Cell Injury

Components:
- Surrounded by a cell membrane (phospholipids and proteins)
- Contains a nucleus which regulates cellular activity.
- Cytoplasm: jelly-like substance housing organelles.
Organelles Include:
- Mitochondria, Golgi apparatus, ribosomes, lysosomes, centrioles, etc.

Normal Cell Function: Cells maintain a steady state through homeostasis.
They control their immediate environment to stay within physiological parameters.

Body organization: Atoms → Molecules → Cells → Tissues → Organs → Organ Systems.
Extracellular components like the extracellular matrix and fluid are also important.
Changes in homeostasis due to injury can lead to disease.

Derived from French: "Dis + Ease" meaning lack of ease or discomfort.
Disease is any departure from a normal state of health.
It disrupts normal physiological functions of parts or organs, leading to symptoms.

Genetic: Abnormalities in DNA sequences, can affect acquired diseases.
Acquired: Develop post-birth due to environmental or external factors.
Congenital: Present from birth, may develop from either genetic or environmental factors.

Ischemia: Lack of blood flow causing hypoxia/anoxia, leading to cell injury and potentially infarction.
- Example: Cardiac ischemia can lead to myocardial infarction (heart attack).
Physical Agents:
- Temperature extremes: Cause burns or frostbite.
- Radiation: Can damage tissues (e.g., sunburn).
- Electric Current: High voltage can cause lethal injuries.
- Mechanical Trauma: Wounds or organ rupture.
Chemical Agents: Disruption of cellular pathways through toxic compounds.
- Example: Cyanide inhibits cytochrome oxidase leading to cellular asphyxiation.
Infectious Agents: Pathogens like viruses, bacteria, fungi causing cell damage.
Nutritional Disorders: Imbalances leading to obesity or deficiencies (e.g., anaemia from iron deficiency).
Immunological Disorders: Autoimmune diseases where the body attacks its own tissues (e.g., psoriasis).
Genetic Disorders: Conditions arising from genetic mutations, e.g., sickle cell disease.
Congenital Disorders: Conditions present at birth due to developmental issues.

Severity of injury determines whether cells adapt or die.
Cellular Adaptation: Cells can adapt non-lethally under stress.
- Examples include hypertrophy (increased cell size), hyperplasia (increased cell number), atrophy (decreased size), metaplasia (type change), and dysplasia (disordered growth).
Cell Death: Can be irreversible following severe injury or stress.

Hypertrophy: Increase in cell size; seen in muscles experiencing increased demand.
- Example: Heart enlargement due to increased thyroid hormone in feline cardiomyopathy.
Hyperplasia: Increase in cell number often in response to a stimulus.
- Types include physiological (e.g., during pregnancy) and pathological (e.g., psoriasis).
Atrophy: Decrease in cell size due to decreased load or nutrition.
- Can be physiological (e.g., post-childbirth uterus) or pathological (e.g., muscle atrophy from disuse).
Metaplasia: One adult cell type replaced by another better suited to tolerate change (e.g., respiratory cells adapting to smoke exposure).
- This can lead to loss of normal function and predispose to cancer.
Dysplasia: Abnormal cellular growth and arrangement; considered a precursor to cancer.
- Often found in conditions like cervical intraepithelial neoplasia (CIN).

Causes include ischemia, physical agents, infectious agents, chemical agents, nutritional disorders, immunological disorders, genetic and congenital disorders.