Immune System Development Health Article

Definition

The child's immune system is an intricate network of interdependent cell types, substances, and organs that collectively protect the body from bacterial, parasitic, fungal, viral infections, and tumor cells.

Description

The immune system was not recognized as a functional unit of the body until the late twentieth century, probably because its parts are not directly connected to each other and are spread in different parts of the body.

Organs of the immune system

The immune system contains the following organs and cells: tonsils and adenoids; the thymus gland; lymph nodes; bone marrow; and white blood cells that leave blood vessels and migrate through tissues and lymphatic circulation. The spleen, appendix, and patches of lymphoid tissue in the intestinal tract are also parts of the immune system.

The essential job of this system is to distinguish self-cells from foreign substances and to recognize and take protective action against any materials that ought not to be in the body, including abnormal and damaged cells. The immune system can seek out and destroy disease germs, infected cells, and tumor cells. The immune system includes the following cells:

• T lymphocytes (T cells)
• B lymphocytes (B cells)
• natural killer cells (NK cells)
• dendritic cells
• phagocytic cells
• complement proteins

These cells develop from "pluripotential hematopoietic stem cells" starting from a gestational age of about five weeks. They circulate through various organs in the lymphatic system as the fetus develops. T and B lymphocytes are the only units of the immune system that have antigen-specific recognition powers; they are responsible for adaptive immunity. In other words, the T and B cells are important in the immunity that vaccination promotes.

How immunity works

The lymphatic system is a key participant in the body's immune actions. It is a network of vessels and nodes unified by the circulatory system. Lymph nodes occur along the course of the lymphatic vessels and filter lymph fluid before it returns to the bloodstream. The system removes tissue fluids from intercellular spaces and protects the body from bacterial invasions.