The Immune System

Health Matters – The Body’s Defence System

What is the immune system?

The immune system protects the body from infection by pathogenic organisms. It is composed of a complex constellation of cells, organs and tissues, arranged in an elaborate and dynamic communications network. The immune system is, in its simplest form, a cascade of detection and adaptation, culminating in a system that is remarkably effective.


The immune system protects the body from infection by creating and maintaining barriers that prevent bacteria and viruses from entering the body. If a pathogen breaches the barriers, and gets into the body, the innate immune system is equipped with specialized cells that detect, and often eliminate, the invader before it is able to reproduce, potentially causing serious injury to the host. A pathogen that successfully evades the innate immune cells faces a second, adaptive immune system. It is through the adaptive response that the immune system gains the ability to recognize a pathogen, and to mount stronger attacks each time that pathogen is encountered.

Surface Barriers

Several barriers protect the host from infection; including mechanical, chemical and biological barriers.

The skin is a mechanical barrier and is often the first line of defense against infection. The skin is made up of the epidermis, outer layer, and dermis, and most infectious agents find it to be impenetrable.Coughing and sneezing causes tiny hairs, called cilia, to move in an upward motion mechanically ejecting both living things and other irritantsfrom the respiratory tract. The flushing action of saliva, tears, and urine also mechanically expel pathogens, while mucus secreted by the respiratory and gastrointestinal tract serves to protect the host by trapping microorganisms

The skin is comprised of tightly packed cells rich in keratin, this serves as a chemical barrier, because it impedes water and is slightly acidic, which inhibit bacterial growth. Enzymes, in saliva and tears and breast milk are antibacterial. Gastric acid, the low pH and destructive enzymesthat exist in the stomach, are powerful chemical defenses against ingested pathogens.

Within the intestines, commensal flora serve as biological barriers by competing with pathogenic bacteria for food and space, diminishing the probability that pathogens will be able to reach sufficient numbers to cause illness. Antibiotics do not discriminate between pathogenic bacteria and the normal gut flora, and ingestion of oral antibiotics can sometimes lead to an “overgrowth” of fungus (fungus is not affected by antibiotics), such as a yeast infection.

If microorganisms successfully breach the surface barriers, the cells and mechanisms of the innate immune system are present, and ready to be mobilized to defend the the host. Innate immune defenses are non-specific, meaning that the innate system recognizes and responds to, pathogens in a generic way. The innate system does not confer long-lasting or protective immunity to the host. It is thought to constitute an evolutionarily older defense strategy, and is the dominant system of host defense in fungi, insects, and in primitive multicellular organisms. The innate immune system protects the host by establishing humoral, chemical and cellular barriers to infection.

Humoral and chemical barriers” Humoral and chemical barriers Inflammation Inflammation, characterized by redness and swelling, is one of the first responses of the immune system to infection or irritation. Inflammation is stimulated by chemical factors, including specialized chemical mediators, called cytokines, released by injured cells and serves to; establish a physical barrier against the spread of infection, and to promote healing of any damaged tissue following the removal of pathogens.1

Ultradistance running and the immune system

“In general, the literature suggests that acute exercise—for example, marathon and ultramarathon running—results in an associated reduction in aspects of immune competence so that such athletes may be at increased risk of illness and need to pay particular attention to their nutritional state, hygiene, and exposure to infections.2″

1 Wikipedi

2 Shephard RJ, Shek PN. Immune responses to inflammation and trauma: a physical training model. Can J Physiol Pharmacol 1998;76:469–72. The home of multiday running news and events.

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