Chapter 09-Inflammation, Tissue Repair, and Wound Healing

Objectives

• Describe the vascular changes in an acute inflammatory response.
• Characterize the interaction of adhesion molecules, chemokines, and cytokines in leukocyte adhesion, migration, and phagocytosis.
• List four types of inflammatory mediators and state their function.
• Describe the differences in acute and chronic inflammation.
• Compare labile, stable, and permanent cell types in terms of their capacity for regeneration.
• Trace the wound-healing process through the inflammatory, proliferative, and remodeling phases.
• Explain the effects of malnutrition, ischemia and oxygen deprivation, impaired immune and inflammatory responses, corticosteroids, diabetes mellitus, infection, wound separation, and foreign bodies on wound healing.

Case Study: Carlton's Injury

• Carlton, a 6-year-old boy, cut his foot on a shell at the beach.
• The wound became red, painful, warm, and swollen a day later.

Inflammation

• A response intended to eliminate the cause of cellular injury and generate new tissue.
• How:
  • Neutralize toxins, foreign agents, or infectious agents.
  • Initiate the repair process.

Causes of Inflammation

• Immune response to infectious microorganisms
• Trauma
• Surgery
• Caustic chemicals
• Extremes of heat and cold
• Ischemic damage to body tissues
• Radiation
• Sun exposure
• Radiation therapy

Basic Patterns of Inflammation

• Acute inflammation
  • Of relatively short duration; nonspecific early response to injury
  • Aimed primarily at removing the injurious agent and limiting tissue damage
  • Infiltration of neutrophils
  • Exudate producing
• Chronic inflammation
  • Longer duration lasting for days to years
  • A recurrent or progressive acute inflammatory process or a low-grade smoldering response that fails to evoke an acute response
  • Infiltration by mononuclear cells (macrophages) and lymphocytes
  • Proliferation of fibroblasts

Acute Inflammation: Cells

• Cells of Inflammation
  • Leukocytes—monocytes, neutrophils, eosinophils, basophils, mast cells, and macrophages
    • adhesion
    • margination
    • transmigration
    • chemotaxis
  • Connective tissue cells
    • fibroblasts
    • macrophages
    • mast cells
  • Endothelial cells
    • Lining cells of the blood vessels
    • Produce agents to prevent blood clotting
    • Significant importance in the inflammatory response

Acute Inflammation: Vessels

• Vascular phase: cardinal signs of inflammation
  • Changes in blood vessels
    • Vasodilation: causes redness (rubor) and heat (calor)
    • Increase in vascular permeability: causes swelling (tumor), which then results in loss of function (functio laesa)
    • Stagnation of blood flow occurs: clotting aids in localization of infectious organisms

Vascular Changes that May Occur with Inflammation

• Immediate transient response
  • Usually occurs with minor injuries
  • Rapid onset, reversible, short duration (15-30 minutes)
• Immediate sustained response
  • Usually occurs with more serious injuries
  • May last several days
  • Results from vascular injury
• Delayed hemodynamic response
  • Usually occurs 4-24 hours after exposure to radiation
    • Sunburn
    • Radiation therapy

Acute Inflammation: Cells Doing Things

• Acute inflammation is marked by changes in the endothelium lining the vessels and movement of phagocytic white cells (leukocytes, primarily NEUTROPHILS) into the area of injury or infection.
• Two types of leukocytes participate in the acute inflammatory response:
  • Granulocytes (neutrophils, eosinophils, and basophils)
  • Monocytes (the largest of the white blood cells)

Acute Inflammation: Cell Activities

• Margination and adhesion to the endothelium
  • Leukocytes slow down and “roll” along the vessel wall.
  • Interaction between leukocytes and vascular endothelium starts the inflammatory response.
  • Leukocyte accumulation: margination, caused by cytokines such as selectins and integrins.
  • Endothelial cells separate slightly, allowing transmigration
• Transmigration across the endothelium
  • Leukocytes change shape, extend pseudopods, and squeeze through the vessel wall due to chemotactic factors; cells migrate into the tissue spaces.

