Lymphoid tissue (synonym lymphatic tissue) is a collective term for the structures in which lymphocyte formation occurs. Human lymphoid tissue is about 1% of body weight and is one of the most important components of lymphoid organs. These include lymph nodes (see Lymphatic system ), spleen (see), thymus (see), tonsils (see). In the mucous membrane of the digestive tract, the lymphoid tissue is represented by single lymphatic follicles, which are grouped together (Peyer's patches), and there are an especially large number of them in the walls of the appendix . Areas of lymphoid tissue are located in the mucous membrane of some organs (bronchi, urinary tract, kidneys).
One of the main functions of the lymphoid organs is their participation in the processes of blood formation (lymphopoiesis). Lymphocytes (see) are able, moving amoeboidly, to pass through the vascular wall and phagocytize, and also give rise to various types of cellular forms, including plasma cells (see Connective tissue ), which are involved in the production of antibodies. With this ability of lymphocytes, an important function of the lymphoid tissue is associated — its participation in the body’s defense reactions. In chronic inflammatory processes, foci of lymphoid tissue appear in various organs.
Lymphoid tissue is very sensitive to external and internal influences. So, under the influence of X-rays, lymphocytes die quickly. With the introduction of thyroid hormones lymphoid tissue expands. Adrenal hormones have a great influence on the development of lymphoid tissue. Inadequate function of the adrenal cortex causes the growth of lymphoid tissue. Introduction of adrenal hormones leads to degeneration of lymphoid tissue and death of lymphocytes.