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Inflammation, Tissue Repair, and Fever

By Frances Campbell,2014-04-16 21:58
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Inflammation, Tissue Repair, and Fever

    Inflammation, Tissue Repair, and Fever

    The Inflammatory Response

    ; Inflammation is the reaction of vascularized tissue to local injury. The causes of inflammation are

    many & varied. Inflammation commonly results because of an immune response to infectious

    microorganisms.

    ; Other causes of inflammation are trauma, surgery, caustic chemicals, extremes of heat and cold,

    and ischemic damage to body tissues. Inflammatory conditions are named by adding the suffix-itis

    to the affected organ or system.

    Acute inflammation is the early (almost immediate) response to injury. It is nonspecific and may be evoked by any injury short of one that is immediately fatal.

    Cardinal Signs

    ; These signs are rubor (redness), tumor (swelling), calor (heat), and dolor (pain). These signs and

    symptoms, which are apparent when inflammation occurs on the surface of body, may not be

    present when internal organs are involved.

    ; In addition to the cardinal signs that appear at the site of injury, systemic manifestations (e.g.,

    fever) may occur as chemical mediators produced at the site of inflammation gain entrance to the

    circulatory system.

    The Vascular Response

    ; The vascular, or hemodynamic, changes that occur with inflammation begin almost immediately

    after injury and are initiated by a momentary constriction of small blood vessels in the area.

    ; This vasoconstriction is followed rapidly by vasodilation of the arterioles and venules that supply

    the area. As a result, the area becomes congested, causing the redness (erythema) and warmth

    associated with acute inflammation.

    ; Accompanying this hyperemic vascular response is an increase in capillary permeability, which

    causes fluid to move into the tissues and cause swelling, pain, and impaired function.

    ; The exudation or movement of the fluid out of the capillaries and into the tissue spaces dilutes the

    offending agent.

    The Cellular Stage

    The cellular stage of acute inflammation is marked by movement of phagocytic white blood cells (leukocytes) into the area of injury. Two types of leukocytes participate in the acute inflammatory responsethe granulocytes and monocytes.

    Granulocytes

    ; Granulocytes are identifiable because of their characteristic cytoplasmic granules. These white

    blood cells have distinctive multilobed nuclei. The granulocytes are divided into three types (i.e.,

    neutrophils, eosinophils, and basophils) according to the staining properties of the granules.

    ; The neutrophil is the primary phagocyte that arrives early at the site of inflammation, usually

    within 90 minutes of injury.

    ; The neutrophils’ cytoplasmic granules contain enzymes and other antibacterial substances that are

    used in destroying and degrading the engulfed particles.

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    ; The cytoplasmic granules of the eosinophils stain red with the acid dye eosin. These granulocytes

    increase in the blood during allergic reactions and parasitic infections.

    ; The granules of the basophils stain blue with a basic dye. The granules of these granulocytes

    contain histamine and other bioactive mediators of inflammation.

    The Inflammatory Response

     Inflammation represents the response of body tissue to immune reactions, injury, or ischemic damage. The classic response to inflammation includes redness, swelling, heat, pain or discomfort, & loss of

    function.

     The manifestations of an acute inflammatory response can be attributed to the immediate vascular changes that occur (vasodilation and increased capillary permeability), the influx of inflammatory cells such as neutrophils, and, in some cases, the widespread effects of inflammatory mediators, which produce fever and other systemic signs and symptoms.

     The manifestations of chronic inflammation are due to infiltration with macrophages, lymphocytes, and fibroblasts, leading to persistent inflammation, fibroblast proliferation, and scar formation. Mononuclear Phagocytes

    ; The monocytes are the largest of the white blood cells and constitute 3% to 8% of the total blood

    leukocytes. The circulating life span of the monocyte is three to four times longer than that of the

    granulocytes, and these cells survive for a longer time in the tissues.

    ; The monocytes, which migrate in increased numbers into the tissues in response to inflammatory

    stimuli, mature into macrophages. Within 24 hours, mononuclear cells arrive at the inflammatory

    site, and by 48 hours, monocytes and macrophages are the predominant cell types. Cellular Response

    ; The sequence of events in the cellular response to inflammation includes: (1) pavementing, (2)

    emigration, (3) chemotaxis, and (4) phagocytosis.

    ; During the early stages of the inflammatory response, fluid leaves the capillaries, causing blood

    viscosity to increase. The release of chemical mediators (i.e., histamine, leukotrienes, and kinins)

    ; Emigration is a mechanism by which the leukocytes extend pseudopodia, pass through the

    capillary walls by ameboid movement, and migrate into the tissue spaces.The process by which

    leukocytes migrate in response to a chemical signal is called chemotaxis.

