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.

Partial Amputation
Partial Amputation

Classification of Disease




The following broad groupings are recognized causes of disease

  • Pathogenic. Pathogenic (disease-producing) organisms cause infectious diseases.
  • Nutritional. Diseases caused by malnutrition (improper or insufficient nutrition) are classified as deficiency diseases. These may be diseases due to a lack of sufficient food or essential elements in the diet, or diseases due to the failure of the body to use the nutrients available in the food.
  • Degenerative. Generally speaking, degeneration (breaking down) of tissues and organs is associated with old age disorders that are a part of the normal wear and tear of the aging process.

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.

  • Anomalies. These are abnormalities in structure and functions of body organs which are present at birth and result in less than perfect normal body functions. Examples of these are
  • Neoplasms. Abnormal growths of cells with no useful purposes are neoplasms (new growths). Cancer and other types of tumors are neoplasms, causing impaired functioning of affected body parts.

Predisposing Causes


These are factors that increase the probability of an individual becoming ill.

  • Age. Age can be both a direct cause of disease, as in the senile degenerative process, or a predisposing factor, as in the childhood diseases.
  • Inadequate self-care. Improper food, poor living conditions, and poor habits of personal hygiene make the body more susceptible to disease.
  • Emotional factors. There is a close relationship between emotional upsets and physical disturbances. True physical illness can develop with emotional factors as a predisposing cause; for example, peptic ulcer or asthma.
  • Sensitivity reactions. Some individuals are hypersensitive (allergic) to certain substances and develop severe reactions if they contact or take these substances into their bodies. Allergic tendencies are considered to have hereditary factors.
  • Classification. Diseases can be classified according to their cause and according to their duration and severity.
  • Acute disease. A disease characterized by a rapid onset and by rapid changes in its progress and symptoms. (An acute disease is not necessarily a serious disease. The common cold, for example, is an acute disease that can be severe, moderate, or mild.)
  • Chronic disease. A continuous or recurrent persistence of a disease.
  • Primary disease. A disease developing independently of any other disease.
  • Secondary disease. A disease that develops as a result of a primary disease or as a result of an injury. In a secondary disease, the body may have much less capacity to deal effectively with additional impaired functions.

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 Type

  • Abrasion. A wound in which outer layers of the skin have been scraped off (fig. 3-1). An abrasion results when a rough object is rubbed forcibly along the skin.
  • Contusion. A subcutaneous or deeper tissue injury, commonly called a bruise, caused by impact with a blunt object. Swelling and black and blue discoloration (ecchymosis) occur as blood leaks internally from injured capillaries. The blood which collects in a pocket of tissues is a hematoma.
  • Strain. A tearing of a muscle or of a tendon attachment of a muscle to a bone due to a sudden and forceful stretching or overexertion in lifting or carrying heavy weights.
  • Sprain. An injury caused by overstretching or tearing ligaments around a joint due to a sudden twisting or stretching of the joint beyond its normal range of motion.
  • Dislocation. This is the displacement of the normal relationship of the bones forming a joint.
  • Fractures. A break in a bone. When there is a communication from the broken bone to the outside surface of the skin through a wound channel or by protrusion of a bone fragment, it is an open fracture. When there is no communication to the overlying skin, it is a closed fracture.
  • Incision. A wound made by a sharpedged instrument such as a knife or razor blade. The wound edges are smooth.
  • Laceration. A wound that is irregular and torn, with jagged edges (fig. 3-1). It is usually caused by objects such as shell fragments, broken glass, or splinters.
  • Penetrating wound. A wound in which a foreign object enters but does not go through the body. There will be a wound of entry but none of exit.
  • Perforating wound. A wound that goes all the way through the body or organ. There will be wounds both of entry and of exit.
  • Puncture. A stab wound, caused by a sharp, pointed object such as a nail, icepick, or needle . The wounding agent may have been withdrawn from the injured area but foreign bodies, including bacteria, that have been carried deep into the tissues may remain.
  • Rupture. A bursting or breakthrough of a muscle or internal organ through its surrounding membrane. A rupture results from the application of internal or external pressure. With a rupture, there may be no injury to the skin or no external evidence of a 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.

