Module 4

Cellular Injury, Adaptations, and Maladaptive Changes

Disease Etiology

  • Etiology: The original cause of cell alteration or disease.

    • Etiologic agents: The specific causes of the cell alteration or disease, which can include:

    • Infection

    • Trauma

  • Characteristic changes with specific etiologic agents:

    • Example: Cold temperature causes frostbite.

    • Example: Streptococcal bacteria cause sore throat.

  • In response to an etiologic agent, a cell may:

    • Develop adaptive, compensatory changes.

    • Develop maladaptive changes.

Basic Terminology

  • Histology: The microscopic study of tissue.

  • Biopsy: A sample taken from an organism for histological analysis.

  • Autopsy: The examination of tissue from deceased organisms.

  • Pathognomonic changes: Unique, identifying presentations of a disease.

    • Example: A crater-like formation in the stomach suggests the presence of an ulcer.

Basic Cellular Adaptations and Maladaptive Changes

  • Cellular adaptations include:

    • Atrophy: Reduction in cell size.

    • Example: Paralysis leading to the shrinkage of skeletal muscle.

    • Hypertrophy: Increase in individual cell size.

    • Example: Strength training.

    • Hyperplasia: Increase in the number of cells, but only in cells capable of mitosis.

    • Example: Estrogen stimulating the growth of breast cells during pregnancy.

    • Metaplasia: Replacement of one cell type with another, ensuring cell survival.

    • Example: In GERD, squamous epithelium in the esophagus transitions to columnar cells, resembling stomach cells.

    • Dysplasia: Abnormal cell growth, often due to chronic inflammation or precancerous conditions.

    • Example: Cervical dysplasia detected via Papanicolaou (Pap) test.

    • Neoplasia: Describes new, disorganized, uncontrolled growth, often equated with cancer; neoplasms may be benign or malignant.

Atrophy and Hypertrophy

  • Atrophy:

    • Definition: Cells revert to a smaller size.

    • Example: Muscle shrinkage from paralysis.

  • Hypertrophy:

    • Definition: Increase in cell size.

    • Physiological: Cell enlargement with adequate supporting structures.

    • Example: Enlargement of cardiac cells due to exercise training.

    • Pathological: Increase in cell size without adequate support structure.

    • Example: Cardiac tissue enlargement due to hypertension.

Hyperplasia

  • Definition: Increase in the number of cells; occurs only in cells capable of mitosis.

  • Mechanism: Often results from hormonal stimulation.

    • Example: Estrogen during pregnancy.

  • Maladaptive compensation can occur if cell number increases excessively.

    • Example: Formation of keloids.

Metaplasia

  • Definition: Replacement of one cell type with another through genetic reprogramming for survival.

    • Example: In GERD, lower esophageal cells transition from squamous to columnar epithelium due to acid exposure.

Dysplasia

  • Definition: Deranged cellular growth which often results from chronic inflammation or predisposed states.

    • Cells exhibit varying sizes, shapes, and organization compared to normal cells.

    • Example: Cervical dysplasia as identified through a Pap test.

Neoplasia

  • Definition: Represents “new growth”, characterized by disorganized, uncontrolled proliferation and is usually termed as “cancerous.”

  • Neoplasms can be:

    • Benign: Resemble normal cells, well-differentiated, do not metastasize, possess well-defined borders.

    • Malignant: Appear different from healthy cells, poorly differentiated, higher risk for metastasis, possess poorly defined borders.

Basic Concepts of Cell Injury

  • Cellular Disruption leads to:

    • Dysfunction of the Na+/K+ pump -> Disruption of electrochemical gradient.

    • Cellular swelling due to dysfunction of Ca++ pump -> Accumulation of intracellular Ca++ leading to cell degeneration.

    • Loss of plasma membrane integrity opens the barrier for harmful agents to enter.

    • Defects in protein synthesis can result in cell death through necrosis.

    • Intracellular accumulations disrupt cell functioning (e.g., fatty liver, xanthomas).

    • Genetic damage through DNA mutations.

Intracellular Accumulations

  • Distinguishing between conditions:

    • Normal Liver vs. Fatty Liver

    • Xanthelasma: Cholesterol deposit conditions beneath the skin.

Causes of Cell Injury

  • Hypoxia: Diminished oxygen delivery to cells; most common cause leading to cell injury, affecting

    • Result due to ischemia, anemia, or pulmonary issues, triggering anaerobic metabolism and increasing lactic acid levels.

