Week 1 Chapter 2 Cell Injury & Maladaptive changes

CAPRIOTTI - DAVIS ADVANTAGE for PATHOPHYSIOLOGY

Introductory Concepts and Clinical Perspectives

Overview

  • Second Edition of the textbook published by F.A. Davis Company (2020).

  • Focus on personalized learning and quizzing through the Davis Advantage platform.

Chapter 2: Cell Injury, Adaptations, and Maladaptive Changes

Disease Etiology

Etiology

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

  • Etiologic Agents: Factors that cause cell alteration or disease.

    • Examples include:

    • Infection

    • Trauma

Characteristic Changes with Specific Etiologic Agents

  • Cells exhibit specific changes based on etiologic agents:

    • Cold Temperature: Causes frostbite.

    • Streptococcal Bacteria: Causes sore throat.

Cellular Responses to Etiologic Agents

  • In response to etiologic agents, cells may undergo:

    • Adaptive Changes: Compensatory modifications to function.

    • Maladaptive Changes: Alterations that lead to dysfunction.

Basic Terminology

Histology

  • Definition: The microscopic study of tissue.

Biopsy

  • Definition: A sample taken for histological analysis.

Autopsy

  • Definition: Examination of tissue from deceased organisms.

Pathognomonic Changes

  • Definition: Unique disease presentations that are indicative of specific conditions.

    • Example: Crater-like formation in the stomach indicating an ulcer.

Basic Cellular Adaptations

Atrophy

  • Definition: Cells revert to a smaller size due to a reduction in metabolic demand.

    • Example: Paralysis can cause shrinkage of skeletal muscle.

Hypertrophy

  • Definition: Increase in individual cell size.

Types of Hypertrophy

  • Physiological Hypertrophy:

    • Cell enlargement with adequate supporting tissues.

    • Example: Enlargement of cardiac cells with exercise training.

  • Pathological Hypertrophy:

    • Increase in cell size without an increase in support structures.

    • Example: Enlargement of heart tissue due to hypertension.

Hyperplasia

  • Definition: Increase in the number of cells, occurring only in cells that can undergo mitosis.

  • Causes of hyperplasia include hormonal stimulation.

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

  • Maladaptive Compensation: Excessive hyperplasia may result in conditions such as keloid formation.

Metaplasia

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

    • Example: In GERD, lower esophageal cells transform from squamous epithelium to columnar stomach-like cells.

Dysplasia

  • Definition: Deranged cellular growth, often a result of chronic inflammation or precancerous conditions.

  • Characterized by variability in size, shape, and organization compared to normal cells.

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

Neoplasia

  • Definition: “New growth” characterized by disorganized, uncoordinated, and uncontrolled cell growth, often referred to as "cancerous".

  • Neoplasm: Often interchangeably used with the term “tumor”.

  • Neoplasms can be:

    • Benign:

    • Resemble normal cells, well-differentiated, do not metastasize, and have well-defined borders.

    • Malignant:

    • Appear different from healthy cells, poorly differentiated, have an increased likelihood of metastasis, and poorly defined borders.

Basic Concepts of Cell Injury

Dysfunction of Sodium-Potassium Pump

  • Results in loss of electrochemical gradient.

    • Characteristics: Na+ accumulation leading to disrupted osmotic balance.

    • Lack of ATP results in intracellular Ca++ accumulation.

Loss of Plasma Membrane Integrity

  • Disruption of barrier causes:

    • Entry of harmful substances into the cell.

    • Loss of essential substances from the cell.

Defects in Protein Synthesis

  • Can potentially lead to cell death.

Intracellular Accumulations

  • Excessive deposits can disrupt cell function.

    • Examples include:

    • Fatty liver

    • Xanthomas and xanthelasma.

Genetic Damage

  • Injury to the cell's DNA may lead to mutations.

Causes of Cell Injury

Hypoxia

  • Definition: Diminished oxygen supply to cells.

  • Can result from:

    • Ischemia (diminished circulation)

    • Problems with RBC’s (e.g., anemia)

    • Pulmonary issues

  • Impact: Cells may enter anaerobic metabolism with increased lactic acid levels.

