Body defences

Respirable particles Particulate matter of such a size that it can pass through the body defences and into the lungs, where, depending on its nature, it will either deposit itself or be exhaled. 

If microorganisms are able to survive and grow within phagocytes then they will escape many of the other body defences and be distributed around the body. 

Antiseptic. This term means against sepsis which in general means wound infection. A bacteriostatic agent may prevent sepsis developing in the body especially if the normal body defences against sepsis are operative. For further details, see Chapter 10. 

In conclusion, the role of histamine H3 receptors in the immune responses has not yet been completely identified. The H3 receptor, located on mast cells, may represent a mechanism for a negative feedback through histamine autoregulation in tissue inflammation. The presence of this receptor on both mast cells and nerve endings suggests an important role for H3 receptors, especially when we consider that the immune system and the nervous system behave as separate arms of a unified, coordinated body defence system (McKay and Bienenstock, 1994). 

Many other applications for plasma polymers in the Life Sciences have been dted, often in relation to implantable medical devices or materials, with the goal of concealing the device from the bodies defence mechanisms, or improving cell colonisation of the material, e.g. endothelial cell growth into vascular grafts. A number of excellent studies from the group of Hans Griesser (CSIRO, Australia) describe the use of plasma polymers as substrates to which biomolecules can be immobilised. These immobilisations have been demonstrated to enhance the medium-term acceptability of contact lens materials and may prove relevant to implantable devices. 

Even if their absorption is high, the bioavailability of many compounds may be limited by an extensive metabolism that can affect the in vivo activity profile irrespective of its route of administration. Metabolism is vital since it transforms absorbed nutrients into endogenous substances required to maintain body functions for xenobiotics, including phytochemicals, metabolism represents the key body defence mechanism that converts them into less harmful, water-soluble, and thus excretable, compounds. Lipophilic, low molecular weight xenobiotics that are readily absorbed and distributed are difficult to eliminate and thus may accumulate to hazardous levels. Therefore, most lipophilic xenobiotics are metabolized into hydrophilic conjugates that are less likely to pass through membranes and, hence, can be more easily eliminated via the kidney. 

Main forms of chemical attack on the body toxic (including carcinogens), corrosive and dermatitic. Main routes of entry to absorbing areas absorption target organs and systems natural body defences. 

In addition to helping organisms adhere to surfaces (e.g. Streptococcus mutans and teeth) and protecting them from body defence mechanisms, such as the bactericidal action of serum or ingestion and killing by phagocytes (e.g. the pneumococci and Staphylococcus aureus) capsules probably protect cells from desiccation in natural environments which are prone to periodic drying. Their survival value to the cells therefore justifies the metabolic effort required for their production. 

Blood consists of about 55% plasma and 45% of formed elements, chiefly red corpuscles but also white corpuscles and platelets. The red corpuscles are mainly concerned with O2 and CO2 transport, the white corpuscles with body defence mechanisms and the platelets with the clotting process. 

For many of the drugs, however, the active constituents are not (yet) known the examination of their activity is thus often rendered more difficult in that experience of its administration over a long period of time is required. In these cases, it is often said that the drug concerned stimulates the body s own defence mechanisms formerly, the administration of such drugs was called nonspecific stimulant therapy, nowadays the concept of immunostimulation is used or paramunity inducers [I-6]. 

Primary irritants cause inflammation. Inflammation is one of the body s defence mechanisms. It is the reaction of a tissue to harm which is insufficient to kill the tissue and is typified by... 

Toxic reactions occur by several mechanisms activation of metabolism, production of reactive intermediates and subsequent reactions with cell macromolecules, changing receptor responses, or through abnormal defence reactions. Several compounds cause toxicity by mimicking the organism s own hormones or neurotransmitters, or activating the body s endogenous receptors in some non-physiological way. ... 

Respirable particulates Particulates in the size range that can pass through the defence mechanisms in the human body and enter the lungs during inhalation. 

A recent review [5] concluded that there is little convincing evidence that vitamin E increases antioxidant defences in the body. This would also question a benefit of vitamin E in the prevention and management of the diseases mentioned above. 

Primary irritants cause inflammation. Inflammation is one of the body s defence mechanisms. It is the reaction of a tissue to harm which is insufficient to kill the tissue and is typified by constriction of the small vessels in the affected area, dilation of the blood vessels, increased permeability of the vessel walls, and migration of the white blood and other defensive cells to the invading harmful chemical. The aim is to concentrate water and protein in the affected area to dilute the effect and wash away the chemical. Production of new cells is speeded up and contaminated surface cells are shed. 

The body possesses an efficient natural defence mechanism which restricts microorganisms to areas where they can be tolerated. A breach of this mechanism, allowing them to reach tissues which are normally inaccessible, results in an infechon. Invasion and multiplicahon of the organism in the infected host m result in a pathological condihorr, the clirrical entity of disease. 

When a microorganism breaches the iititial barriers and enters the body tissues, the phagocytes form a formidable defence barrier. Phagocytosis is greatly enhanced by a family of proteins called complement. 

Complement comprises a group of heat-labile serum proteins which, when activated, are associated with the destruction of bacteria in the body in a variety of ways. It is present in low concentrations in serum but, as its action is linked intimately with a second (specific) set of defence mechanisms, its composition and role will be dealt with later in the chapter. 

Pathogenic organisms possess certain properties which enable them to overcome these primary defences. They produce metabolic substances, often enzymic in nature, which facilitate the invasion of the body. The following are examples of these. 

Passively acquired immunity involves no work on the part of the body s defence mechanisms, and produces immediate protection of short duration. 

Human chronic inflammatory diseases are characterized by populations of cells with altered regulation and function. A large body of evidence suggests that many of these cellular abnormalities may be linked to an increase in the production of free radicals and/or deficiencies of antioxidant defence systems. Oxygen free radicals attack cell structures, altering their function, and are cytotoxic. They have therefore been implicated in the pathogenesis of rheumatoid arthritis as well as many other human diseases (HaUiwell, 1991). 

Human skin is the largest organ in the human body. It is fundamentally important to health as the semi-permeable barrier - the first line of defence - between the body and the external world. However, it remains relatively inaccessible to conventional magnetic resonance imaging, firstly because it is thin and therefore requires high spatial resolution, and secondly because it is characterized by relatively short T2 relaxation times, particularly in the outermost stratum comeum. Conventional studies have not usually achieved a resolution better than 70-150 pm, with an echo time of the order of a millisecond or so. As a planar sample, skin has proved amenable to GARField study where it has been possible to use both a shorter echo time and achieve a better spatial resolution, albeit in one direction only. Such studies have attracted the interest of the pharmaceutical and cosmetic industries that are interested in skin hydration and the transport of creams and lotions across the skin. 

The progression of human immunodeficiency virus (HIV) towards its more advanced stages is accompanied by increasing body stores of iron. Iron accumulates in macrophages as well as microglia, endothelial cells and myocytes. The iron burden is especially intense in the bone marrow, brain white matter, muscle and liver. Such excesses of iron will enhance oxidative stress, impair several already compromised immune defence mechanisms and directly promote the growth of microbes (Boelaert et ah, 1996). 

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