Cell Injury and Death Overview

Overview of Cellular Responses to Stress and Noxious Stimuli

• Adaptations in cells are reversible changes to structural and functional states due to physiological or pathological stimuli, enabling survival and continued function.

Causes of Cell Injury

• Oxygen deprivation includes hypoxia due to ischemia (loss of blood supply) and anemia (decreased hemoglobin).
• Physical agents causing injury include mechanical trauma, temperature extremes (burns/freezing), and radiation or electrical shock.
• Chemical agents encompass poisons (e.g., arsenic, cyanide), hypertonic solutions (glucose/salts), environmental pollutants, alcohol, and narcotic drugs.
• Infectious agents include viruses, bacteria, fungi, and parasites.
• Immunologic reactions involve the immune system causing cell injury, such as in autoimmune diseases and anaphylactic reactions.
• Genetic abnormalities can lead to pathologies, evident in conditions like Down syndrome or sickle cell anemia.
• Nutritional imbalances include protein-calorie deficiencies, vitamin insufficiencies, and excessive lipids leading to atherosclerosis.
• Aging results in cellular senescence, impacting replication and repair capabilities.

Types of Cell Death

• Necrosis is uncontrolled cell death due to factors like hypoxia, physical agents, or toxic substances.
  • Liquefactive necrosis occurs in the brain, forming cavities due to tissue liquefaction.
  • Caseous necrosis characterizes tuberculosis infections, presenting as cheesy, necrotic tissue.
  • Gangrenous necrosis involves large-scale tissue death due to ischemia or infection, often leading to putrefaction and foul odors.

Apoptosis

• Apoptosis is programmed cell death, crucial for normal development and maintenance of tissue homeostasis.
• Genes involved include pro-apoptotic genes (e.g., bax) that stimulate apoptosis and anti-apoptotic genes (e.g., bcl) that inhibit it.

Physiologic and Pathologic Conditions of Apoptosis

• Physiologic apoptosis occurs during embryogenesis, hormone-driven tissue involution, and elimination of unnecessary immune cells.
• Pathologic apoptosis can be triggered by cytotoxic T lymphocytes, DNA damage, accumulation of misfolded proteins, and viral infections leading to cell loss.

Hypertrophy and Hyperplasia

• Hypertrophy is an increase in cell size due to increased functional demand or stimuli.
• Hyperplasia involves an increase in cell number, contributing to tissue or organ enlargement.
  • Physiologic hyperplasia includes hormonal (e.g., breast tissue during pregnancy) and compensatory types (e.g., liver regeneration post-resection).
  • Pathologic hyperplasia denotes excessive proliferation, like endometrial hyperplasia due to estrogen imbalance.

Calcification Types

• Dystrophic calcification involves calcium deposits in dead or dying tissue without abnormal calcium metabolism; often seen in necrotic tissues and certain tumors.
• Metastatic calcification occurs in living tissues due to hypercalcemia, linked to conditions such as primary or metastatic bone tumors, renal failure, and increased parathyroid hormone secretion.

Key Terms

• Psammoma Bodies are dystrophic calcified deposits found in certain malignant tumors, indicating a specific type of calcification associated with cancerous growths.

This quiz covers the cellular responses to stress and noxious stimuli, focusing on cell injury, cell death, and adaptations. Topics such as necrosis, apoptosis, and pathological calcification are explored to understand how cells respond to damaging conditions. Test your knowledge on these critical aspects of cellular biology.