  • Free radical injury: Reactive species formed during metabolism that disrupt cellular membranes.

    • Overwhelmed protective mechanisms lead to oxidative stress.

  • Physical agents: Examples include:

    • Lacerations, falls, burns, electrical shock.

  • Chemical injury:

    • Endogenous: e.g., elevated ions, high blood glucose.

    • Exogenous: e.g., drugs, pollutants, smoking.

  • Infectious agents: Pathogens such as bacteria, fungi, and parasites.

  • Injurious immunological reactions: Can include autoimmune diseases and chronic inflammation.

  • Nutritional imbalances: Necessary macromolecules, vitamins, and minerals are essential for cell function.

Endothelium and Its Injury

  • The endothelium lines the interior of vessels and is active tissue that secretes substances like VEGF and NO (nitric oxide).

  • Injury effects: May lead to conditions such as atherosclerosis.

    • Common agents causing injury include:

    • Hypertension

    • Hyperglycemia

    • Free radicals

    • Hyperlipidemia

Mechanisms of Endothelial Injury

  • Hypertension: Creates excessive shearing forces potentially leading to aneurysm.

  • Diabetic hyperglycemia: Glucose reacts with the endothelium leading to damage via advanced glycation end products.

  • Free radicals: Highly reactive molecules injuring the endothelium, further escalated by cigarette smoking.

  • Low-Density Lipoprotein Cholesterol (LDL-C): Key player in atherogenesis, where LDL accumulates leading to foam cell formation and plaque development.

Atherogenesis and its Effects

  • Atherosclerosis begins with endothelial injury which attracts LDL molecules; the accumulation leads to foam cell formation.

  • Progressive stages include:

    • Initial lesion

    • Fatty streak

    • Intermediate lesion

    • Atheroma

    • Fibrous plaque

    • Complicated lesion

Types of Cell Degeneration

1. Apoptosis

  • Definition: Programmed cell death that occurs in a regulated fashion, not causing inflammation or harming surrounding tissues.

  • Associated dysfunctions may occur in diseases like prostate cancer or spinal muscular atrophy.

2. Necrosis

  • Definition: Cell death resulting from injury, representing an irreversible process.

  • Characterized by disintegration of the membrane and activation of lysosomes leading to inflammation.

3. Infarction

  • Definition: Ischemic necrosis, where prolonged ischemia causes tissue death.

    • Example: Myocardial infarction (heart attack) leads to the release of cardiac proteins into circulation.

4. Gangrene

  • Definition: Prolonged ischemia, infarction, and resultant necrosis.

    • Example: Clostridium perfringens causes gas gangrene, identifiable by gas emissions as tissues are destroyed.

Interventions to Prevent Cell Injury

  • Transplantation: Replacement of organs or healthy tissues; issues include short supply, donor matching, and rejection.

  • Regenerative medicine: Utilizing stem cells, specifically human umbilical cord-mesenchymal stem cells (HUC-MSCs). These stem cells have:

    • Remarkable proliferative and differentiating ability, low immunogenicity, and therapeutic application in over 10 diseases.

Check Your Knowledge

  • Identify which definitions are incorrect:

    • Dysplasia: Incorrect as it is not merely a transformation of cell type but a derangement in growth.

    • Hyperplasia: Correct as it indicates an increase in cell number.

    • Malignancy: Correct as it suggests uncontrollable growth with spreading potential.

    • Hypertrophy: Correct as it indicates increased muscle fiber size.

Inflammation and Dysfunctional Wound Healing

Overview of Inflammation

  • Definition: A coordinated response aimed at containing an injury.

  • Goals include:

    • Wall off the injured area.

    • Prevent the spread of the injury.

    • Mobilize defenses.

  • Types of inflammation:

    • Local vs. systemic.

    • Acute vs. chronic.

Five Classic Signs of Inflammation

  1. Rubor (Redness)

  2. Tumor (Swelling)

  3. Calor (Heat)

  4. Dolor (Pain)

  5. Loss of function (Function laesa)

Phases of Acute Inflammation

Two Phases:

  1. Vascular phase:

    • Initial vasoconstriction.

    • Increased vascular permeability.

  2. Cellular phase:

    • Signals attract WBCs to the area of injury.

