Maintaining a healthy body is a complicated process. Over millions of years, humans have developed a sophisticated system to guard against harmful microorganisms such as bacteria, viruses, fungi, parasites, and pathogens. This bodily defense is called the immune system.
Before a microorganism can enter the body, it must first get past a number of natural barriers. These include obvious barriers such as skin, eyes, nose, and mouth. Skin secretes antibacterial substances, while tears and mucus secret an enzyme that breaks down bacteria. Saliva is also anti-bacterial, while stomach acids take care of organisms that may be ingested.
How the Immune System Protects
The immune system protects the body in four basic ways: Creating a barrier between microorganisms and the body. Detecting and eliminating bacteria and viruses before they have a chance to proliferate. Eliminating bacteria and viruses that have managed to cause problems. Finding and eliminating cancerous and other unwanted cells
Most microorganisms do not get past that first line of defense. For example, cilia in the respiratory tract constantly move mucus and contaminants upward and out to prevent them from lodging in the lungs. Some, however, do manage to get past the front lines. This results in common bacterial and viral illnesses, which must run their course until the body builds immunity and recovers.
Macrophages, specialized cells produced by bone marrow confront viruses or bacteria that gets past the initial barriers. This confrontation may occur at an open wound or the substance may be carried to the nearest lymph node, which act as clearinghouses in the immune system.
If an unknown bacteria enters the body, a polymorphonuclear (PMN) leukocyte is called in by the immune system. PMNs completely engulf invading bacteria, as well as any surrounding debris.
When a macrophage encounters a virus, a similar process occurs. The virus is passed to a T cell where it is assessed. B cells are also called to help. Both types of cells have checklists which appear as receptors on their surfaces. Viruses and other substances that do not fit exactly into these receptors are considered dangerous. The T or B cells then commit the genetic identification of the invader to the immune system's memory so this particular invader will be banned, thus creating immunity.
Immune System Components
Major components of the immune system include the following:
Antibodies, also known as immunoglobulins and gammaglobulins are produced by white blood cell and respond to bacteria, viruses, and toxins. They can bind to these, disabling their actions or signaling that an invader needs to be removed.
Bone marrow produces red and white blood cells, all of which come from stem cells. They are called stem cells because they are precursors to different cell types and can branch off, changing into specific types of blood cells as needed.
The complement system is a mixture of proteins that activates when invaders get through the immune system's barriers. Only a handful of proteins, manufactured in the liver make up the complement system. These proteins work with antibodies, signaling that invading cells need to be removed.
Additional Immune System Helpers
Hormones-The immune system generates several hormones, including adrenaline, which actually suppresses immune system function. Tymosin encourage lymphocyte production. Interleukin is produced by macrophages after eating foreign cells. Macrophages also produce Tumor Necrosis Factor (TNF) which kills tumor cells and promotes the production of new blood vessels.
Lymph System-This is the clear, watery fluid that comes from blood. The lymph system detects bacteria and waste, taking them to the lymph nodes for processing and removal. Lymph nodes are filters that trap foreign bodies and can become swollen when fighting an infection. Lymph organs include tonsils, adenoids, the appendix, and clumps of tissue in the small intestine known as Peyer's patches.
Spleen-This organ filters the blood of foreign cells, as well as old red blood cell that need replacement. It contains two main types of tissue: one that disposes of worn-out blood cells, and another that contain lymphoid tissue.
As previously noted, immunity is acquired when T and B cells commit an invader to genetic memory, not allowing it to gain hold in the body. Immunizations work with the body's natural defenses by introducing weakened or killed forms of a disease-causing agent, thereby activating the immune response without the discomfort and risks associated with having the disease.
Conversely, some parts of the immune system weaken with age, resulting in greater risk of some diseases. That's why influenza and pneumococcal disease s more dangerous in the elderly, or in individuals with heart problems, diabetes, asthma, or other conditions that make it more difficult to overcome the invading microorganism.