    ; During the next and final stage of the cellular response, the neutrophils and macrophages engulf

    and degrade the bacteria and cellular debris in a process called phagocytosis.

    Chronic Inflammation

    ; Characteristic of chronic inflammation is an infiltration by mononuclear cells (macrophages) and

    lymphocytes, instead of the influx of neutrophils commonly seen in acute inflammation. Chronic

    inflammation also involves the proliferation of fibroblasts instead of exudates. Local Manifestations of Inflammation

    ; Inflammatory exudates often are composed of a combination of these types. Serous exudates are

    watery fluids low in protein content that result from plasma entering the inflammatory site.

    Hemorrhagic exudates occur when there is severe tissue injury that causes damage to blood

    vessels or when there is significant leakage of red cells from the capillaries.

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    ; Fibrinous exudates contain large amounts of fibrinogen and form a thick and sticky meshwork,

    much like the fibers of a blood clot. Membranous or pseudomembranous exudates develop on

    mucous membrane surfaces & are composed of necrotic cells enmeshed in a fibropurulent exudate.

    Systemic Manifestations of Inflammation

    White Blood Cell Response (Leukocytosis and Leukopenia)

    ; The white blood cell count usually increases to 15,000 to 20,000 cells/µL (normal 4000 to 10,000

    cells/µL). After being released from the bone marrow, circulating neutrophils have a life span of

    only about 10 hours and therefore must be constantly replaced if their numbers are to be adequate. ; Bacterial infections produce a relatively selective increase in neutrophils (neutrophilia), whereas

    parasitic and allergic responses induce eosinophilia.

    ; Viral infections tend to produce neutropenia (decreased numbers of neutrophils) and

    lymphocytosis. Leukopenia is also encountered in infections that overwhelm persons with other

    debilitating diseases such as cancer.

    Lymphadenitis

    ; Localized acute and chronic inflammation may lead to a reaction in the lymph nodes that drain the

    affected area. Painful palpable nodes are more commonly associated with inflammatory processes,

    whereas non-painful lymph nodes are more characteristic of neoplasms.

    ; The systemic manifestations of inflammation include an increased ESR, fever, and leukocytosis

    (or in some cases, leukopenia). These responses are mediated by release of the cytokines. ; Localized acute and chronic inflammation may lead to a reaction in the lymph nodes and

    enlargement of the lymph nodes that drain the affected area.

    Tissue Repair & Wound Healing

     Body organs and structures contain two types of tissues: parenchymal and stromal. The

    parenchymal tissues contain the functioning cells of an organ or body part (e.g., hepatocytes, renal

    tubular cells).

     The stromal tissues consist of the supporting connective tissues, blood vessels, and nerve fibers.

     Injured tissues are repaired by regeneration of parenchymal cells or by connective tissue repair in

    which scar tissue is substituted for the parenchymal cells of the injured tissue.

     The primary objective of the healing process is to fill the gap created by tissue destruction and to

    restore the structural continuity of the injured part.

    Regeneration

     Regeneration involves replacement of the injured tissue with cells of the same parenchymal type,

    leaving little or no evidence of the previous injury. The ability to regenerate varies with the tissue

    and cell type. Body cells are divided into three types according to their ability to undergo

    regeneration: labile, stable, or permanent cells.

     Labile cells are those that continue to divide and replicate throughout life, replacing cells that are

    continually being destroyed.

     Labile cells can be found in tissues that have a daily turnover of cells.

     Stable cells are those that normally stop dividing when growth ceases. However, these cells are

    capable of undergoing regeneration when confronted with an appropriate stimulus.

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     Permanent or fixed cells cannot undergo mitotic division. The fixed cells include nerve cells,

    skeletal muscle cells, and cardiac muscle cells. These cells cannot regenerate; once destroyed, they

    are replaced with fibrous scar tissue that lacks the functional characteristics of the destroyed tissue. Connective Tissue Repair

     Connective tissue replacement is an important process in the repair of tissue. It allows replacement

    of nonregenerated parenchymal cells by a connective tissue scar. Depending on the extent of tissue

    loss, wound closure and healing occur by primary or secondary intention. A sutured surgical

    incision is an example of healing by primary intention. Larger wounds (e.g., burns and large

    surface wounds) that have a greater loss of tissue and contamination, heal by secondary intention.