    • Activation of WBCs leads to their clearance of debris.

Mechanism of Vascular Permeability

  • Mediators: Histamine and bradykinin are crucial for vasodilation, promoting WBC travel to the injury site, aiding in toxin dilution.

  • Outcomes include:

    • Purulent exudate: Contains pus with proteins and microbes.

    • Transudate: Clear, watery fluid (e.g., blisters).

    • Abscess: Localized and walled-off collection of purulent exudate.

    • Effusion: Build-up of fluid within body cavities (e.g., pericardial effusion).

White Blood Cells in Inflammation

  • Chemotaxis: Attraction of WBCs to signals in the injury zone.

  • Leukocytosis: Increase in WBC count over the normal range (4,000 to 10,000 cells/mL).

  • Margination: Adherence of WBCs along the endothelium.

  • Types of leucocytes:

    • Neutrophils: First responders within 6-24 hours, predominant at acute sites.

    • Monocytes: Replace neutrophils after 24-48 hours transforming into macrophages.

  • Inflammatory mediators: Released from tissues, modulating inflammation through cytokines such as TNF-alpha and interleukins.

Acute Phase Proteins

  • Produced by the liver, including:

  • C-Reactive Protein (CRP): Marks foreign materials for phagocytosis and indicates active inflammation when elevated.

  • Fibrinogen: Binds to red blood cells, affecting their formation in rouleaux phenomenon.

  • Serum amyloid A: Associates with chronic inflammation and amyloidosis.

  • Hepcidin: Elevation signifies reduced iron storage during chronic inflammation.

Systemic Responses in Acute Inflammation

  • Symptoms may include:

    • Fever, lymphadenopathy, and a host of effects that lead to weight loss and lethargy.

Fever Mechanism

  • Pyrogens released from WBCs cause a reset of the hypothalamic temperature set point, leading to increased body temperature, which enhances WBC performance.

Lymphadenopathy

  • Definition: Enlargement of lymph nodes due to inflammatory processes.

    • Indicates the activation of lymphocytes in response to injurious agents.

Histamine Release

  • Released from basophils, platelets, and mast cells, causing vasodilation and increased venule permeability leading to symptoms like a runny nose.

Prostaglandins and Leukotrienes

  • Formed from phospholipid breakdown pathways and contribute to inflammation and pain.

Outcomes of Acute Inflammation

  • Outcomes include:

    • Complete resolution of inflammation with potential for normal healing through regeneration or fibrosis.

    • Chronic inflammation occurs when resolution fails, resulting in extensive tissue damage.

Chronic Inflammation

  • Defined by persistent infections or hypersensitivity reactions.

  • Characterized by a predominance of monocytes, macrophages, and continuous cytokine release, damaging healthy tissues.

Non-Pharmacological Treatments for Inflammation

  • Cryotherapy: Cold therapy to reduce pain and inflammation; recommended for acute inflammation.

  • Heat therapy: Enhances blood flow and tissue elasticity; useful for chronic conditions.

  • Alternative therapies: May include herbs and techniques like yoga and acupuncture.

Pharmacological Treatments

  • Corticosteroids: Target phospholipase enzymes to inhibit inflammatory mediators but carry adverse effects.

  • NSAIDs: Block COX pathways affecting inflammation and pain levels.

Wound Healing Processes

  1. Hemostasis: Immediate cellular response following tissue injury, leading to clot formation and initial inflammation.

  2. Inflammation: Initial recruitment of immune responses to clear debris.

  3. Cellular processes: Include fibroblast activity, angiogenesis, and epithelization dive into scar formation.

Types of Wound Healing Intentions

  • Primary Intention: Clean edges; rapid epithelialization.

  • Secondary Intention: Extensive tissue loss with scarring and delayed closure.

  • Tertiary Intention: Large tissue loss requiring prolonged healing and often surgical intervention.

Factors Affecting Wound Healing

  • Nutrition, oxygen levels, immune function, infection, and mechanical factors can significantly affect healing outcomes.

Dysfunctional Wound Healing

  • Types of dysfunction include:

    • Wound dehiscence: Re-opening of previously closed wounds.

    • Keloid formation: Overgrowth of scar tissue from excess epithelialization.

    • Contractures: Inflexibility reducing movement capabilities.

    • Fistula: Abnormal connections between structures.

    • Adhesions: Bands of scar tissue that limit mobility.