Free Radical Injury

  • Formed during aerobic metabolism and known as reactive oxygen species (ROS).

  • Characteristics:

    • Contain unpaired electrons which disrupt the plasma membrane.

    • Cells have protective mechanisms like enzymes and superoxide dismutases.

  • Oxidative Stress: Occurs when protective mechanisms are overwhelmed.

Physical Agents of Injury

  • Examples include:

    • Lacerations

    • Falls

    • Temperature extremes

    • Burns

    • Electrical shock.

Chemical Injury

  • Endogenous: Elevated ions; high blood glucose.

  • Exogenous: Drugs, pollutants, smoking.

Infectious Agents of Injury

  • Definition: Bacteria, fungi, and parasites that can cause cell damage.

Injurious Immunological Reactions

  • Examples include autoimmune diseases and chronic inflammation.

Nutritional Imbalances

  • Cells require proper amounts of macromolecules, vitamins, and minerals to function effectively.

Endothelium

Definition

  • Cells that line the interior of vessels.

  • Active tissue that secretes:

    • Vascular Endothelial Growth Factor (VEGF)

    • Nitric Oxide (NO)

    • Endothelin.

Injury Consequences

  • Injury to the endothelium may lead to conditions like atherosclerosis and can be caused by:

    • Hypertension

    • Hyperglycemia

    • Free radicals

    • Hyperlipidemia.

Endothelial Injury and Atherosclerosis

Hypertension

  • Impact: Creates a stronger-than-normal shearing force that can lead to aneurysm (a weakened area of the arterial wall that may rupture).

Diabetic Hyperglycemia

  • Mechanism: Glucose reacts with the endothelium, forming advanced glycation end products that further damage the endothelium.

  • Endothelin: A potent vasoconstrictor that is released during this process.

Free Radicals

  • Highly reactive oxidizing molecules that can injure the endothelium; cigarette smoking increases free radicals.

Persistent Angiotensin II Secretion

  • Fact: This potent vasoconstrictor increases blood pressure forces acting on the endothelium.

  • Elevated levels are often observed in heart disease.

Low-Density Lipoprotein (LDL) Cholesterol

Atherogenesis

  • Definition: The formation of atherosclerotic plaques initiated by endothelial injury.

  • Process:

    • Areas of endothelial injury attract LDL molecules.

    • LDL accumulates within macrophages to form foam cells.

    • Foam cells contribute to plaque formation, leading to further vessel blockage as endothelial NO levels decrease.

Cell Degeneration: Apoptosis

Apoptosis

  • Definition: Programmed cell death characterized as an organized process that does not cause inflammation or adversely affect surrounding tissues.

  • Associated Diseases:

    • Prostate cancer: decreased apoptosis.

    • Spinal muscular atrophy: increased apoptosis.

Cell Degeneration: Necrosis

Necrosis

  • Definition: Cell death resulting from injury that is an irreversible process characterized by membrane disintegration, lysosomal activation, and autolysis.

  • Impact: Initiates an inflammatory reaction.

Infarction

  • Definition: Ischemic necrosis where tissue death occurs due to prolonged ischemia.

  • Example: Myocardial infarction results in the release of cardiac proteins into circulation.

Apoptosis vs. Necrosis

  • Comparison:

    • Apoptosis:

    • Cell shrinks and chromatin condenses.

    • Apoptotic bodies are phagocytosed without causing inflammation.

    • Necrosis:

    • Cell swells and becomes leaky.

    • Cellular and nuclear lysis occurs, causing inflammation.

Cell Degeneration: Gangrene

  • Definition: Results from prolonged ischemia, infarction, and necrosis.

  • Example: Gangrene caused by Clostridium perfringens, which emits gas as it destroys tissues (gas gangrene).

Interventions to Prevent Permanent Cell Injury

Options Include

  • Transplantation: Replacement of organ or healthy tissue.

  • Regenerative Medicine: Utilizing stem cells for repair.

  • Therapeutic Cloning: Techniques to generate tissues and organs.

  • Reproductive Cloning: Method to create genetically identical organisms.

