The immune system is an important defense system in the body and consists of lymphoid organs, lymphoid tissues, immune cells and immunoactive substances.

immune defense

immune surveillance

Immune stability

(1) Classification of lymphocytes

(2) Functional characteristics of lymphocytes

(3) Lymphocyte recycling

It is diffusely distributed with no obvious boundaries with other surrounding tissues and contains T cells and a small amount of B cells.

In addition to general capillaries and lymphatic capillaries, there are also postcapillary venules in tissues, which are important channels for lymphocytes to enter lymphatic tissue from the blood.

When stimulated by antigen, diffuse lymphoid tissue becomes dense and expanded, and lymph nodes appear.

It is often located in diffuse lymphoid tissue and has clear boundaries with surrounding tissues.

Lymph nodes contain a large number of B cells and a certain amount of Th cells, follicular dendritic cells, macrophages, etc.

After being stimulated by antigen, the lymph node increases in size, and a lightly stained area appears in the center of the node, called the germinal center, forming the stimulated lymph node. Lymph nodes without germinal centers are smaller and are called primary lymph nodes

Lymph nodes are important morphological markers reflecting humoral immune response

The thymus and bone marrow are the places where lymphocytes are cultivated. Lymphoid hematopoietic stem cells form initial T cells in the thymus and initial B cells in the bone marrow.

These cells migrate to peripheral lymphoid organs and lymphoid tissues weeks before birth, and their occurrence and function are not affected by antigenic stimulation.

Including lymph nodes, spleen and tonsils, etc.

Peripheral lymphoid organs develop later than central lymphoid organs and develop fully after several months after birth.

2. Lymph nodes