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The Normal Flora

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  • The Normal Flora

    السلام عليكـــــــــــــــم !!!
    أزعجتني النورمال فلورا فلقيت شرح جمــيل عنها وقلـــــت الخير يعم فتقبلوا مني هذه المشاركة التي إستفدت منها أنا أول واحد !!!



    (تفضـــــــــــــــــلوا)....


    The Normal Flora of the Human Body

    What are the normal flora?

    It may or may not surprise you to find out that your body is host to billions of bacteria of many different kinds. These bacteria exist in many different parts of the body, and usually do not cause any problems for the host body. The following is a list of the main sites for bacteria that consitute the normal flora.
    The skin, especially the moist areas, such as the groin and between the toes.
    The respiratory tract, particularly the nose.
    Urinary tract.
    The digestive tract, i.e. the mouth, the terminal ileum and the colon.

    The normal flora of the digestive tract

    The stomach contains few bacteria because of its high acidity. Still there are some bacteria that survive there. Perhaps the most important of these is a recently discovered bacterium, Helicobacter Pylori, now known to be the cause of most (greater than 95%) cases of gastritis and peptic ulcers.

    The small intestine usually contains small numbers of Streptococci, Lactobacilli, and yeasts, particularly Candida Albicans. Larger numbers of these bacteria are found in the terminal ileum, the section of the small intestine just before the colon.

    The large intestine, or colon, is the main site for bacteria in the body. Roughly twenty percent of the faeces of a normal person consists of bacteria, most of which have come from the colon. The main bacteria in the colon are Bacteroides, Bifidobacterium, Eubacterium, Coliforms, Streptococcus, Lactobacillus and Clostridium.

    There are many different types of relationship that the body can have with the normal flora. These are

    Mutualism. In a mutualist relationship, both the host and the microbe benefit from the relationship. The best example if this is E.Coli. This organism lives in the intestines, where it receives nourishment, and in turn produces Vitamin K, which the human body requires for the process of blood clotting.

    Commensalism. A commensalist relationship is where one partner of the relationship benefits, and the other partner is neither benefitted nor harmed.

    Parasitism. A parasitic relationship is where one organism benefits at the expense of the host. The cost to the host can vary from slight to fatal. An external parasite (ectoparasite) is said to cause infestation, an internal parasite (endoparasite) is said to cause infection.

    Pathogenic. A pathogenic relationship is where an organism causes damage to the host during infection. An Opportunistic Pathogen causes disease in a host that is physically impaired or debilitated. Normally the opportunist organism is harmless, but it takes advantage when the hosts defences are impaired, for example when the normal flora have been destroyed by antibiotics, or when the immune system has been suppressed by drug treatment or by other illnesses.

    The relationships between the human host and most normal flora usually fall under the the category of Mutualist relationships. The benefit to the bacteria is that they have a place to survive and multiply. The benefits to the human host are as follows

    The hosts ability to nourish itself is increased. The bacteria may produce vitamins (such as B and K), and may break down food stuffs that are normally indigestible by the host into components that can be digested.
    The host is protected against infection by pathogenic organisms. This happens in several ways. Firstly, the normal flora occupy all of the available niches for bacteria, thus presenting the invading pathogen with the problem of finding somewhere to anchor itself. Secondly, the normal flora may outcompete the invader for the available food, thus starving the invader and preventing it from multiplying. Thirdly, some members of the normal flora produce antibacterial chemicals (bacteriocins) as a side product of their metabolism, thus generating a local antibiotic effect.


    Skin Flora

    The surface of the skin itself comprises several distinct environments. Areas such as the axilla (armpit), the perineum (groin) and the toe webs provide typically moister regions for bacterial growth. These "tropical forest" environments often harbor the largest diversity amongst the skin flora. Typical organisms include Staphylococcus aureus, Corynebacterium and some Gram-negative bacteria. The bulk of the human skin surface, however, is much drier and is predominantly inhabited by Staphylococcus epidermidis and Propionobacterium.

    Oral Cavity and Nasopharyngeal Flora

    Streptococci predominate in the oral cavity and nasopharyngeal regions but one can also find other anaerobes and species of Neisseria. Many potential pathogens may also be found in the nasopharynx of a healthy individual, providing a reservoir for infection of others. These pathogens include Streptococcus pneumoniae, Neisseria meningitidis and Haemophilus influenzae.
    Urogenital Flora

    The urogenital tract is normally sterile with the exception of the vagina and the distal 1 cm of the urethra. Various members of the genus Lactobacillus predominate in the vagina. These organisms generally lower the pH to around 4-5, which is optimal for the lactobacilli but inhibitory for the growth of many other bacteria. Loss of this protective effect by antibiotic therapy can lead to infection by Candida ("yeast infection"). The urethra may contain predominantly skin microorganisms including staphylococci, streptococci and diphtheroids
    .

    Are the normal flora always beneficial?

    The answer to this question is: definitely not! If they remain in the site with which they are usually associated, the normal flora are usually beneficial. However, some members of the normal flora are also opportunistic pathogens, or are pathogenic if they turn up at a site with which they are not normally associated. Bacteroides bacteria, which normally reside in the intestines, may produce abscesses if they penetrate into deeper tissues via traumatic or surgical wounds. E.coli, a normal inhabitant of the gastrointestinal tract, is the most common cause of urinary tract infections.

    Why do the normal flora not induce an immune response from the host?

    The short answer to this question is that they do. Antibodies to the normal flora exist in our bodies, but at lower concentrations than would exist for pathogenic bacteria. They provide a "sparring partner" for our bodies that keeps our immune systems in tune. The precise role that our immune systems take in regulating the populations of the normal flora is not known.


    وشكــــــــــــــــــــــــــــــــرااااا......... ....الخ
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    jooker

  • #2
    شكراً لنقلك

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    • #3
      شكرا على المعلومات المفيده ... و الخير اللى عم علينا ...

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        مع خالص الشكر والتقدير

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          جزاك الله خيرا
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