Atrophy

DEFINITIONdecrease in size and weight of a tissue/organ CAUSESDecreased hormonal stimulation of hormone-responsive tissueHypopituitarism causing atrophy of target organs-thyroid, adrenal cortexPhysiological atrophy of breast and uterus following menopause, when estrogen stimulation is diminished

Decreased workload/disuseSkeletal muscle in plaster cast

Dennervation of muscleSkeletal muscle atrophy following lower motor neuron loss in Amyotrophic lateral sclerosis

Decreased blood supplyCerebral atrophy due to atherosclerosis of CA

Decreased nutritionCalorie deprivation in marasmus/kwarshiokorAs a result of utilization of skeletal muscle proteins as source of energy after other reserves have been depleted.

Increased pressure/compressionAtrophy of renal cortex and medulla in hydronephrosis (increased luminal pressure of backed up urine compresses vessels in medulla and cortex)Compression atrophy of exocrine glands in cystic fibrosis (thick pancreatic duct secretions occlude duct lumens, causing increased luminal back pressure, resulting in atrophy and damage)Enlarging benign tumor can cause atrophy of surrounding uninvolved tissues.

Pressure exerted causes the blood supply to compromise, resulting in ischemic changes??

MECHANISMS

SHRINKAGE OF CELLS (by reduction in cytosol and number of organelles through Autophagy[formation of autophagic vacuoles-fusion with primary lysosomes=autophagolysosomes->enzymatic degradation]..[lipid peroxidation of cell membranes-undigested stored as residual bodies, e.g. Lipofuscin, brown tissue discoloration/brown atrophy, normal age-related finding)LOSS OF CELLS by PCD/apoptosisPROTEIN CATABOLISM-decreased protein synthesis (wasting syndrome?/catabolic state?) and increased protein degradation (ubiquitin-proteasome pathway)