Nursing Study Guide/Causes of disease

Health is a state of physical and mental wellbeing in which the body is able to function fully, with comfort and with the ability to renew and restore itself. On the other hand, disease is any
departure from health; it is any disorder of a body system that interferes with the normal operation of a body process. For the purposes of this manual, disease (or sickness) will be defined as
any departure from health that is caused by pathogenic organisms or any other factor not involving an external physical force; injury (wound) will be defined as any departure from health due
to an external physical force or environmental condition. 
=Classification of Disease=
Causes.
The following broad groupings are recognized causes of disease
However, degeneration may occur at any age as a result of chronic infection or repeated injury which leads to a loss of vitality or function. Arthritis, for example, may result from aging, injuries, or infections.
Predisposing Causes.
These are factors that increase the probability of an individual becoming ill.
Classification of Injuries.
Injuries and wounds are classified by type, location, and causative agent. The extent of injury is described as severe, moderate, slight, superficial (involving surface tissue only), or deep (involving tissues below the subcutaneous layer). When there is no break in the continuity of the skin or mucous membrane, the injury is referred to as a closed wound. When the skin or mucous membrane is cut or penetrated, the injury is referred to as an open wound.
Classification by Location.
Wounds are classified according to anatomical parts of the body as head wounds (these are subdivided into skull, face, and jaw wounds); chest wounds; abdominal wounds; wounds of the extremities (arms or legs); wounds of joints; and spinal and pelvic wounds. The part of the body most severely injured determines the primary classification of multiple wounds.
Classification by Causative Agent.
The agent responsible is especially important in diagnosis and treatment because of some known factors in the type of tissue damage that results from different causative agents.
=Pathogenic organisms affecting disease and injury=
Microorganisms.
All things that exist in nature are classified into three general groups—animal, vegetable, and mineral. The animal and vegetable groups are living and are therefore classed as organisms (any living thing). Living plants and animals too small to be seen singly except with the aid of a microscope are microorganisms. Varying in size, shape, and their effect on man, they become visible to the naked eye only when they form colonies or groups.
Microorganisms belonging to the animal kingdom are called protozoa ; those belonging to the vegetable group are the bacteria, fungi (yeasts and molds), the rickettsia, the spirochetes, and the viruses. Protozoa cause such diseases as malaria and amoebic dysentery. Most infectious diseases of man are caused by bacteria or viruses.
Microorganisms are found almost everywhere ; in the air, on uniforms, on the hands, on the furniture, on the feet, on flies and other insects, and on the floor. They are even taken into the body with every breath and with every mouthful of food. Fortunately, many of these are nonpathogenic (not harmful) to man. Moreover, natural body defenses protect to a certain extent against the harmful ones. As microorganisms are constantly present even in the air itself, complete absence of microorganisms on items commonly used is impossible. The goal is to have as few microorganisms present as possible by using all known preventive measures against infection and disease.
There are many methods of destroying microorganisms, but some are more effective than others. Washing with soap and water or exposure to light, fresh air, heat, and chemicals are effective only with some microorganisms, not all. The only known methods that assure complete destruction of microorganisms are steam under pressure (autoclaving, the procedure used by most hospitals), burning (flaming or actual burning), and exposure to a gas such as ethylene oxide. These three methods destroy even resistant spores (microorganisms encased in a hard outer shell) and leave an article sterile (absolutely free of all microorganisms).
Classification of Bacteria.
The identification of bacteria under the microscope helps to confirm the diagnosis of many infectious diseases. Bacteria can be classified and described in terms of shape, oxygen requirements, ability to cause disease, and ability to form spores.
Classification by Oxygen Requirements.
Bacteria are divided into two classes, depending on their ability to live in the presence of free oxygen.
The Body's Defenses Against Pathogenic Organisms.
The body has four lines of defense to combat bacteria. In the healthy body, these defenses show a remarkable ability to fight off bacteria and to withstand their effects. However, such factors as injury, exposure, fatigue, and malnutrition lower the body's defenses. 