Margination Process

• Rolling (Selectins)
• Firm adhesion (B1, B2 integrins)
• Transmigration (PCAM-1, etc.)
• Chemotaxis

Acute Inflammation: Cell Activities (Continued)

• Chemotaxis
  • Chemoattractants from bacteria, chemokines, cellular debris, and protein direct leukocyte movement.
  • Chemokines are very important during the early phases of inflammation
  • Secreted by immune cells (macrophages) and non-immune cells
• Leukocyte Activation
  • Monocytes, neutrophils, and tissue macrophages are activated to engulf and degrade bacteria and cellular debris → PHAGOCYTOSIS (phage-to eat; cyto-cell)

Acute Inflammation: Phagocytosis

• RECOGNITION AND ADHERENCE
  • Particles bind to the receptors on the surface of phagocytic cells
• ENGULFMENT
  • Trapping the agent causes the surrounding (engulfment) of a cell and activates the “killing” potential of the cell—this is called OPSONIZATION
• INTRACELLULAR KILLING
  • Toxic oxygen and nitrogen products
  • Lysosomes
  • Proteases

Classification of Inflammatory Mediators by Function

• Vasoactive and smooth muscle–constricting properties
• Chemotactic factors such as complement fragments and cytokines
• Plasma proteases activate complement and components of the clotting system
• Reactive molecules and cytokines liberated from leukocytes when released into the extracellular environment can damage the surrounding tissue which causes more local damage

Systemic Manifestations of Inflammation

• Acute-phase response
  • Changes in plasma protein concentrations, skeletal muscle catabolism
  • Alterations in white blood cell count (leukocytosis or leukopenia)
    • Bacteria generally increase neutrophils
    • Parasites and allergic responses generally increase basophils
  • Increased erythrocyte sedimentation rate
  • A decrease in WBC’s may be seen in overwhelming infection
  • Fever—most obvious sign of inflammation
• Sepsis and systemic inflammatory response syndrome also called “septic shock” (severe)
• Lymphadenitis: non-specific sign
  • Enlarged, tender, palpable lymph nodes

Acute Inflammation: Inflammatory Mediators

• Histamines
  • From mast cells
  • Dilation of arterioles and increases the permeability of venules
• Arachidonic Acid Metabolites
  • From cell membranes
  • Prostaglandins: causes vasodilation and bronchoconstriction; potentiates histamine; associated with anaphylaxis
  • Thromboxane: causes vasoconstriction and bronchoconstriction; promotes platelet function
• Platelet-activation Factor
  • Activates neutrophils and attracts eosinophils
  • Causes platelet activation

Acute Inflammation: Inflammatory Mediators (Continued)

• Plasma proteins
  • Promotes blood clotting
  • Activates the complement system
  • Activated proteins become proteolytic enzymes which can affect immunity and inflammation
• Vasoactive peptides
  • Bradykinin: increases vascular permeability, dilation of blood vessels, and contraction of smooth muscle; short duration of action
• Cytokines and Chemokines
  • These modulate the actions of other cells that are important in the immune response
• Nitric oxide and Oxygen-derived free radicals
  • Multiple roles in inflammation
  • Platelet aggregation
  • Causes increased tissue injury

Acute Inflammation: Production Sites

• Liver produces plasma-derived mediators like acute-phase proteins and complement proteins
• Cells produce cell-derived mediators
  • Mast cells: Histamine, Serotonin
  • Platelets: Lysosomal enzymes
  • Neutrophils, Leukocytes, Macrophages: Prostaglandins, Leukotrienes, Platelet-activating factor, Cytokines, Oxygen-derived free radicals

Summary: Acute Inflammation: Inflammatory Mediators

• Note particularly the acute-phase response of the cellular response.

Acute Inflammation: Exudates

• Serous Exudates
  • Watery fluids low in protein content
  • 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
• Membranous or Pseudomembranous Exudates
  • Develop on mucous membrane surfaces
  • Composed of necrotic cells enmeshed in a fibropurulent exudate
• Purulent or Suppurative Exudates
  • Contain pus; composed of degraded white blood cells, proteins, and tissue debris
• Fibrinous Exudates
  • Contain large amounts of fibrinogen and form a thick and sticky meshwork

Abscess Formation

• Bacterial invasion and development of inflammation
• Continued bacterial growth, neutrophil migration, liquefaction tissue necrosis, and development of a purulent exudate
• Walling off the inflamed area and its purulent exudate to form an abscess

Chronic Inflammation

• Chronic inflammation
  • Non-specific
  • Granulomatous inflammation
• Characteristics
  • self-perpetuating
  • may last weeks, months, or years
  • Infiltration by mononuclear cells (macrophages) and lymphocytes
  • Proliferation of fibroblasts

