The human immune system is a series of defensive shields with which the body is equipped to repulse both outside attacks as well as any internal uprisings that occur within its organs, communications networks, or bloodstream. The immune system is a series of interdependent parts that begin at the surface of the skin. A number of the internal organs contribute to the function of these defenses. The lymph glands and the cardiovascular system are the means by which the active agents of the immune system are transported throughout the body. Immunology is the specialized scientific study of immune system function.
Immunity is a characteristic of the human body that is present through two general mechanisms. Innate immunity is the manner in which the response to certain types of threat is genetically determined. The components of the body that contribute to its innate immunity are those that work to prevent or repel the entry of foreign matter, including the skin, the lungs, and the mucus contained within them. Secretions such as tears, saliva, and vaginal discharges that remove potentially harmful organisms are a function of the innate immune system.
The second general aspect of human immunity is its acquired or adaptive nature. Lymphocytes are important cellular mechanisms that are created by the body for the purpose of adapting to the threats presented to the body. The immune system produces a number of specialty cells, known as antibodies, whose function is to target pathogens and build immunities.
The innate and the adaptive characteristics of the immune system do not operate in isolation from one another. The response to biological threat made against the body is often the subject of a two-tiered reaction, engaging both innate and adaptive responses.
The immune system has a number of weapons with which it will respond to a threat to the body's health. Antigens are any substances that are capable of eliciting an immune response from the body. Antigens may be such microscopic particles as a strain of dangerous bacteria or a virus; a nail or a sliver of wood that punctures the skin is also an antigen. Certain aspects of the immune system function as antigen specific, designed to combat a particular threat that is identified by the body.
Other immune system components are systemic, in that they operate by means of their recognition of certain types of potentially dangerous cells; when the cell is not recognized by the immune system, it is attacked and destroyed. Certain types of illnesses, such as multiple sclerosis, are conditions that affect the autoimmune system. These illnesses are progressive, as they direct the systemic parts of the immune system to attack themselves.
The third class of immune system response is built upon the memory of the immune system as it developed from the knowledge of a prior immune threat. When the immune system has been the subject of a previous attack by a foreign substance, it responds with a greater force to repel the invader on the next occurrence. Inoculation against disease, which involves the injection of a small amount of dangerous living bacteria into the body, is a preventative measure that permits the body to build a successful future defense mechanism against specific threats. Diseases such as poliomyelitis, or polio, are prevented in this fashion.
The blood circulating through the cardiovascular system has a number of immune system responsibilities. Blood is comprised of three major components with respect to immune function: plasma, which is approximately 90% water; erythrocytes (red blood cells) in an approximate volume of 5 million cells per mm3; and leukocytes (white blood cells), in a usual volume that ranges from 5,000 to 10,000 per mm3.
When blood volumes are low due to dehydration, the ability of the circulatory system to provide support to the immune system is reduced. Red blood cells are the transport mechanism for the cardiovascular system, particularly with respect to the delivery of oxygen and other nutrients essential to the production of energy. White blood cells are infection-fighting agents within the bloodstream and a backbone to the preservation of immunity; the generally fatal condition of leukemia is a cancer of the blood that occurs when the white cell production system self-destructs through the production of an abnormally high number of white blood cells.
The lymph system has two primary components: the first is the bone marrow, responsible for white
In the lymph nodes and elsewhere in the immune system are bacteria specially created by the body to consume potentially dangerous foreign bacteria. These eating substances, known as macrophage, attack antigens.
There are a number of other external factors that may influence the efficiency of the immune system. Stress has been proven to decrease immune function, as has the abuse of alcohol, the use of corticosteroids, and the ingestion of stimulants such as cocaine. Poor nutrition, either alone or in combination with insufficient exercise, will have a negative impact upon the immune system.