See also: thyme - plant -

Thyme is a gland belonging to the lymphatic system and, more generally, to the immune system. It is an unequal organ, located in the upper part of the anterior mediastinum between the sternum and the large vessels that come out of the heart.

The function of the thymus is to bring various types of lymphocytes to maturation, finalizing them to destroy the intracellular pathogens. These cells, produced by the bone marrow in the form of immature precursors, undergo a series of transformations becoming first thymocytes and then T lymphocytes (from Timo). Their activity is the basis of cell-mediated immunity, that is to say of that process whereby the body recognizes and destroys the infected cells sparing the healthy ones. When a lymphocyte escapes this control, acquiring the ability to attack the human body's own antigens, it is eliminated by apoptosis; an alteration of this regulatory mechanism explains the involvement of the thymus in the pathogenesis of some autoimmune diseases, such as myasthenia gravis.

Once "trained", the T lymphocytes do not remain in the thymus, but migrate to other peripheral lymphatic organs (lymph nodes, spleen, tonsils, etc.) where they multiply to fully perform their defensive role.

The thymus is a highly vascularized organ and consists of two lobes. Each lobe is wrapped in a fibrous capsule that penetrates dividing it into numerous lobules. Inside they recognize a dark peripheral part, called cortex, and a lighter inner part, called medulla. The cortical portion is densely populated by immature lymphocytes, while the developed ones cluster in the inner part, where the cell population is much lower.

The activity and size of the thymus reaches their maximum expression at the beginning of the adolescent period, when the gland weighs about 30-40 grams. After this period, the thymus regresses slowly due to the action of the sex hormones and, a bit like the bone marrow present in the diaphyseal canal, is progressively replaced by adipose tissue (physiological atrophy). Once the development is over, the body has sufficient immune defenses to make up for the progressive involution of the thymus; if on the other hand the atrophy affects it prematurely the sensitivity to infections increases considerably.

The involution of the thymus is favored by excessive stress, while its immune function is supported by an adequate intake of vitamin A.

The thymus gland also produces peptide factors, sometimes classified as hormones, which influence the maturation of lymphocytes (thymosin, thymopoietin, timulin, interleukins). Thanks to these substances, the thymus would have an endocrine action, aimed at the development of lymphocytes in intra and extra-thymic sites.