Chronic Inflammation: Nonspecific

• Accumulation of macrophages and lymphocytes at the site of injury
• Chemotaxis results in macrophage infiltration and accumulation in inflamed site
• Fibroblast proliferation and scar formation

Chronic Inflammation: Granulomatous

• Associated with foreign bodies such as
  • Splinters
  • Sutures
  • Silica, asbestos
• Associated with microorganisms that cause
  • Tuberculosis
  • Syphilis, sarcoidosis
  • Deep fungal infections
  • Brucellosis

Question 1: Carlton's Wound

• What is the physiologic mechanism causing the Carlton’s wound to become red, hot, swollen, and painful?
• How is this different than the inflammatory response that might occur in an internal organ?

Question

• Which molecules will induce endothelial cell retraction?
  • C. Histamine
• Rationale: Histamine is the primary activator of endothelial retraction and increased permeability of the vessels.

Question 2: Carlton's Inflammatory Response

• What are the immunologic events that are happening at the local level during Carlton’s acute inflammatory response?

Types of Structures of Body Organs and Tissues

• 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, extracellular matrix, and nerve fibers

Types of Body Cells

• Labile Cells
  • Continue to divide and replicate throughout life, replacing cells that are continually being destroyed
  • Examples: surface skin cells, oral cavity, vagina, cervix; lining cells of the GI tract, uterus, urinary tract; bone marrow
• Stable Cells
  • Normally stop dividing when growth ceases
  • Examples: parenchymal cells of the liver and kidney; smooth muscle cells; vascular endothelial cells
• Permanent Cells
  • Do not undergo mitotic division; generally replaced with scar tissue
  • Examples: nerve cells, skeletal muscle, cardiac muscle

Question

• Is the following statement true or false?
• Permanent cells, once damaged, can easily be regenerated and their functions recovered.
  • False
• Rationale: Many cells in the body cannot be replaced once they die. Neurons and cardiac cells are such examples.

Stages of Wound Healing

• Inflammatory phase
  • Begins with tissue injury
  • Blood clots and WBC’s migrate to site of injury
  • Neutrophils arrive first to “clean things up”; macrophages arrive later
• Proliferative phase
  • Fibroblasts are predominant cells → these cells secrete the “stuff” that is needed to stimulate reconstruction the wound (collagen, vascular growth factors for angiogenesis, epithelial cells)
• Remodeling or maturational phase
  • Begins about 3 weeks following the injury
  • Scar formation occurs

Development of a New Capillary Vessel

• Proteolytic degradation of the parent vessel basement membrane, allowing for formation of a capillary sprout
• Migration of endothelial cells from the original capillary toward an angiogenic stimuli
• Proliferation of the endothelial cells behind the leading edge of the migrating cells
• Maturation of the endothelial cells and proliferation of pericytes (for capillaries) and smooth muscle cells (for larger vessels)

Healing by Primary or Secondary Intention

• The objective of the healing process is to fill the gap created by tissue destruction and to restore the structural continuity.
• Primary healing: small, clean wound
• Secondary healing: great loss of tissue with contamination; wound is generally left open to heal

Basic Components of the Extracellular Matrix (ECM)

• Fibrous structural proteins
  • Collagen and elastin fibers
• Water-hydrated gels that permit resilience and lubrication
  • Proteoglycans and hyaluronic acid
• Adhesive glycoproteins that connect the matrix elements to each other and to cells
  • Fibronectin and laminin

Basic Forms of the Extracellular Matrix

• Basement Membrane
  • Surrounds epithelial, endothelial, and smooth muscle cells
• Interstitial Matrix
  • Present in the spaces between cells the connective tissue and between the epithelium and supporting cells of blood vessels

Causes of Impaired Wound Healing

• Malnutrition
  • sufficient calories are necessary
• Impaired blood flow and oxygen delivery
  • nutrients have to get to the “scene of the accident”; cells need oxygen to survive
• Impaired inflammatory and immune responses
  • Frequent causes
    • diabetes mellitus
    • corticosteroids
• Would healing is delayed with
  • Infection
  • Wound separation
  • Foreign bodies
• Effects of age

