Defense Mechanisms of the Host in perspective
The First Line of Defense: is a surface protection composed of anatomical and physiological barriers that keep microbes com penetrating sterile body compartments. It includes physical barriers, chemical barriers, and genetic barriers.
The Second Line of Defense: is a cellular and chemical system that comes immediately into play if infectious agents make it past the surface defenses. Examples include phagocytes that engulf foreign matter and destroy it, and inflammation which holds infections in check. It includes inflammatory response, interferons, phagocytosis, and complement.
The Third Line of Defense: specific host defenses that must be developed uniquely for each microbe through the action of specialized white blood cells. This form of immunity is usually long term and has memory. It includes antibodies, t cells, accessory cells and cytokines.
The Second Line of Defense: is a cellular and chemical system that comes immediately into play if infectious agents make it past the surface defenses. Examples include phagocytes that engulf foreign matter and destroy it, and inflammation which holds infections in check. It includes inflammatory response, interferons, phagocytosis, and complement.
The Third Line of Defense: specific host defenses that must be developed uniquely for each microbe through the action of specialized white blood cells. This form of immunity is usually long term and has memory. It includes antibodies, t cells, accessory cells and cytokines.
The Body is partitioned into several fluid-filled spaces called the intracellular, extracellular, lymphatic, cerebrospinal, and circulatory compartments. Although these compartments are physically separated, they have numerous connections. Their structures and position permit extensive interchange and communication. Among the body compartments that participate in immune function are
- the reticuloendothelial system
- the spaces surrounding tissue cells that contain extracellular fluid
- the bloodstream, and
- the lymphatic system
Reticuloendothelial system-is intrinsic to the immune function because it provides a passageway within and between tissues and organs. It also coexists with and helps form a niche for a collection of phagocytic cells termed the mononuclear phagocyte system.
Extracellular Fluid- compartment that surrounds all tissue cells and is penetrated by both blood an lymph vessels, which bring all components of the second and third line of defense to attack infectious microbes.
The blood contains both specific and nonspecific defenses. Nonspecific cellular defenses include the granulocytes, macrophages, and dendritic cells. The two components of the specific immune response are the T lymphocytes, which provide specific cell-mediated immunity, and the B lymphocytes, which produce specific antibody or humoral immunity.
Extracellular Fluid- compartment that surrounds all tissue cells and is penetrated by both blood an lymph vessels, which bring all components of the second and third line of defense to attack infectious microbes.
The blood contains both specific and nonspecific defenses. Nonspecific cellular defenses include the granulocytes, macrophages, and dendritic cells. The two components of the specific immune response are the T lymphocytes, which provide specific cell-mediated immunity, and the B lymphocytes, which produce specific antibody or humoral immunity.
The Lymphatic System has three functions:
- It returns tissue fluid to general circulation
- it carries away excess fluid in inflamed tissues
- it concentrates and processes foreign invaders and initiates the specific immune response.