=Body Reactions to disease and injury=
Inflammation.
Inflammation is the local reaction of the body to irritation or injury. It occurs in tissue that is injured but not destroyed. It is a defensive and protective effort by the body to isolate and eliminate the injuring agent and to repair the injury. A certain degree of inflammation takes place following any type of injury, including a wound made under aseptic conditions by a surgeon. 
flow away through the lymphatics. If tissue has been destroyed, it is replaced by scar tissue. Thus, the dilation of blood vessels and the mobilization of white cells against the injuring agent are the two basic reactions in the inflammatory process.
Healing.
Healing is a process related to inflammation, for both are started by tissue injury. It would be ideal if the body could heal itself by replacing all damaged tissues with an exact counterpart; then, an eye would be replaced with a new eye and a tooth with a new tooth. But very few tissues are replaced in kind. Examples of tissues which may replace themselves are liver tissue, kidney tubules, and connective tissue. Bone — which is one kind of connective tissue — may replace itself if broken; that is, the broken bone is repaired by the formation of new bony tissue. Healing in most tissues is, however, a process of replacement ; the destroyed tissue is replaced by scar tissue (fibrous type of connective tissue). If brain cells are destroyed, they are replaced by connective tissue. If the heart muscle is injured, the damaged fibers are replaced by connective tissue. When a tooth is pulled or an eye is lost, the sockets are filled with connective tissue. Hence, replacement by scar tissue is the usual order in healing. The healing process tak6s place in one of two ways — by primary union or by granulation. 
Infections.
&amp;General. Infection is the entry and development or multiplication of an infectious agent in the body. The agent can be any pathogenic organism. Factors that contribute to the ability of the infectious agent to produce infectious disease include the number and kind of invading organisms, the ability of the body to resist infection, and the virulence of the infecting organisms. Virulence is the ability of pathogenic organisms to overcome, at least temporarily, the defensive reactions of the body (phagocytosis, immunity, and lymphatic involvement) which are all mobilized when infection occurs. Virulent organisms have the ability to multiply rapidly within body tissues and to form toxins (poisonous waste products). Pathogenic organisms produce different kinds of toxins; some toxins destroy tissue cells, some dissolve blood cells (hemolysis), and some are absorbed rapidly into the blood to cause toxemia, a generalized systemic reaction to infection.
Acute Local Injection.
brain tissue).
General Therapeutic Measures in Acute Inflammation and Infections.
The general therapeutic measures used in treating acute inflammation and infection are based on the need to (1) assist the body to mobilize its natural internal defenses, (2) relieve pain, (3) promote healing, (4) prevent complications, and (5) control the spread of infectious organisms when present. The general measures used are rest, elevation of an involved extremity, use of heat or cold, drug therapy, promotion of elimination of waste products, and aseptic procedures to prevent and control the spread of infection. 
Effect of heat. Heat applied to the body dilates the capillaries and increases blood flow. The improved blood supply increases the number of white cells in the area to combat pathogenic organisms and aid the formation and localization of pus. Heat is never applied, however, in undiagnosed abdominal inflammatory conditions—if the inflammation is due to an inflamed appendix, the application of heat could contribute to a ruptured appendix and peritonitis.
Effect of cold. Cold causes the blood vessels to constrict and also tends to reduce edema. It reduces the pain of inflammation because it reduces the sensitivity of nerve endings in the skin. When applied immediately after an injury, it prevents or relieves swelling.
Drug Therapy. The type of drug to be used in combating inflammation and infection is determined by the medical officer when the infecting organism is identified. Cultures, smears, or the development of particular signs or symptoms help in this identification. In addition to anti-infective or anti-inflammatory drugs, analgesic drugs to relieve pain and to insure rest are often indicated. 
Aseptic Procedures.
Asepsis means freedom from disease-producing microorganisms. The procedures used to accomplish this are classified as medical asepsis and surgical asepsis.