     Wound healing is commonly divided into three phases: the inflammatory phase, the proliferative

    phase, and the maturational or remodeling phase

    Inflammatory Phase

    The inflammatory phase of wound healing begins at the time of injury and is a critical period because it prepares the wound environment for healing. It includes hemostasis and the vascular and cellular phases of inflammation.

    Proliferative Phase

    The proliferative phase of healing usually begins within 2 to 3 days of injury and may last as long as 3 weeks in wounds healing by primary intention. The primary processes during this time focus on the building of new tissue to fill the wound space. The key cell during this phase is the fibroblast. The

    fibroblast is a connective tissue cell that synthesizes and secretes collagen and other intercellular elements needed for wound healing.

    Remodeling Phase

    The third or remodeling phase of wound healing begins approximately 3 weeks after injury and can continue for 6 months or longer, depending on the extent of the wound. As the term implies, there is continued remodeling of scar tissue by simultaneous synthesis of collagen by fibroblasts and lysis by collagenase enzymes.

    Factors That Affect Wound Healing

    1. Malnutrition

    ; Successful wound healing depends in part on adequate stores of proteins, carbohydrates, fats,

    vitamins, and minerals. It is well recognized that malnutrition slows the healing process, causing

    wounds to heal inadequately or incompletely.

    ; Carbohydrates are needed as an energy source for white blood cells. Carbohydrates also have a

    protein-sparing effect and help to prevent the use of amino acids for fuel when they are needed

    for the healing process.

    ; Although most vitamins are essential cofactors for the daily functions of the body, only vitamins

    A and C have been shown to play an essential role in the healing process. Vitamin C is needed

    for collagen synthesis.

    ; Vitamin A functions in stimulating and supporting epithelialization, capillary formation, and

    collagen synthesis.

2. Blood Flow and Oxygen Delivery

    ; For healing to occur, wounds must have adequate blood flow to supply the necessary

    nutrients and to remove the resulting waste, local toxins, bacteria, and other debris.

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    ; Impaired wound healing caused by poor blood flow may occur as a result of wound

    conditions (e.g., swelling) or pre-existing health problems. Arterial disease and venous

    pathology are well-documented causes of impaired wound healing. In situations of trauma,

    a decrease in blood volume may cause a reduction in blood flow to injured tissues. 3. Impaired Inflammatory and Immune Responses

    ; Inflammatory and immune mechanisms function in wound healing. Inflammation is

    essential to the first phase of wound healing, and immune mechanisms prevent infections

    that impair wound healing.

    ; Among the conditions that impair inflammation and immune function are disorders of

    phagocytic function, diabetes mellitus, and therapeutic administration of corticosteroid

    drugs.

    ; The therapeutic administration of corticosteroid drugs decreases the inflammatory process

    and may delay the healing process. These hormones decrease capillary permeability during

    the early stages of inflammation, impair the phagocytic property of the leukocytes, and

    inhibit fibroblast proliferation and function.

    4. Infection, Wound Separation, and Foreign Bodies

    ; Wound contamination, wound separation, and foreign bodies delay wound healing.

    Infection impairs all dimensions of wound healing.

    ; It prolongs the inflammatory phase, impairs the formation of granulation tissue, and

    inhibits proliferation of fibroblasts and deposition of collagen fibers. Body Temperature Regulation

    ; The temperature within the deep tissues of the body (core temperature) is normally maintained

    within a range of 36.0?C to 37.5?C

    ; Body temperature reflects the difference between heat production and heat loss. Body heat is

    generated in the tissues of the body, transferred to the skin surface by the blood, and then released

    into the environment surrounding the body dissipation.

    ; The thermostatic set point of the thermoregulatory center is set so that the core temperature is

    regulated within the normal range. When body temperature begins to rise above the normal range,

    heat-dissipating behaviors are initiated; when the temperature falls below the normal range, heat

    production is increased.

    ; Metabolism is the body’s main source of heat production. The sympathetic neurotransmitters,

    epinephrine and norepinephrine, which are released when an increase in body temperature is

    needed, act at the cellular level to shift metabolism so energy production is reduced and heat

    production is increased.

    ; Shivering is initiated by impulses from the hypothalamus. The first muscle change that occurs with

    shivering is a general increase in muscle tone, followed by an oscillating rhythmic tremor

    involving the spinal-level reflex that controls muscle tone.

    Mechanisms of Heat Loss

    a. Radiation. Radiation involves the transfer of heat through the air or a vacuum. Heat from the sun is

    carried by radiation. The human body radiates heat in all directions. The ability to dissipate body

    heat by radiation depends on the temperature of the environment. Environmental temperature must

    be less than that of the body for heat loss to occur.

