Cellular Injury, Adaptations, and Maladaptive Changes

Etiologic Factors and Cellular Changes

  • Etiologic factors can cause cells to undergo adaptive and maladaptive changes, altering normal function.

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

  • Different etiologic agents cause dysfunction and change the cellular environment.

  • Homeostasis can be maintained during temporary stressors, but prolonged or severe stressors can disrupt it.

Cellular Adaptations and Maladaptive Changes

  • Cellular adaptations and maladaptive changes result from disease processes, altered cell function, or environmental influences.

  • Histology: The study of tissues and cells for diagnostic information.

  • Biopsy: Extraction of a cell sample for histological examination.

Cellular Adaptations

Atrophy

  • Cells revert to a smaller size in response to environmental changes.

  • Occurs when the environment cannot support the cell's metabolic demands.

  • Smaller size = less metabolic demand, enhancing cell survival.

  • Common in paralysis due to loss of muscle contraction, nerve stimulation, and workload.

  • Causes of Atrophy

    • Disuse or diminished workload

    • Lack of nerve stimulation (paralysis)

    • Loss of hormonal stimulation

    • Inadequate nutrition

    • Decreased blood flow (ischemia)

    • Aging

Hypertrophy

  • Increase in individual cell size, resulting in enlargement of functional tissue.

  • Increased functional components lead to increased metabolic demand and energy needs.

  • Physiological hypertrophy: Enlarged muscle adequately supplied with blood flow, oxygen, and nutrients (e.g., in well-trained athletes).

  • Pathological hypertrophy: Increase in cell size without a corresponding increase in supporting structures (e.g., in hypertension, heart works harder to pump blood).

Hyperplasia

  • Increase in the number of cells within a tissue or organ.

  • Occurs in tissues capable of miotic division (e.g., epithelium, glandular tissue).

  • Stimulated by cellular mechanisms or hormonal stimulation (e.g., estrogen stimulation during pregnancy).

Metaplasia

  • Replacement of one cell type by another.

  • Result of genetic reprogramming in response to environmental changes.

  • Typically occurs in chronic inflammation and GERD.

  • In GERD, stomach acid refluxes into the esophagus, irritating cells. Squamous epithelium cells transform into columnar stomach-like cells.

Dysplasia

  • Deranged cellular growth within a specific tissue, often due to chronic inflammation or precancerous conditions.

  • Dysplastic cells vary in size and shape compared to healthy cells.

  • Cervical dysplasia is a common example; frequent exams are necessary as it is a precursor to cervical cancer.

Neoplasia

  • New growth; disorganized, uncoordinated, uncontrolled proliferative cell growth that is cancerous.

  • Tumor and neoplasm are synonymous, indicating new cells growing within a tissue or organ.

  • Classified as benign or malignant based on differentiation (the process where new cells acquire the structure/function of the cells they replace).

  • In malignant melanoma, neoplastic epithelial cells replace normal epithelial cells.

  • Cellular differentiation categorizes neoplasms

    • Benign neoplasms: Well-differentiated cells that resemble normal healthy cells and do not metastasize.

    • Malignant neoplasms: Poorly differentiated cells that break away from the tissue of origin and metastasize to adjacent sites, forming secondary neoplasms.

Basic Concepts of Cellular Injury

  • Cell injury occurs when cells are exposed to severe stress, preventing them from maintaining homeostasis.

  • Basic changes include

    • Dysfunction of the sodium/potassium pump

    • Loss of membrane integrity

    • Mitochondrial dysfunction

    • Defects in protein synthesis

    • Intracellular accumulations

    • Cellular swelling

    • DNA damage

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

  • Reduced ATP production impairs cellular physiological functions.

  • Lack of ATP leads to failure of the Na+/K+ pump, which is crucial for membrane polarity in muscle cells and neurons.

  • Improper pump function increases intracellular sodium ion concentration, leading to water retention and cellular swelling.

  • Lack of ATP also affects the calcium pump, causing intracellular calcium accumulation, disrupting biochemical processes, ATP depletion, plasma membrane damage, and DNA disruption.

  • Pathological calcification: Deposition of calcium within tissues, often in areas of cell injury and death.

Loss of Plasma Membrane Integrity

  • The plasma membrane protects internal organelles.

  • Disruption allows injurious agents to affect organelles, and water can enter causing swelling.

  • Damage to mitochondria stops energy production, leaving the nucleus vulnerable.

Defects in Protein Synthesis

  • Low ATP levels decrease protein synthesis.

  • Cells cannot regenerate, and many bodily processes malfunction.

  • Lack of protein synthesis leads to cell degeneration or death.

Intracellular Accumulations

  • Excessive accumulation of substances such as cell components, environmental substances, and cell breakdown products.

  • Accumulations can be harmless or toxic.

  • Controllable accumulations may cause reversible effects; uncontrollable accumulations cause cell injury.

  • Example: Alcohol exposure can cause intracellular fat accumulation in the liver (fatty liver), leading to enlargement and dysfunction.

DNA/Genetic Damage

  • Injury to DNA causes mutations, changing cell structure and function.

  • Mutated DNA is transcribed into mutated mRNA, which directs ribosomes to produce abnormal proteins.

  • Abnormal proteins rebuild the cell abnormally, resulting in abnormal secretions.

Stressors and Injurious Agents

  • Hypoxic cell injury

  • Free radical injury (oxidative stress)

  • Physical agents of injury

  • Chemical injury

  • Infectious agent injury

  • Injurious immunological reactions

  • Genetic defects

  • Nutritional imbalances

Hypoxic Cell Injury

  • Hypoxia (lack of oxygen) is the most common cause of cell injury.

