Cell Death and Necrosis Mechanisms
Overview of Cellular Responses to Stress
Focus on cellular responses to stress, leading to adaptations or injury.
Stress and Cell Response
Stress can lead to growth adaptations:
Hyperplasia: Increase in the number of cells.
Hypertrophy: Increase in cell size.
Reducing stress can lead to atrophy: Decrease in cell size or function.
A change in stress level can lead to anaplasia: Reversion to a more primitive cell type.
Cellular Injury and Death
Severe stress results in injury:
Initial stage is known as reversible cellular injury.
Persistent injury leads to irreversible injury, also termed cell death.
Hallmarks of Cell Death
Morphologic hallmark of cell death:
Loss of nucleus (if nuclei are absent, tissue is considered dead).
Stages of nuclear loss:
Pyknosis: Shrinking of the nucleus.
Karyorrhexis: Fragmentation of the nucleus.
Karyolysis: Dissolution of the nucleus into basic components.
Mechanisms of Cell Death
Two primary mechanisms:
Necrosis
Described as murder; involves external pathological processes leading to large-scale tissue destruction.
Always leads to acute inflammation.
Necrosis is not a physiological process; it indicates disease or serious injury.
Types of necrosis, often examined:
Coagulative necrosis:
Tissue remains firm with retained architecture despite cell death.
Hallmark characteristics: Lost nuclei, firm necrotic tissue.
Typically occurs in ischemic infarction (like myocardial infarction).
Wedge-shaped, pale areas of infarction based on blood supply patterns.
Liquefaction necrosis:
Necrotic tissue becomes liquefied and may be seen in diabetic patients.
Often associated with infections leading to pus formation.
Caseous necrosis:
A specific type of liquefaction necrosis associated with tuberculosis or fungal infections, leading to cottage cheese-like appearance.
Fat necrosis:
Involves necrosis of adipose tissue, appearing chalky white due to fat release.
Common in acute pancreatitis due to fat cell breakdown.
Trauma to breast can also lead to fat necrosis, potentially presenting as a mass with giant cell reactivity.
Subconfication: Calcium binding with damaged fatty acids, also relates to the soap-making process and is a form of dystrophic calcification.
Summary Points About Necrosis
Dystrophic calcification: Calcium deposits in necrotic or dying tissues despite normal serum levels.
Metastatic calcification: Involves abnormal calcium metabolism, leading to deposits irrespective of local tissue necrosis.
Important to note that examinations may inquire about both the characteristics of necrosis types and their physiological implications.