The Immune System
Our bodies are continuously bombarded by a variety of infectious pathogens including but not limited to bacteria, fungi, molds, parasites, spores, and viruses. Many of these circulate in the atmosphere as airborne matter. Their concentrations and varieties can vary regionally in any country or clime. But they are also normal inhabitants of the skin, the mouth, the respiratory passages, the GI tract, the urinary tract, and the lining membranes of the eyes. They regularly compromise physiological functions of the cells, tissues, and organs, but when invading deeper body tissues en masse they can and do cause serious pathological conditions including morbidity and mortality.
Our body's main defenses against pathogens are circulating white blood cells (leukocytes, also called WBCs) and residential tissue cells that are derived from WBCs such as tissue macrophages. These systems work in coordination by ingesting and destroying foreign materials through phagocytosis and by creating antibodies and sensitized lymphocytes that can either inactivate or destroy the invaders.
Immune implies to defend against infection either by specific or nonspecific mechanisms. The word also has general reference to the immune system or to an immune response. One can refer to any good medical dictionary or textbook of immunology and find tables of immunodeficient disorders, diseases, and syndromes. Additionally, the molecular names and structures of the various immunoglubulins in our blood can be found in such books.
Leukocytes are the body's mobile units of defense. They are formed in the bone marrow but also in the lymphatic system. This is one of the needs for healthy bone marrow and healthy lymphatics. The two leukocyte-forming tissues