General Pathology: Cell Injury and Adaptation
Understanding how cells respond to stress and injury is fundamental to grasping disease processes. This module covers the initial cellular responses, from reversible adaptations to irreversible injury and cell death.
Mechanisms of Cell Injury
Cell injury can be triggered by a variety of insults, including oxygen deprivation (ischemia), chemical agents, infectious agents, immunologic reactions, genetic defects, and physical agents. The response of the cell depends on the nature of the insult, its duration, and its severity, as well as the state of the cell.
Key Biochemical Mechanisms of Injury
Several critical cellular components are targets of injury. Understanding these mechanisms is crucial for comprehending how different insults lead to cellular dysfunction.
Apoptosis and Necrosis.
Cellular Adaptations
Cells can adapt to changes in their environment or to increased functional demands by altering their size, number, phenotype, or function. These adaptations are generally reversible.
| Adaptation | Description | Example |
|---|---|---|
| Hypertrophy | Increase in cell size | Enlargement of cardiac myocytes in response to valvular stenosis |
| Hyperplasia | Increase in cell number | Enlargement of the uterus during pregnancy |
| Atrophy | Decrease in cell size and number | Disuse atrophy of skeletal muscle after immobilization |
| Metaplasia | Reversible change in which one adult cell type is replaced by another adult cell type | Squamous metaplasia in the respiratory tract of smokers |
Types of Cell Death
When cellular injury is too severe to be reversed, cells undergo programmed cell death (apoptosis) or uncontrolled cell death (necrosis).
Necrosis is a form of cell death characterized by the loss of membrane integrity, enzymatic digestion of cellular components, and inflammation. It typically occurs in response to irreversible injury. Morphologically, it involves eosinophilia of the cytoplasm, pyknosis (nuclear shrinkage), karyorrhexis (nuclear fragmentation), and karyolysis (dissolution of the nucleus). Different patterns of necrosis exist, such as coagulative, liquefactive, and caseous necrosis, each reflecting the underlying cause and tissue type.
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Remember: Necrosis is always pathological, while apoptosis can be physiological or pathological.
Summary and Key Takeaways
Cell injury is a spectrum from reversible adaptation to irreversible death. Key mechanisms involve mitochondrial dysfunction, membrane damage, and oxidative stress. Adaptations like hypertrophy and hyperplasia allow cells to cope with stress, while necrosis and apoptosis represent distinct forms of cell death with different morphological and functional consequences.
Learning Resources
The foundational chapter from Pathoma, a highly recommended resource for USMLE preparation, covering cell injury, adaptation, and death in detail.
The official textbook chapter from Robbins, providing comprehensive and authoritative information on the topic.
A clear and concise video explanation of cell injury, adaptation, and death, ideal for visual learners.
An in-depth lecture covering the core concepts of cell injury, adaptation, and death with detailed explanations and diagrams.
A foundational video from Khan Academy that introduces the basic principles of cell injury and adaptation.
Dr. Ryan's comprehensive video series for USMLE preparation, including detailed lectures on pathology topics.
A detailed overview of apoptosis, its mechanisms, and its role in biology and disease.
An in-depth explanation of necrosis, its types, causes, and pathological significance.
A chapter from a medical biochemistry textbook that delves into the mechanisms and consequences of oxidative stress.
A concise and well-organized summary of cell injury, adaptation, and death, often used as a quick reference for medical professionals.