Chapter 2 More Detailed

Chapter 2: Cell Injury, Adaptations, and Maladaptive Changes
Disease Etiology

Etiology

  • Definition: The original cause of a cellular alteration or disease state. Understanding etiology is crucial for determining the appropriate clinical intervention.

  • Etiologic Agents: Factors that trigger cell alteration or disease.

    • Infection: Pathogenic microorganisms like viruses, bacteria, or fungi.

    • Trauma: Physical force causing structural damage.

    • Chemical Toxins: Endogenous or exogenous substances that disrupt biochemical pathways.

Characteristic Changes with Specific Etiologic Agents

  • Cells exhibit highly specific morphological and functional changes based on the nature of the stressor:

    • Cold Temperature: Leads to vasoconstriction and ice crystal formation within the cytosol, resulting in frostbite and potential necrosis.

    • Streptococcal Bacteria: Releases exotoxins that cause localized inflammation and cellular destruction in the oropharynx, presenting as a sore throat.

Cellular Responses to Etiologic Agents

  • In response to stressors, cells attempt to maintain homeostasis through:

    • Adaptive Changes: Compensatory modifications such as changing size or number to maintain function under new conditions.

    • Maladaptive Changes: Pathological alterations where the cell fails to compensate adequately, leading to cell death or dysfunction.

Basic Terminology

Histology

  • Definition: The microscopic study of tissues and cells to identify abnormalities in architecture or staining patterns.

Biopsy

  • Definition: A surgical procedure to extract a tissue sample for histological analysis, often used to differentiate between benign and malignant growths.

Autopsy

  • Definition: A post-mortem examination of tissues to determine the cause of death or the extent of disease progression.

Pathognomonic Changes

  • Definition: Characteristic histological or clinical findings that are unique to a specific disease, allowing for a definitive diagnosis.

    • Example: The presence of Negri bodies in brain tissue is pathognomonic for Rabies; a crater-like lesion in the gastric mucosa is pathognomonic for a peptic ulcer.

Basic Cellular Adaptations

Atrophy

  • Definition: A decrease in cell size due to a reduction in metabolic demand or loss of trophic stimuli.

    • Causes: Disuse (paralysis), denervation, loss of endocrine stimulation, ischemia, or inadequate nutrition.

    • Example: Disuse atrophy occurs in skeletal muscle when a limb is immobilized in a cast.

Hypertrophy

  • Definition: An increase in individual cell size, which increases the overall size of the organ. This occurs in tissues incapable of mitotic division (e.g., cardiac and skeletal muscle).

Types of Hypertrophy

  • Physiological Hypertrophy:

    • Characterized by cell enlargement accompanied by a proportional increase in supporting structures like blood vessels (angiogenesis) and nutrient supply.

    • Example: Left ventricular hypertrophy in an athlete due to aerobic training.

  • Pathological Hypertrophy:

    • Characterized by cell enlargement without a corresponding increase in metabolic support (capillaries or mitochondria).

    • Example: Cardiac hypertrophy due to chronic hypertension, where the heart wall thickens but the blood supply stays the same, leading to ischemia.

Hyperplasia

  • Definition: An increase in the absolute number of cells in a tissue or organ, occurring only in tissues capable of mitosis (e.g., epithelium and glandular tissue).

  • Mechanisms: Often driven by hormones or compensatory needs.

    • Example: Estrogen-driven hyperplasia of the uterine lining during the menstrual cycle.

  • Maladaptive Compensation: Keloids are a result of excessive hyperplasia of epithelial and connective tissue cells during wound healing.

Metaplasia

  • Definition: The replacement of one differentiated cell type with another cell type that is better suited to survive a chronic environmental stressor.

    • Example: In Barrett’s Esophagus, the normal stratified squamous epithelium of the lower esophagus changes to columnar epithelium (similar to stomach lining) to withstand the acidic environment of chronic GERD.

Dysplasia

  • Definition: Deranged cellular growth resulting in cells that vary in size, shape, and organization. This is often a precursor to neoplasia (precancerous).

