Disease

Disease, any harmful deviation from an organism 's normal structural or functional state, generally associated with certain signs and symptoms and of a nature different from physical injury. A diseased organism also displays signs or indications that suggest its unhealthy condition. Thus, to recognize the hallmarks of disease, the normal condition of an organism has to be understood. The disease research is called pathology. It includes the identification of the disease's origin (etiology), knowing the physiological processes (pathogenesis), the anatomical modifications associated with the disease cycle (morphological changes), and the practical effects of those changes. The proper diagnosis of the source of a disease is important. Human beings, other animals and plants are all vulnerable to some type of disease. However, that which interferes with the normal functioning of one type of organism may not affect the other types. The natural state of an organism is a status of fragile physiological equilibrium or homeostasis in biological , physical and functional systems, sustained by a variety of mechanisms. In some cases the affected mechanisms are clearly indicated, but in most cases a complex of mechanisms is disturbed, initially or sequentially, and it is elusive to define accurately the pathogenesis of the ensuing disease. For example, death in humans and other mammals often results directly from heart failure or lung failure, but the preceding sequence of events can be highly complex , involving distinctions.