Age Effects on Wound Healing

• Children
  • Greater capacity for repair than the adult population
  • Increased water content and skin laxity increases risk of wounds
  • May lack systemic reserves to promote healing
  • Electrolyte imbalances
  • Temperature instability
  • Lack of fully functional immune system in the very young child
  • Problems with obtaining adequate nutrition
  • Short gut syndrome; diabetes mellitus
• Elderly
  • Decreased dermal thickness and collagen content
  • Reduced fibroblast synthesis
  • Co-morbid illnesses: diabetes, vascular disease
  • Dietary insufficiency
    • Decreased arginine, zinc, protein and vitamin C intake
  • Changes in skin composition
  • Increased risk of pressure ulcers
    • Shifting every two hours
    • Pressure > 6 hours → ulceration → necrosis → infection → legal action

Question

• Which will promote wound healing?
  • B. Increased blood flow and oxygen delivery
• Rationale: Increasing blood flow and oxygen delivery is one of the main objectives of the inflammatory response. This will allow for greater energy production and faster removal of dead material.

Case Study Question 2: Leukocytosis

• In an acute response, leukocytosis occurs to increase the number of circulating white blood cells to support the immune response.
• The movement of white blood cells to the site of injury occurs as a result of chemotaxis.
• Margination and emigration are the events that describe the movement of circulating leukocytes from the blood to the injured tissue; local blood stasis allows leukocytes to move to the perimeter of vessels and pass (or emigrate) through capillary walls.
• Neutrophils arrive early to phagocytose microbes and cellular debris.
• Monocytes travel in the blood and migrate to injured tissue where they become macrophages.
• These cells are capable of engulfing greater quantities of foreign material and are able to move to the lymphatic system, where they prime specific immunity.

Case Study Question 3: Nutrition

• Nutrition plays an important factor in wound healing.
• What stages of Carlton’s wound healing would be affected by a deficiency in vitamins A and C?

Case Study Question 3: Vitamin Deficiencies

• Vitamin A and C assist collagen synthesis.
• Vitamin C has a direct influence on collagen assembly and the removal of by-products that result from collagen manufacturing
• A deficiency in vitamin C would therefore affect the onset of the proliferation stage and the effectiveness of the remodeling phase where collagen production and lay down are critical.
• Vitamin A stimulates capillary growth and epithelialization.
• A deficiency in vitamin A would hinder angiogenesis in the inflammatory phase of wound healing and epithelialization in the latter component of the proliferation phase.

Case Study Answers

1. What is the physiologic mechanism causing the wound to become red, hot, swollen, and painful? How is this different than the inflammatory response that might occur in an internal organ?
   • Carlton’s signs are typical of acute inflammation. Local vasodilation creates erythema and warmth. The edema is a result of increased vessel permeability and migration of exudate into the surrounding tissue. The engorgement of fluid at the area of injury contributes to the sensation of pain.
   • Visceral inflammation has a slightly different presentation: heat is less likely to occur because core temperature is preserved at a homeostatic level, and pain becomes apparent only when stretch receptors on the surfaces of the viscera are stimulated.
2. What are the immunologic events that are happening at the local level during Carlton’s acute inflammatory response?
   • In an acute response, leukocytosis occurs to increase the number of circulating white blood cells to support the immune response. The movement of white blood cells to the site of injury occurs as a result of chemotaxis. Margination and emigration are the events that describe the movement of circulating leukocytes from the blood to the injured tissue; local blood stasis allows leukocytes to move to the perimeter of vessels and pass (or emigrate) through capillary walls. Neutrophils arrive early to phagocytose microbes and cellular debris. Monocytes travel in the blood and migrate to injured tissue where they become macrophages. These cells are capable of engulfing greater quantities of foreign material and are able to move to the lymphatic system, where they prime specific immunity.
3. Nutrition plays an important factor in wound healing. What stages of wound healing would be affected by a deficiency in vitamins A and C?
   • While the components of nutritional intake are valuable to all stages of wound healing, some have more specific qualities. Both vitamin A and C assist collagen synthesis, but vitamin C has a direct influence on collagen assembly and the removal of by-products that result from collagen manufacturing. A deficiency in vitamin C would therefore affect the onset of the proliferation stage and the effectiveness of the remodeling phase where collagen production and lay down are critical. Vitamin A stimulates capillary growth and epithelialization. A deficiency in vitamin A would hinder angiogenesis in the inflammatory phase of wound healing and epithelialization in the latter component of the proliferation phase.