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    b. Conduction. Conduction involves the direct transfer of heat from one molecule to another. Blood

    carries, or conducts, heat from the inner core of the body to the skin surface. Normally, only a small

    amount of body heat is lost through conduction to a cooler surface. However, loss of heat by

    conduction to air represents a sizable proportion of the body’s heat loss.

    c. Convection. Convection refers to heat transfer through the circulation of air currents. Normally, a

    layer of warm air tends to remain near the body’s surface; convection causes continual removal of

    the warm layer and replacement with air from the surrounding environment.

    d. Evaporation. Evaporation involves the use of body heat to convert water on the skin to water vapor.

    Water that diffuses through the skin independent of sweating is called insensible perspiration.

    Fever

    ; Fever, or pyrexia, describes an elevation in body temperature that is caused by a cytokine-induced

    upward displacement of the set point of the hypothalamic thermoregulatory center. ; Fever can be caused by a number of microorganisms and substances that are collectively called

    pyrogens .

    ; Many proteins, breakdown products of proteins, and certain other substances, including

    lipopolysaccharide toxins released from bacterial cell membranes, can cause the set point of the

    hypothalamic thermostat to increase.

    Patterns

    ; The patterns of temperature change in persons with fever vary and may provide information about

    the nature of the causative agent. These patterns can be described as intermittent, remittent, sustained,

    or relapsing.

    ; An intermittent fever is one in which temperature returns to normal at least once every 24 hours.

    Intermittent fevers are commonly associated with conditions such as gram-negative/positive sepsis,

    abscesses, and acute bacterial endocarditis.

    ; In a remittent fever, the temperature does not return to normal and varies a few degrees in either

    direction. It is associated with viral upper respiratory tract infections.

    ; In a sustained or continuous fever, the temperature remains above normal with minimal variations

    (usually less than 0.55?C or 1?F). Sustained fevers are seen in persons with drug fever. ; A recurrent or relapsing fever is one in which there is one or more episodes of fever, each as long

    as several days, with one or more days of normal temperature between episodes. Relapsing fevers

    may be caused by a variety of infectious diseases, including tuberculosis,

    Manifestations

     The physiologic behaviors that occur during the development of fever can be divided into four

    successive stages: a prodrome; a chill, during which the temperature rises; a flush; & defervescence.

     During the first or prodromal period, there are nonspecific complaints, such as mild headache and

    fatigue, general malaise, and fleeting aches and pains.

     During the second stage or chill, there is the uncomfortable sensation of being chilled and the onset

    of generalized shaking, although the temperature is rising.

     The third stage or flush begins, during which cutaneous vasodilation occurs and the skin becomes

    warm and flushed. The fourth, or defervescence, stage of the febrile response is marked by the

    initiation of sweating.

     Common manifestations of fever are anorexia, myalgia, arthralgia, and fatigue. These discomforts

    are worse when the temperature rises rapidly or exceeds 39.5?C. Respiration is increased, and the

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    heart rate usually is elevated. Dehydration occurs because of sweating and the increased vapor losses

    caused by the rapid respiratory rate.

Diagnosis and Treatment

    Sometimes it is difficult to establish the cause of a fever. A prolonged fever for which the cause is difficult to ascertain is often referred to as fever of unknown origin (FUO). FUO is defined as a temperature

    elevation of 38.3?C or higher that is present for 3 weeks or longer. Among the causes of FUO are malignancies (i.e., lymphomas, metastases to the liver and central nervous system); infections such as human immunodeficiency virus or tuberculosis,

    The methods of fever treatment focus on modifications of the external environment intended to increase heat transfer from the internal to the external environment,

    a. Modification of the environment ensures that the environmental temperature facilitates heat transfer

    away from the body. Sponge baths with cool water or an alcohol solution can be used to increase

    evaporative heat losses.

    b. Care must be taken so that cooling methods do not produce vasoconstriction and shivering that

    decrease heat loss and increase heat production.

    c. Adequate fluids and sufficient amounts of simple carbohydrates are needed to support the

    hypermetabolic state and prevent the tissue breakdown that is characteristic of fever. d. Antipyretic drugs, such as aspirin and acetaminophen, often are used to alleviate the discomforts of

    fever and protect vulnerable organs, such as the brain, from extreme elevations in body temperature.

    These drugs act by resetting the hypothalamic temperature control center to a lower level, presumably by blocking the activity of cyclooxygenase, an enzyme that is required for the conversion of arachidonic acid to prostaglandin E2

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