  • Often results from ischemia (diminished blood circulation).

  • Arterial obstruction can be caused by atherosclerotic plaque and blood clot formation.

Free Radical Injury

  • Cells generate energy via oxidative phosphorylation, producing small amounts of oxygen molecules (free radicals).

  • Free radicals are present in environmental substances (e.g., cigarette smoke, pesticides).

  • They penetrate the plasma membrane and disrupt internal organelles, damaging DNA.

  • Damage caused by free radicals is known as oxidative stress, resulting in cell injury.

  • Common in cells undergoing transient ischemia; cell death can occur after blood flow is restored due to damaging free radicals.

Physical Agents of Injury

  • Mechanical trauma (lacerations, gunshot wounds, falls).

  • Temperature extremes, burns, frostbite, radiation, electrical shock.

  • Physiological responses to trauma (e.g., inflammation) can lead to healing or further cell damage.

Chemical Injury

  • Caused by endogenous (internal) or exogenous (external) substances.

  • Chemical agents damage the plasma membrane and cause dysfunction in organelles.

  • Imbalances of internal chemical constituents (e.g., electrolytes) can cause cell injury.

  • High sodium levels can cause intracellular fluid depletion, leading to cellular dehydration.

  • Exogenous substances (drugs, pollutants, poisons) can cause cell injury.

  • NSAIDs and antibiotics can be nephrotoxic (damaging to kidney nephron tubules).

  • In carbon monoxide poisoning, carbon monoxide binds tightly to hemoglobin, reducing oxygen delivery to tissues.

Infectious Agents of Injury

  • Microorganisms (bacteria, viruses, fungi, parasites) cause cellular injury.

  • Helicobacter pylori causes peptic ulcer disease, eroding the gastrointestinal mucosal lining and damaging underlying cells.

  • Constant acidic irritation leads to ulceration of gastrointestinal cells (peptic ulcer).

Injurious Immunological Reactions

  • The immune system can overreact and attack the body's own cells (autoimmune conditions).

  • In rheumatoid arthritis, immune system cells attack the body's joints.

Genetic Defect

  • Genetic disorders damage and mutate DNA, leading to cell injury.

  • Damaged DNA is transcribed as defective RNA, which transmits flawed instructions to ribosomes.

  • Ribosomes produce abnormal cellular proteins, initiating disease.

Nutritional Imbalances

  • Undernutrition, overnutrition, and malnutrition can cause cell injury.

  • Starvation leads to inadequate nutrient supplies needed for normal cell function.

  • Insufficient proteins, carbs, fats, vitamins, and minerals cause cell dysfunction.

  • Protein starvation can lead to marasmus and kwashiorkor.

Cell Degeneration and Death

  • Apoptosis and necrosis are two major forms of cell death.

  • Apoptosis: Programmed cell death without adverse effects on the body.

  • Necrosis: Cell death caused by injury, leading to dysfunction and adverse effects on neighboring tissues and organs.

Apoptosis

  • Genetically programmed degenerative change resulting in cell death.

  • Organized process that eliminates unwanted cells without inflammation.

  • Example: Ovaries degenerate during menopause.

Necrosis

  • Cells die as a result of stressors overwhelming their ability to survive.

  • Irreversible process involving membrane disintegration, lysosomal disruption, and cell death.

  • Example: Infarction (death of cardiac muscle tissue due to prolonged ischemia).

  • Lack of coronary artery blood supply results in ischemia; prolonged ischemia leads to infarction.

  • Lysosomal enzymes and proteins from dead cardiac cells are released into the bloodstream.

  • Gangrene: Tissue necrosis that can develop after cell death, often seen in patients with peripheral arterial disease (PAD) of the lower extremities.

Clinical Interventions to Reverse Cell Injury

  • Removal of injurious stimuli can reverse muscle atrophy.

  • Restoration of circulation or nerve stimulation can allow rehabilitation of normal cell size.

  • Neoplastic growths usually require surgical removal.

  • Malignant neoplasms require intense treatment modalities like radiation and chemotherapy.

Interventions to Treat Permanent Cell Injury

  • Treatments are limited.

  • Example: Heart muscle cells die during myocardial infarction and are assumed to be permanently dysfunctional.

  • Future heart complications can ensue depending on the amount of cardiac muscle tissue affected.

  • Interventions include

    • Organ and tissue transplantation

    • Regenerative medicine using stem cells

    • Therapeutic cloning

Transplantation

  • Surgical intervention that replaces injured cells, tissues, and organs with viable donor tissue.

  • Involves donor solicitation, organ harvesting, matching, surgical implantation, and interventions to prevent organ rejection.

  • Effective for conditions like kidney failure, heart failure, pancreatic and liver disease, and bone marrow transplants.

Regenerative Medicine Using Stem Cells

  • New methods of cellular regeneration involving stem cells.

  • Past research focused on human embryonic stem cells, which raised ethical issues about destroying potential human life; the approach was banned in the U.S.

  • Alternative methods of deriving stem cells have been developed due to the controversy of using embryos.

Umbilical Cord Blood (UCB)

  • Rich source of stem cells supplied by the placenta.

  • Transplant of UCB stem cells shows promise for children with hematological cancers.

  • Bone marrow stem cell transplants require donor-recipient matching, while UCB transplants can be derived from any woman during childbirth, making the supply almost limitless.

Therapeutic Cloning

  • Cloning technology and stem cell research are under investigation for the creation of transplant organs.

  • Combines cloning technology and stem cell transplantation.

  • Has the potential to develop new organs using human somatic cells without the use of a human embryo.