Cellular Reactions and Adaptations Quiz

Cellular Reactions to Injury

• Cell injury underlies all diseases. Understanding diseases begins with understanding cell injury.
• When a cell is exposed to an injurious agent, one of three outcomes can occur:
  • The cell may correct the situation.
  • The cell may experience a reversible injury.
  • The cell may experience an irreversible injury and die via necrosis or apoptosis.
• The outcome depends on the type, severity, and duration of the injury, and the type of cell.

Cellular Adaptation

• Cellular adaptation is the ability of cells to adjust their structure and function in response to changes in their environment or stressors.
• Adaptation aims to enhance survival and maintain homeostasis.

Types of Cellular Adaptation

• Hypertrophy: An increase in the size of cells. Increased workload leads to increased protein synthesis, increased size and number of intracellular organelles, which subsequently increases the size of the cell and the organ. Examples include enlargement of the left ventricle in hypertensive heart disease, and skeletal muscle increase during workload exercise.
• Hyperplasia: An increase in the number of cells. Usually caused by hormonal stimulation. Can be physiological, such as breast enlargement during pregnancy, or pathological, such as benign prostatic hyperplasia (BPH).
• Atrophy: A decrease in the size of a cell, leading to a decreased size of the organ. This can be caused by disuse, malnutrition, decreased endocrine stimulation and denervation (lack of communication between nerve and muscle). Autophagic vacuoles, containing degraded organelles, are found in atrophic cells.
• Metaplasia: Replacement of one differentiated tissue with another differentiated tissue.
  • Squamous metaplasia: Replacement of columnar epithelium with squamous epithelium, for instance, in the bronchi of smokers.
  • Osseous metaplasia: Replacement of connective tissue with bone, such as at sites of injury.

Reversible Cellular Changes & Accumulations

• Fatty Change: Accumulation of triglycerides within parenchymal cells (e.g., hepatocytes, alveolar cells, renal tubular cells, cardiomyocytes). Fatty change is commonly seen in the liver, heart, and kidneys. Factors like alcohol, diabetes mellitus, malnutrition, obesity, and poisonings can cause this. Mechanisms leading to fat accumulation include:
  • Increased uptake of triglycerides into parenchymal cells.
  • Decreased use of fat by cells.
  • Overproduction of fat in cells.
  • Decreased secretion of fat from cells.
• Pigment Accumulation: Accumulation of pigments, which can be exogenous (from outside the body) or endogenous (produced inside the body).
  • Endogenous pigments: Melanin (brownish-black pigment produced by melanocytes), bilirubin (yellowish pigment from hemoglobin breakdown), hemosiderin (iron-containing pigment from ferritin), and lipofuscin (pigment inside lysosomes).
  • Exogenous pigments: Carbon (coal dusts in lungs and lymph nodes - anthracosis), and injected pigments (tattoos).

Cell Death

• Necrosis: Death of a cluster of cells.

  • Results from excess fluid entering the cell, causing swelling and rupture of the cell membrane.
  • Intracellular degradative reactions occur in a living organism, not a dead one.
  • Autolysis and heterolysis take place in dead organisms.
  • Types of necrosis:
    • Coagulative necrosis: Most commonly results from sudden blood supply interruption. Characterized by preservation of tissue structure, marked by nuclear changes (pyknosis, karyorrhexis, karyolysis).
    • Liquefactive necrosis: Dissolution (softening and liquefaction) of tissue. Often seen in the central nervous system (CNS) and in abscesses.
    • Fat necrosis: Damage to tissues with high fat content often resulting from trauma or acute hemorrhagic pancreatitis.
    • Caseous necrosis: Appearance described as cheese-like (caseous, white). Seen in some bacterial infections and tuberculous lesions.
    • Gangrenous necrosis: Involves death of tissue due to vascular occlusion, often in lower extremities or bowel. Can be wet (with superimposed bacterial infection and liquifactive necrosis) or dry (with coagulative necrosis).

• Apoptosis: Death of individual cells within clusters.

  • Characterized by cell shrinkage and fragmentation into apoptotic bodies.
  • Plays a crucial role in development, tissue homeostasis, and removing damaged cells.

Pathological Calcification

• Metastatic calcification: Caused by hypercalcemia (elevated calcium levels in the blood), often from disorders like hyperparathyroidism.
• Dystrophic calcification: Occurs in damaged tissues, regardless of serum calcium levels. Examples include areas of old injuries, scarred tissue, and some forms of atherosclerosis.

Test your knowledge on cellular reactions to injury and adaptation mechanisms. Explore how cells respond to various stressors and the implications of different injury outcomes. This quiz covers essential concepts critical to understanding cell biology.