Anatomy and Disorders of the Immune System
The immune system functions as the body’s defense mechanism against invasion. The term immunity refers to the body’s specific protective response to an invading foreign agent or organism. Immune function is affected by age and by a variety of other factors, such as,
• Central nervous system function
• Emotional status
• The stress of illness
Dysfunctions involving the immune system occur across the life span. Many are genetically based; others are acquired.
The term immunopathology refers to the study of diseases resulting from dysfunctions within the immune system. Disorders of the immune system may stem from excesses or deficiencies of immunocompetent cells, alterations in the function of these cells, immunologic attack on self-antigens, or inappropriate or exaggerated responses to specific antigens.
To gain insight into immunopathology and the growing number of immunologic-based disorders and to assess and care for people with immunologic disorders, the nurse needs a sound knowledge base of the immune system and how it functions.
ANATOMY OF THE IMMUNE SYSTEM
The immune system comprises cells and molecules with specialized roles in defending against infection and invasion by other organisms. Its major components include the bone marrow, the white blood cells (WBCs) produced by the bone marrow, and the lymphoid tissues. Lymphoid tissues include the thymus gland, the spleen, the lymph nodes, the tonsils and adenoids, and similar tissues in the gastrointestinal, respiratory, and reproductive systems.
The bone marrow is the production site of the WBCs involved in immunity. Like other blood cells, lymphocytes are generated from stem cells, which are undifferentiated cells. Descendants of stem cells become lymphocytes, the B lymphocytes (B cells), and the T lymphocytes (T cells. B lymphocytes mature in the bone marrow and then enter the circulation. T lymphocytes move from the bone marrow to the thymus, where they mature into several kinds of cells capable of different functions.
The spleen, composed of red and white pulp, acts somewhat like a filter. The red pulp is the site where old and injured red blood cells are destroyed. The white pulp contains concentrations of lymphocytes. The lymph nodes are distributed throughout the body. They are connected by lymph channels and capillaries, which remove foreign material from the lymph before it enters the bloodstream.
The lymph nodes also serve as centers for immune cell proliferation. The remaining lymphoid tissues, such as the tonsils and adenoids and other mucoid lymphatic tissues, contain immune cells that defend the body’s mucosal surfaces against microorganisms.
Immune System Disorders:
Immune System has five common Disorders include:
• Autoimmunity: Normal protective immune response paradoxically turns against or attacks the body, leading to tissue damage.
• Hypersensitivity: Body produces inappropriate or exaggerated responses to specific antigens
• Gammopathies: Immunoglobulins are overproduced.
• Immune deficiencies Primary: Deficiency results from improper development of immune cells or tissues, usually with a genetic basis.
• Secondary Immune Deficiencies: Deficiency results from some interference with an already developed immune system.
How Immune System Responses and Defenses:
There are two general types of immunity: natural (innate) and acquired (adaptive).
• Natural immunity is a nonspecific immunity present at birth.
• Acquired or specific immunity develops after birth.
Natural immune responses to a foreign invader are very similar from one encounter to the next regardless of the number of times the invader is encountered; in contrast, acquired responses increase in intensity with repeated exposure to the invading agent. Although each type of immunity plays a distinct role in defending the body against harmful invaders, the various components usually act in an interdependent manner.
Natural (innate) immunity provides a nonspecific response to any foreign invader, regardless of the invader’s composition. The basis of natural defense mechanisms is the ability to distinguish between friend and foe or “self” and “nonself.” Such natural mechanisms include physical and chemical barriers, the action of WBCs, and inflammatory responses.
- PHYSICAL AND CHEMICAL BARRIERS:
Physical surface barriers include intact skin and mucous membranes, which prevent pathogens from gaining access to the body, and the cilia of the respiratory tract along with coughing and sneezing responses, which act to filter and clear pathogens from the upper respiratory tract before they can invade the body further.
Chemical barriers, such as acidic gastric secretions, mucus, enzymes in tears and saliva, and substances in sebaceous and sweat secretions, act in a nonspecific way to destroy invading bacteria and fungi. Viruses are countered by other means, such as interferon. Interferon, one type of biologic response modifier, is a nonspecific viricidal protein naturally produced by the body that is capable of activating other components of the immune system.
Acquired (adaptive) immunity—immunologic responses acquired during life but not present at birth—usually develops as a result of prior exposure to an antigen through immunization (vaccination) or by contracting a disease, both of which generate a protective or vaccine, the body produces an immune response that is sufficient to defend against the disease upon re-exposure to it.
The two types of acquired immunity are known as active and passive.
Active acquired immunity, the immunologic defenses are developed by the person’s own body. This immunity generally lasts many years or even a lifetime.
Passive acquired immunity is temporary immunity transmitted from another source that has developed immunity through previous disease or immunization. For example, immune globulin and antiserum, obtained from the blood plasma of people with acquired immunity, are used in emergencies to provide immunity to diseases when the risk for contracting a specific disease is great and there is not enough time for a person to develop adequate active immunity.
Response to Invasion:
When the body is invaded or attacked by bacteria, viruses, or other pathogens, it has three means of defending itself:
• The phagocytic immune response
• The humoral or antibody immune response
• The cellular immune response