Cellular Injury II: Classification

Hypoxic injury results from reduced oxygen delivery to tissues, most often due to inadequate blood supply from arterial obstruction. For example, a coronary artery thrombosis restricts blood flow to heart muscle, causing myocardial infarction. This oxygen deprivation prevents cells from maintaining normal metabolic functions and homeostasis.

Chemical injury occurs when toxic substances like mercury, strong acids, or drugs damage cells directly or indirectly through harmful metabolites. Acetaminophen overdose exemplifies indirect chemical injury, where the drug's metabolites cause cellular damage. These agents disrupt normal cellular processes and structural integrity.

Key mechanisms include ATP depletion from mitochondrial dysfunction, oxidative stress from reactive oxygen species accumulation, calcium influx activating destructive enzymes, and membrane damage causing cellular content leakage. Mitochondrial damage reduces ATP production and may trigger cell death pathways like apoptosis and autophagy. Protein misfolding and DNA damage impair cellular repair mechanisms.

Infectious injury is caused by bacteria, viruses, fungi, or parasites that damage cells directly or trigger an inflammatory response during the immune system's reaction. Pathogens can destroy cellular structures or activate immune mechanisms that harm infected cells. This dual mechanism makes infectious injury particularly damaging to tissue.

Immunologic injury results from abnormal immune responses, including allergies and autoimmune diseases like lupus. The immune system mistakenly attacks the body's own cells, causing structural and functional damage. This type of injury reflects a fundamental failure of immune tolerance and self-recognition mechanisms.

Physical injury includes trauma, extreme temperatures, electrical shock, and radiation, all of which directly disrupt cellular structure and function. These agents mechanically damage or kill cells through direct physical force or energy transfer. Physical injuries can range from localized cellular damage to widespread tissue destruction.

Genetic and metabolic causes such as inherited mutations or conditions like diabetes impair normal cellular function. These conditions disrupt cellular processes at fundamental levels, preventing cells from maintaining homeostasis. Over time, such disruptions lead to structural and functional cellular changes affecting tissue health.