Cellular Morphological Response

Study Notes

Changes in cell shape due to various conditions.
Response to stress varies between reversible injury, adaptation, and cell death.

Metabolic Disturbances cause abnormal material build-up inside cells.
Triglycerides: Accumulates in cells, e.g., fatty liver.
Cholesterol: Accumulates in macrophages and smooth muscle cells, contributing to atherosclerosis.
Proteins: Immunoglobulins accumulate in plasma cells during immune responses.
Glycogen: Accumulates in liver and muscle in glycogen storage diseases.
Pigments:
- From outside the body or inside:
  - Carbon (anthracosis): Black pigment that accumulates in the lungs.
  - Lipofuscin (aging pigment): Yellow-brown pigment accumulating in aging cells.
  - Iron (in hemosiderosis): Accumulates in various tissues due to iron overload.
- From inside the body: Forms pigments like bilirubin (in jaundice).

Morphologic and functional changes in cells due to a long lifespan.
Caused by: Cellular damage accumulation, reduced DNA repair, reduced division capacity, altered protein homeostasis, and effects of high caloric intake.
Morphological Responses: Abnormal nuclei, mitochondria, Golgi apparatus; decreased endoplasmic reticulum and ribosomes; accumulation of lipofuscin.
Examples:
- Lipofuscin in neurons.
- Lipofuscin in cardiac muscle.
Autophagy is the main mechanism of cellular aging.
- Cellular organelles are engulfed by cytoplasmic vacuoles that fuse with lysosomes to digest the engulfed organelle.
- Autophagy also occurs in cancers.

Hypertrophy: Increased cell size due to increased workload or growth.
- Example: Hypertrophy of smooth muscle cells in the uterus during pregnancy.
**Hyperplasia:**Increased cell number due to hormonal or growth factor stimulation.
- Example: Hormonal hyperplasia of the female breast during puberty.
Atrophy: Decreased cell size due to reduced nutrient supply, blood flow, or disuse.
- Mechanism: Reduced protein synthesis and increased protein breakdown.
- Example: Senile brain atrophy.
Metaplasia: Replacement of one differentiated cell type by another of the same category in response to chronic irritation.
- Purpose: Cells become better equipped to handle the stress.
- Example: Squamous metaplasia of respiratory epithelium in smokers.

Includes:
- Cellular swelling: Intracellular water accumulation, e.g., kidney tubules lining epithelium.
- Fatty change: Intracellular fat accumulation, e.g., hepatocytes.
Morphology:
- Cell swelling.
- Cell membrane blebs.
- Mitochondrial swelling.
- Swelling of the endoplasmic reticulum.
Cells retain their shape and can recover after injury.

A- Necrosis: Death of a group of cells or tissues.
- Morphology:
  - Cells become more eosinophilic.
  - Nuclear dissolution.
  - Breakdown of cell membranes, forming myelin figures.
  - Digestion of cellular contents.
  - Surrounding inflammation.
B- Apoptosis
- Programmed cell death to remove unwanted or damaged cells.
- Mechanism: Activation of caspases, fragmenting cells into apoptotic bodies, and phagocytosis of fragments.
- Pathways:
  - Intrinsic pathway: Triggered by DNA damage or cellular stress.
  - Extrinsic pathway: Triggered by death receptors on the cell surface.