Today we will tell you about what the thymus (thymus gland) is. In addition, you will find out how the mentioned body looks, what functions it performs and where it is located.
General information
Thymus (thymus gland) is an organ of lymphopoiesis in humans, as well as in many animals. In it, immunological “learning” occurs, the maturation and differentiation of T cells of the immune system.
The appearance of the body
Thymus (thymus gland) is a small-sized organ of soft consistency, which has a pinkish-gray color, and has a lobed surface. In newborn babies, its dimensions are about 4 cm in width, 5 in length and 6 in thickness. Thymus in children can be weighing 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 mass can be 20-38 grams.
With age, the thymus (thymus gland) can undergo atrophy, and in old age it can hardly differ from the surrounding fatty tissues. At 75, the mass of such an organ is only 6 grams. In addition, he is losing his 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
Thymus is located in the highest region of the chest. He is hiding right behind the sternum. In front of it, the sternum body adjoins to the level of the 4th costal cartilage, as well as the handle. 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, touch it behind. On the sides there is a mediastinal pleura.
Organ structure
Now you know what the thymus is. The structure of this body we will consider right now. In humans, it consists of 2 lobes fused to each other or tightly fitting. The lower part of the thymus is wide, and the upper, on the contrary, is very narrow. The upper pole of this organ strongly resembles a double-toothed fork. Actually, hence its name.
Absolutely the whole organ is covered with a special capsule, which consists of dense tissue (connective). Lintels extend from it into the depths. It is they who divide the thymus into lobules.
Lymphatic drainage, blood supply and innervation
The blood supply to 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 lower and upper thyroid arteries. As for the venous outflow, it is carried out along the branches of the brachiocephalic and internal chest veins.
Lymph from the thymus flows into the 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 sympathetic, which originate from the stellate nodes of the sympathetic and upper thoracic trunk, which are part of the nerve plexuses surrounding the vessels supplying the organ.
Tissue structure
The stroma of the thymus gland consists entirely of epithelium. Diverticuli originate from the 3rd branchial 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 migrated to this organ from the liver. As a rule, this happens in the first, second trimester of pregnancy.
First of all, proliferation of different blood cells occurs in the thymus gland 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, cerebral and cortical matter are distinguished. The latter is located on the periphery and looks like a dark spot. There are also blood capillaries and arterioles in the cortical substance.
It should be especially noted that this component contains cells:
- hematopoietic lymphoid row (i.e., T-lymphocytes mature);
- hematopoietic macrophage series (interdigitating and dendritic cells, typical macrophages).
In addition, the cortical substance includes cells of epithelial origin, which include:
- stellate (secrete 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);
- nanny cells with invaginations where lymphocytes develop.
T-lymphoblasts (fissile) predominate under the capsule of this organ. More mature are the maturing T-lymphocytes, which gradually migrate to the medulla. It should be noted that their maturation takes about 20 days. During this period, 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, coreceptors, and TCR begin to be selected.
The next step is the selection of negative lymphocytes. It flows right on the border with the brain element. Cells of monocytic origin begin to select lymphocytes, which are capable of interacting with the antigens of the body, and then trigger their apoptosis.
It should be noted that the brain substance contains mainly T-lymphocytes (ripening). It is from here that they enter 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 Gassal's corpuscles and efferent lymphatic vessels.
Thymus: features
Why is this organ necessary and what function does it perform in the body? Thymus hormones such as thymalin, thymosin, thymopoietin, thymic humoral factor and insulin-like growth factor-1 are polypeptides. If a person will experience hypofunction of the thymus gland, then he 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 properties in the thymus that provide protection against cells that become foreign to the body (due to various injuries). The early loss of the basic functions of the thymus gland can entail the defective functioning of the human immune system.
Epithelial cells of all lobes of the thymus produce a hormone that regulates the conversion of lymphocytes in the very mentioned organ. In some cases, at a more advanced age, a special deviation in immunity may be observed. As a rule, this is due to a pathological change in the thymus, as well as other lymphoid organs. Such a deviation may well cause a sudden death of the patient during anesthesia during surgery.
Experts say that the thymus is a certain central organ of the human immune system.
Regulation
Thymus hormones and their secretion is regulated by glucocorticoids, that is, the so-called hormones of the adrenal cortex. 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:
- Di George 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 thymic epithelial cells;
- 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 with subsequent instant transformation into leukemia;
- rare tumors (of nervous and vascular origin).
It should also be noted that thymic tumors can be a manifestation of type 1 endocrine neoplasia syndrome.
Who should I contact for examination?
If there is a suspicion that pathological changes in the thymus gland occur, then you should immediately visit an immunologist and oncologist. Based on the data of MRI, CT and X-rays of the organs of the chest cavity, doctors can make the patient the correct diagnosis and prescribe treatment (conservative or surgical).