  • Bullets. Bullet wounds may be penetrating or perforating. Wounds of entrance and exit may be small unless the bullet hits a bone. Damage to the surrounding tissue will depend on the velocity of the missile.
  • Missile fragments. Sharp, jagged pieces of metal, wood, or glass of almost any size can cause lacerated wounds with much tissue damage. These fragments usually leave no wound of exit (remain embedded in the tissue), so foreign bodies will remain which must be surgically removed.
  • Burn agents. Burn injuries may be caused by thermal (heat) agents such as open flames, steam, or hot gases ; by contact with chemicals such as acids, alkalies, or hydrocarbon fuels (such as gasoline) ; by electricity (lightning or electric current) ; or by radiation from radioactive materials and X-ray machines. The inhalation of flames or hot gases may cause burns of the respiratory tract that require priority treatment because of obstruction to the airway.
  • Blasts. Blasts (explosions) result in sudden, terrific changes in pressure causing rupture of abdominal organs, injury to the lungs resulting in edema and hemorrhage, or injury to the brain (concussion). Frequently, there will be no open wound from this type of agent.
  • Kinetic energy. When a moving vehicle stops suddenly, the passenger continues in motion. Blows received from impact against the vehicle interior cause many serious injuries to internal organs, head, or chest. The sudden stop itself may cause a so-called "whiplash" injury of the cervical vertebrae if the head is suddenly snapped forward and backward. The same kinetic injuries occur when a body is flung against a wall or ground by blast effect.
  • Poison. Puncture wounds into which poison has been introduced are a special complication. Examples are snake and insect bites.
  • Environmental. Extremes of temperature or humidity may cause injury such as heatstroke, frostbite, and immersion foot.

Pathogenic organisms affecting disease and injury




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.

  • Classification.

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.

  • Prevalence.

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.

  • Destruction

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 Pathogenic Organisms

  • Bacteria. Bacteria are minute, one-celled organisms that may occur alone or in large groups called colonies. Each bacterium is independent and may live and reproduce by itself.
  • Viruses. Viruses are protein bodies which are smaller than bacteria. They can multiply only in the presence of living cells. They cause measles, mumps, influenza, and certain other ailments.
  • Rickettsia. Rickettsia are organisms that are larger than viruses but smaller than bacteria. They are carried and spread chiefly by insects such as mites and ticks and cause diseases such as typhus and Rocky Mountain spotted fever.
  • Fungi. Fungi are simple plant organisms which are larger than bacteria. They most often attack the skin, including the hair and nails, causing such chronic infections as ringworm and athlete's foot. Infections caused by fungi are called mycotic infections and can be serious when internal organs are invaded.
  • Worms. A few kinds of worms can live inside the human body and cause disease. The medical term for this general class of worms is helminth. Hookworms and tapeworms are examples of helminths that are common intestinal parasites.
  • Protozoa. Protozoa are one-celled animals, a few of which cause illness in man. Important diseases caused by protozoa include systemic infections such as malaria and amebic dysentery and a local infection such as trichomoniasis which affects the external genitalia.

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 Shape. Significant bacteria can be divided by their shape into three main groups. These groups are the cocci, round or ballshaped bacteria; the bacilli, slender rod-shaped bacteria; and the spirochetes, corkscrew-shaped bacteria.
  • Cocci. The cocci are characterized by formation of pus (pyogenic bacteria). Primary members of this group are staphylococci, streptococci, and diplococci.
  • Staphylococci group themselves in grapelike clusters. They form thick, yellow or white pus. They cause most boils, pyogenic infections of the fingers and hands, and "stitch abscesses" in surgical wounds. they can always be found on the normal skin and almost always in the nasal passages.
  • Streptococci arrange themselves in chains or beadlike formations. They form a thin, watery pus. Streptococci cause a type of infection that tends to spread within body tissues to a greater extent than infections caused by staphylococci. Common in the mouth and throat, they cause systemic disease such as scarlet fever, as well as extremely serious wound infections.
  • Diplococci arrange themselves in pairs. They cause such infections as gonorrhea and meningococci meningitis.
  • Bacilli. Bacilli are characterized by variations in their rod shape from straight to irregular curved and branched shapes. Some bacilli form spores within themselves which may alter their appearance to a bottle or drumstick shape.
  • Escherichia coli belong to a group of true rod-shaped bacilli which normally live in the human intestinal tract. This bacillus is found in the intestinal tract and on the skin of the perineal area. When introduced into wounds, it produces infection characterized by light brown pus with a fecal odor.
  • Clostridium tetani belong to the rodshaped spore formers that appear drumstick shaped while they contain the spores. The spore of Clostridium tetani finds conditions favorable for changing back to its original form when introduced into wounds. Tetanus (lockjafa) is caused either by the introduction of Clostridium tetani or by the introduction of its spores.
  • Corynebacterium diphtheria are usually short, thick rods in palisade (picket fence) arrangement. They cause diphtheria and are spread by nasal or oral droplets from infected persons, as well as by direct contact
  • Spirochetes. The spirochetes are characterized by their corkscrew shape and their ability to move or twist. Treponema pallidum causes syphillis, a communicable disease, usually venereal. The source of infection is contact with lesions of the infected person or, rarely, with moist infected body secretions.

