It defends the body against pathogenic microbes
and germs that are exposed to the human body everyday. The body’s defensive
mechanism is achieved through a series of steps called the immune response.

This attacks disease-causing microbes which are likely to invade the body’s
system. The immune system is also composed of specialised cells, various
tissues, organs and proteins that work together to protect the body. One of the
main cells involve in the body’s defensive activity is the white blood cells,
also known as leukocytes. These are produced in many parts of the body. The organs
and tissues involved in the immune system are called lymphoid organs which are;
spleen, bone marrow, thymus, appendix, lymph nodes, tonsils and the Peyer’s
patches found throughout the small intestinal duct. Primarily, leukocytes come
in two types; phagocytes and lymphocytes. The phagocytic cells chew harmful
microorganism whilst the lymphatic cells allow the body recognise previous
infectious microbes and help the body to destroy them. Lymphocytes also
consists of two types of cells; B- cells and T-cells. B-cells produce antibodies
to attack foreign antigens that causes harm to the body. T-cells, however, has
two main functions; to recognise and destroy malignant cells, and to orchestrate
an immune response which play a vital role in immunity.