    • Clinical Significant: Close monitoring is required; for example, cervical dysplasia discovered via a Pap smear requires follow-up to prevent cervical cancer.

Neoplasia

  • Definition: Uncontrolled, uncoordinated, and autonomous new cell growth. Neoplastic cells fail to respond to normal growth inhibitory signals.

  • Classification:

    • Benign: Well-differentiated (resemble the parent tissue), slow-growing, encapsulated, and stationary.

    • Malignant: Poorly differentiated (anaplastic), rapid growth, invasive, and capable of metastasis to distant organs.

Basic Concepts of Cell Injury

Dysfunction of Sodium-Potassium (Na^+/K^+) Pump

  • Fatigue of the pump due to lack of ATP prevents the removal of three Na^+ ions and the intake of two K^+ ions.

  • Outcome: Intracellular Na^+ concentrations rise, causing water to enter the cell by osmosis (cellular swelling or edema).

  • Additionally, the failure of the Ca^{++}/Mg^{++} ATPase pump leads to an influx of Calcium (Ca^{++}), which activates degradative enzymes that damage the cell membrane and DNA.

Loss of Plasma Membrane Integrity

  • When the membrane is breached, the controlled environment of the cell is lost. Lysosomal enzymes may leak into the cytoplasm and digest the cell from within.

Defects in Protein Synthesis

  • If the ribosomes or endoplasmic reticulum are damaged (often by hypoxia), the cell cannot produce essential proteins for repair or enzyme function, leading to failure and death.

Intracellular Accumulations

  • Cells may accumulate metabolically active or inactive substances:

    • Lipids: Fatty liver (steatosis) due to alcohol abuse.

    • Calcifications:

    • Dystrophic: Occurs in dead or dying tissues (e.g., calcified heart valves).

    • Metastatic: Occurs in normal tissues due to hypercalcemia.

Causes of Cell Injury

Hypoxia

  • Definition: Oxygen deprivation at the cellular level, the most common cause of cell injury.

  • Primary Cause: Ischemia (reduced blood flow), which is more damaging than hypoxia alone because it also prevents the removal of metabolic wastes.

  • Impact: Shift to anaerobic metabolism, which produces only 2 ATP (compared to 36 via aerobic) and creates lactic acid, lowering intracellular pH.

Free Radical Injury

  • Mechanism: Reactive Oxygen Species (ROS) possess an unpaired electron, makes them highly unstable. They damage cell membranes via lipid peroxidation and disrupt proteins and DNA.

  • Countermeasures: Superoxide dismutase, Vitamin A, C, and E, and beta-carotene act as antioxidants to neutralize ROS.

Endothelial Injury and Atherosclerosis

  • The endothelium is more than a lining; it is an endocrine organ.

  • Hypertension: High shearing force damages the endothelial slab, leading to weakened vessel walls or aneurysms.

  • Hyperglycemia: High glucose levels lead to the formation of Advanced Glycation End-products (AGEs), which trigger inflammation and vasoconstriction via Endothelin release.

  • LDL and Foam Cells: Endothelial injury allows LDL to enter the subendothelial space. Macrophages ingest the LDL and transform into Foam Cells, which are the building blocks of atherosclerotic plaques.

Cell Death Pathways

Apoptosis

  • Mechanism: A genetically programmed 'cell suicide'. It involves the activation of caspases that neatly break down the cell internals. Phagocytes remove the resulting apoptotic bodies without triggering an inflammatory response.

Necrosis

  • Mechanism: Accidental cell death caused by external stressors (ischemia, toxins). The cell swells and bursts (lysis), releasing lysosomes and inflammatory mediators into the surrounding tissue.

  • Infarction: A specific type of ischemic necrosis; for example, a myocardial infarction (heart attack) results in the irreversible death of cardiac myocytes.

Gangrene

  • Dry Gangrene: Result of chronic ischemia; tissue becomes dark and shriveled.

  • Wet Gangrene: Superimposed bacterial infection (liquefactive necrosis).

  • Gas Gangrene: Caused by Clostridium perfringens, an anaerobic bacteria that produces foul-smelling gases and rapidly destroys tissue.