Classification by Oxygen Requirements


Bacteria are divided into two classes, depending on their ability to live in the presence of free oxygen.

  • Aerobic bacteria grow only in the presence of free air or oxygen. Most species of streptococci and staphylococci are aerobic.
  • Anaerobic bacteria cannot live in the presence of free air or oxygen. Clostridium tetani and Clostridium welchii (causing gas gangrene) are anaerobic and are found in street dirt and manured farmland. This is important in the prophylactic and definitive treatment of all traumatic wounds. These organisms may penetrate any deeply contused, lacerated, or punctured wound. If the blood supply and, therefore, the oxygen supply of these tissues is defective, serious infection will occur.
  • Classification by Ability to Cause Disease. Not all bacteria are harmful. Many species of bac-teria in the soil and the air do not ordinarily cause disease in human beings. In addition, there are bacteria which are harmful to animals but not to man. In this manual, organisms that are referred to as nonpathogenic are those which usually do not cause disease in human beings.
  • Classification by Spore Formation. Some bacteria can form spores. In the spore state, the bacteria has produced a wall around its cell which is very resistant to heat and requires prolonged exposure to high temperature and moisture or gas for destruction. The spore forms must be killed in any method used for surgical sterilization, for they can become active bacteria capable of causing severe infections. The most dangerous spore formers are the tetanus bacilli and the bacilli that cause gas gangrene.

Distribution of Bacteria

  • Since bacteria are known to be present in air, water, food; on manmade objects or normally clean skin; and in the mouth, throat, and intestines of healthy human beings, the possible sources of disease and wound infection are almost countless. Pathogenic organisms responsible for diseases other than wound infections are usually inhaled or swallowed. Pathogenic organisms responsible for wound infections are usually introduced through a break in the continuity of the skin.
  • Bacteria flourish in moist surroundings at temperatures near that of the human body. Under less favorable conditions they may continue to exist, without multiplying, for a long time. Usually, all but spore-forming bacteria are eventually destroyed by exposure to sunlight or by drying.

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.

  • The first line of defense, the skin, protects the body's surfaces. It acts like a wall to keep out most bacteria. Bacteria that enter the nose and mouth find another barrier, the mucous membrane that lines the respiratory and digestive systems. Some cells of the membrane secrete mucus which entangles bacteria, while others have cilia which sweep bacteria out of the body.
  • The second line of defense is formed by the white blood cells (wbc) or phagocytes. They engulf and destroy bacteria that pass through the first line of defense. This function of white cells, called phagocytosis, is described in paragraph
  • The third line of defense is immunity. Previous encounters of the body with bacteria will produce a specific resistance or immunity to those particular organisms. This acquired immunity is associated with the formation of antibodies by the body. These antibodies interfere with bacterial invasion in several ways. They may neutralize bacterial toxins, kill the bacteria, make the bacteria more susceptible to attack by white blood cells, or cause the bacteria to clot into little clumps which the white cells can destroy easily.
  • The fourth line of defense is the lymphatic system. Lymph cleans tissues, then flows through vessels into lymph nodes. The nodes act as filters for removal of bacteria.

Body Reactions to disease and injury




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.

  • Causes. Inflammation can be caused by physical, chemical, or bacterial injuring agents.
  • Signs. The signs of inflammation are redness, heat, swelling, pain, and disturbance of function. These five signs are produced by reaction of blood vessels and tissue in the injured area. When injury occurs, the blood vessels dilate, thus increasing the supply of blood to the injured area. The blood is warm and red, producing the first two signs, redness and heat. As the blood vessels dilate, their walls leak and blood serum escapes into the tissues. This results in swelling. Pressure of the swelling on nerve endings causes pain. Disturbance of function can result from the pain orfrom interference by the swelling. While changes in blood vessels are producing the cardinal symptoms of inflammation, the body is reacting to the injury in another way. White cells leave the dilated blood vessels and move through the tissue fluids to the site of injury (fig. 3-4). The cells make a wall around the area to seal off the injurious agent. Within this area the white cells work as scavengers (phagocytes), ingesting small particles of foreign matter, dead tissues, or bacteria if present. As the source of injury is overcome or expelled, tissues return to normal. White cells disperse. Blood vessels return to normal size. Fluids

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 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.

