Atrophy
An adaptive response characterized by decreased protein synthesis and increased protein degradation.
- Cells decrease in size
- Degradation of proteins using:
- Lysosomes
- Ubiquitin-proteasome pathway
- Autophagy
- "Self-eating"
- Natural, regulated mechanism of the cell that disassembles unnecessary or dysfunctional components
- Elimination of intracellular substances
- Membrane-bound vacuoles containing mitochondria, ER, complex protein fragments and undegradable substances
- Undegradable substances accumulate, and with time, can be seen as pigments (lipofuscin and hemosiderin)
- Plays a role in many physiological and pathological processes
- Occurs due to:
- Decreased workload (inactivity)
- Reduced blood supply or innervation
- Nutritional defect (cachexia)
- Loss of hormonal stimulation
- Aging
- Pressure/tension
- Examples:
- Cerebral atrophy (due to aging or disease)
- Muscle atrophy (due to prolonged bed rest)
Involution
A general term for describing the shrinking of an organ.
- Characterized by both atrophy and programmed cell death (apoptosis)
- Notable examples:
- Uterus after pregnancy
- Thymus gland after