Cellular Injury and Adaptation

Pathology -Morphology : gross and microscopic changes of cell and tissue -Use ancillary techniques as : Histochemical,immunohistochemical, molecular and cytogenetics - This will result in signs & symptoms At the end : the pathologist will give a diagnosis and guide therapy. Pathology is the discipline that bridges clinical practice and basic science

(stress stimuli) Cells are constantly adjusting their structure and function to accommodate changes in their environment (stress stimuli) ADAPTATION Achieving a new steady state and preserving viability i.e. ADAPTATION if the cell adaptive capability is exceeded cell injury develops The Cell and the Environment

Stimuli CellAdaptation Cell Injury Reversible Irreversible (cell death) apoptosisnecrosis

Causes of Cell Injury 1. Hypoxia: 1. Hypoxia: (Oxygen deficiency) Mainly due to: most common  ischemia (impaired blood supply) most common  inadequate oxygenation of blood (cardio-respiratory failure)  loss of oxygen carrying capacity (anaemia)  Carbon monoxide poisoning 2. Physical Agents  Trauma, radiation, extremes of temperatures, electric shock 3. Chemicals and Drugs  Wide variety 4. Microbiologic Agents  Viruses, worms, bacteria ….. 5. Immunologic Reactions  Allergic reactions, autoimmune diseases 6. Genetic Defects  Obvious congenital malformations (Down syndrome)  Subtle single amino acid substitution (hemoglobin S of sickle cell anemia) 7. Nutritional Imbalances  Deficiency of nutrients/ or excess 8. Aging

There are 4 main forms of Adaptation Atrophy: Atrophy: decrease in size decrease in size or number of cells leading to reduction in tissue mass Hypertrophy: Hypertrophy: increase in size increase in size of cells leading to increase in size of organ Hyperplasia: Hyperplasia: increase in number increase in number of cells leading to increase size of organ Metaplasia: Metaplasia: reversible change reversible change in which one adult tissue type is replaced by another

Cellular Adaptation to Injury Physiologic Responses to normal processes Pathologic Allows cells to modulate environment and hopefully escape injury Cellular adaptive responses can occur at any of these Steps: Receptor binding, signal transduction, protein transcription, translation, export

Atrophy Definition: Definition: Shrinkage in the size of a cell by loss of cell substance cells are NOT dead Diminished cell function but cells are NOT dead Organ Atrophy Results when a substantial number of cells are involved by: Cell atrophy (cells living)

Atrophy Causes Causes Decreased workload Loss of innervations Diminished blood supply Inadequate nutrition Loss of endocrine stimulation Aging

Atrophy Biochemical Mechanisms Biochemical Mechanisms Decreased protein synthesis Increased protein catabolism (degradation)  Or/ Both Morphology Decreased cell size Atrophy represents a reduction in the structural components of the cells contain fewer mitochondria and myofilaments and a lesser amount of endoplasmic reticulum Increased autophagic vacuoles Increased residual bodies (lipofuscin)

Normal Atrophy

Kidneys, left side normal size right side atrophy