  • Primary Union. A clean incised wound with minimal tissue destruction will heal with very little scar formation. Properly placed sutures (stitches) hold the walls of the wound together, while fiber-forming cells carry repair fibers from one wall to another, binding them together. When the process is completed, the walls are held and healed by a thin scar of fibrous connective tissue. Epithelium grows out from the cut edges of the skin to cover the scar. The hairline appearance of the incision is evidence of healing by primary union .
  • Granulation. When wound edges are left open because of neglect, infection, or excessive loss of tissue, healing takes place by granulation. Granulation tissue is red, soft, and bleeds easily. It is formed of capillaries and fiber cells which gradually cover the walls and base of the wound. Granulation tissue eventually becomes connective tissue and gradually fills the wound. As the skin surface is covered by epithelium, complete healing takes place. A wound that heals by granulation takes a long time and results in a relatively large scar.



&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====

  • In an acute local infection, the five signs of inflammation are usually intensified. In addition, pus usually forms (suppuration). In the process, white cells attempt to wall off and localize the accumulating toxic material. A walled-off accumulation of pus is an abscess, which may occur in any part of the body. The condition that results when pus spreads into subcutaneous tissue surrounding an abscess is cellulitis.
  • A common skin abscess such as a furuncle (boil) is an example of a localized infection caused by staphylococci. The lesion begins as a pustule (a blister containing pus). As the pustule enlarges, the skin becomes reddened, tense, and shiny. Usually the furuncle comes to a head rapidly and ruptures spontaneously, discharging pus. Furuncles may be single or multiple but tend to occur in crops. They may occur anywhere on the skin, particularly on the extremities, buttocks, back of the neck, axillae, and face. Furuncles on or about the nose, upper lip, or beneath the eyes may endanger life by extension along the veins of the face which drain into the venous sinuses of the brain. This is the danger area of the face (fig. 3-7) since a spread of infectious material into the brain can cause encephalitis (inflammation of

brain tissue).

  • Signs and Symptoms of Systemic Infection. As infection spreads beyond a local area, the characteristic signs of systemic infection appear: fever, increased pulse and respiratory rates, headache, malaise (vague general body discomfort), and oftentimes chills. Fever and an increased white blood count (leucocytosis) are considered favorable signs that the internal body defenses are fighting back at the invading organisms. However, general systemic signs are indications that toxemia has caused severe disturbances in many body organs and systems. Infections in an extremity that spread from an initial infected area cause signs indicating involvement of lymph channels and adjacent lymph nodes. Red streaks radiating from an infected area are signs of lymphangitis (inflammation of lymph channels), while swollen, tender glands in the neck, armpit, or groin when the head, arm, or leg, respectively, is involved are signs of lymphadenitis (inflammation of the lymph glands).

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.

  • Rest. Rest allows all the body's defensive effort to be directed toward healing and combating infection. This can hasten the defensive process of walling off an infected area, which will prevent the body from absorbing too much toxin. Rest also reduces movement of an inflamed and painful part.
  • Elevation. Elevation of an inflamed extremity permits the force of gravity to drain swollen tissue spaces and blood vessels. The degree of elevation needed to promote tissue drainage of an extremity is above the heart level. To provide this degree of elevation for the arm, the hand and elbow must be higher than the shoulder; for the leg, the foot and knee must be higher than the hip. A patient for whom rest and elevation of an arm or a leg is ordered must, therefore, usually be confined to bed with the involved extremity elevated along its entire length on properly placed pillow supports.
  • Heat or Cold.
  • Compression. With bandages. Ulcers heal faster when diagnosed as arterial or venous and compression applied.

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.

  • Promotion of Elimination. Toxic materials are eliminated largely by the kidneys. A daily urinary output of at least 1000 ml. is necessary. An increased fluid intake (4000 ml. or more) helps dilute toxins and protect the kidneys. Increased fluid intake also helps bowel elimination.

Aseptic Procedures


Asepsis means freedom from disease-producing microorganisms. The procedures used to accomplish this are classified as medical asepsis and surgical asepsis.

  • Medical asepsis. All of the procedures used that make it possible to care for patients while preventing and controlling the spread of infectious organisms. They include hand washing, disposing of infectious wastes, disinfecting and sanitizing (cleaning) articles after use, and isolating patients with communicable infectious conditions to reduce their contact with other individuals. Medical asepsis reduces the transmission of pathogenic organisms from one person to another.
  • Surgical asepsis. All of the procedures used to sterilize and to keep sterile any object or article that is to be introduced into a wound or that is to penetrate the skin or mucous membrane. Surgical asepsis prevents the introduction of pathogenic organisms into body tissues.