper region of the pericardium, which covers the initial sections of the pulmonary trunk and aorta, the left brachiocephalic vein and the aortic arch. On the sides is the mediastinal pleura.
Organ structure
Now you know what the thymus is. We will consider the structure of this organ right now. In humans, it consists of 2 lobes, fused with each other or tightly fitting. The lower part of the thymus is wide, while 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). Jumpers extend from it in depth. It is they who divide the thymus into lobules.
Lymphatic drainage, blood supply and innervation
The blood supply of this organ comes from the thymic branches of the aortic arch, the thoracic artery (internal), as well as the brachiocephalic trunk and the branches of the inferior and superior 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 intolymphatic parasternal and tracheobronchial plexuses.
The thymus gland (the function of this organ will be presented later) is innervated by the branches of the left and right vagus nerves, as well as the sympathetic ones, which originate from the stellate nodes of the sympathetic and upper thoracic trunk, which are part of the nerve plexuses surrounding the vessels feeding the organ.
The structure of tissues
The thymus stroma consists entirely of epithelium. Diverticula originate from the 3rd gill arch and then grow 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 have migrated to this organ from the liver. As a rule, this happens even in the first, second trimester of pregnancy.
First of all, the proliferation of different blood cells occurs in the thymus tissue. 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 medulla and cortex 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 especially noted that this component contains cells:
- hematopoietic of the lymphoid series (that is, T-lymphocytes mature);
- hematopoietic macrophages (interdigitating and dendritic cells, typical macrophages).
Besides this, cortic althe substance includes cells of epithelial origin, which include:
- star-shaped (secrete soluble thymus hormones - thymosin, thymopoietin and others that regulate the process of 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 the tissue is formed, and a hematothymic barrier is also formed);
- nanny cells that have invaginations where lymphocytes develop.
T-lymphoblasts (dividing) predominate under the capsule of this organ. More deeply are maturing T-lymphocytes, which gradually migrate to the medulla. It should be noted that their maturation takes about 20 days. During this period, the rearrangement and formation of genes encoding the T-cell receptor occurs. After that, they undergo selection (positive). In other words, when interacting with epithelial cells, only "suitable" lymphocytes, co-receptors and TCRs begin to be selected.
The next step 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 antigens of the body, and then trigger their apoptosis.
It should be noted that the medulla contains mainly T-lymphocytes (maturing). It is from here that they go into the bloodstream and settle throughout the body. The cellular composition of this substance is represented by stellate, supporting epithelial cells and macrophages. In addition, there are Hassall's corpuscles and efferent lymphatic vessels.
Thymus: functions
What is this organ for and what function does it perform in the body? Thymus hormones such as thymalin, thymosin, thymopoietin, thymus humoral factor and insulin-like growth factor-1 are polypeptides. If a person has hypofunction of the thymus gland, then his immunity will noticeably decrease due to a decrease in the number of T-lymphocytes in the blood.
Thus, we can safely say that T-lymphocytes acquire properties in the thymus that provide protection against cells that become foreign to the body (due to various damage). An early loss of the basic functions of the thymus gland can lead to a defective functioning of the human immune system.
Epithelial cells of all lobes of the thymus produce a hormone that regulates the transformation of lymphocytes in the organ itself. In some cases, at a more mature age, there may be a particular deviation in immunity. As a rule, this is associated with a pathological change in the thymus, as well as other lymphoid organs. Such a deviation may well be the cause of the sudden death of the patient during anesthesia for surgical intervention.
Experts say that the thymus is a kind of central organ of the human immune system.
Regulation
Thymus hormones and their secretion are regulated by glucocorticoids, that is, the so-called cortical hormonesadrenal glands. In addition, interferons, lymphokines and interleukins produced by other cells of the immune system are responsible for the function of this organ.
Possible diseases of the thymus
This body may be subject to deviations such as:
- DiGeorge syndrome;
- Medak syndrome;
- myasthenia gravis (develops as an independent disease, but quite often associated with thymoma).
In addition, in the presented organ, the appearance of tumors such as:
- thymoma, formed from thymic epithelial cells;
- T-cell lymphoma, formed from lymphocytes, as well as their precursors;
- neuroendocrine tumors;
- pre-T-lymphoblastic tumors, which sometimes have a primary localization in the thymus and are detected as a massive infiltrate in the mediastinum, followed by immediate transformation into leukemia;
- rare tumors (of nervous and vascular origin).
It should also be noted that thymus tumors may be a manifestation of endocrine neoplasia type 1 syndrome.
Who should I contact for an examination?
If there is a suspicion that pathological changes are occurring in the thymus gland, then you should immediately visit an immunologist and an oncologist. Based on MRI, CT and X-ray data of the chest cavity, doctors can make a correct diagnosis for the patient and prescribe treatment (conservative or surgical).
