ABSTRACT
This chapter overviews the nature and appearances of the major disease processes, followed by some insight into the underlying mechanisms involved. The effectiveness of the skin in excluding pathogenic micro-organisms is demonstrated by the rapidity with which bacteria can enter the body through breaches in the skin, whether these be traumatic or surgical. As well as providing a physical barrier, sweat glands and sebaceous glands secrete lactic acid and fatty acids with bacteriocidal properties. The involvement of cellular and humoral factors in the defence against infection was appreciated by the end of the nineteenth century. The cell type that plays the most critical role in acute inflammation is the neutrophil, whereas lymphocytes and cells of the mononuclear/macrophage lineage are the main participants in chronic inflammation. Cellular and humoral factors operate in both natural and specific immunity. Neutrophils, eosinophils and macrophages are the cellular defences contributing to natural immunity and are supported by humoral factors in the form of complement.
