Atrophy Flashcards
Atrophy
Condition where the decrease in the size of normally developed cells, tissues, or organs occurs
- decrease in cell number OR cell size
- is an adaptation to an altered cell environment
- can be physiologic or pathologic
What are the 2 ways an organ can shrink?
- cell deletion (apoptosis)
- cell shrinkage
Cell deletion
Most specialized cells are removed first (gland cells before ducts), leaving stroma –> fibrotic appearance
Cell shrinkage
Each cell must trim down excess
- flesh and bones of cells are proteins
- organelles of atrophied cells are reduced, mitochondria are smaller, lack secretory granules
What must occur for a cell to shrink?
Proteolysis
- autophagy
- ubiquitin/proteasome pathways
Autophagy
Survival mechanism during ischemia or a response to hormones
- cells consume damaged organelles and recycle proteins/carbs
- protective mechanism to avoid cell death
Autophagy mechanism
Autophagosome is produced –> contains dysfunctional organelles –> residual bodies –> may be retained (lipofuscin)
What are the 3 types of protein removal systems?
- ubiquitin proteasome
- chaperone mediated autophagy
- macroautophagy
Ubiquitin proteasome pathway
Anything that needs to go is tagged with ubiquitin and the proteasome is the “trash can”
- usually for small protein
Chaperone mediated autophagy
Lysosomal digestion for larger proteins
Macroautophagy
Taking cellular material and putting it in a lysosome for ingestion
- ULK1 complex that makes isolation membrane out of the golgi system
What are the 10 possible etiologies for atrophy?
- decreased function
- physiologic
- cachexia
- impaired bloodflow
- pressure
- duct occlusion
- hormones
- age
- denervation
- inflammation/toxins
Decreased use/function
Inactivity or limited movement –> promotes protein catabolism (as does muscle trauma)
Physiologic
Programmed cell death of certain tissues
- thymus
- involution of uterus and mammary glands after parturition and lactation
Cachexia
Starvation, chronic infections, cancer, uremia, burns, sepsis, fasting
Diffuse muscle wasting
Catabolism via the ubiquitin-proteasome pathway
Serous atrophy of fat
Utilization
Moderate caloric restriction, can ______ lifespan
Increase
- occurs in: mammals, spiders, paramecia, dwarf flies
- undernutrition, NOT malnutrition!
Impaired bloodflow
Chronic ischemia –> prolonged partial inadequacy of blood
Pressure
Growing tumors cause local pressure –> due to reduced bloodflow
- constant local pressure stimulates osteoclasts –> bone loss
- meningioma, retina from glaucoma
Duct occlusion
- exocrine glands: pancreas, salivary glands lose secretory cells by apoptosis
- kidney: occlusion of ureter leads to hydronephrosis
Hormones/endocrine
- natural sexual cycles: ovary and testis
- iatrogenic supply of hormone –> the best way to atrophy an endocrine gland is to supply it with its own hormone
- could induce atrophy with corticosteroids
Age
Reproductive organs –> muscles –> bone –> nervous system
Denervation
- motor nerve: marked effects on skeletal muscle
- sensory nerve (humans): skin atrophies, nails become brittle
- sympathetic: metabolic effects on arteries, salivary gland atrophy, perirenal fat metaplasia (brown fat)
Inflammation
Cytokines cause atrophy in organs
- rhinitis, intestinal viruses (villus atrophy)
