CHAPTER VIII. 

 RETROGRESSIVE TISSUE CHANGES. 



DEFINITION. 

 ETIOLOGY. 



Variations m nutrition. 



Cheinic poisons. 



Chemic reaction of tissue. 



Variations of temperature. 



Variations of function. 

 VARIETIES. 



Atrophy. 



Degeneration. 



Infiltration. 



Pigmentation. 



Physiologic cell growth and function are dependent upon nor- 

 mal metabolism. Retrogressive processes are those conditions in 

 which normal cell growth and function are diminished or sus- 

 pended. Retrogressive tissue changes are caused primarily by 

 abnormal cell metabolism or abnormal functioning, and are 

 accompanied by structural or chemic alteration of the cell proto- 

 plasm or diminution in the size of the cells. 



Metabolic disturbances may be caused by the following: 

 Diminished nidritiz'c supply caused by (a) occlusion or di- 

 minution of the calibre of nutrient vessels; (b) insufficient 

 supply of food to the animal; (c) incomplete or lack of digestion 

 of the ingested food; (d) failure of absorption of digested food; 

 (e) inability of the cells to utilize digested food that has been 

 carried to them. Nutrition may be supplied in excess of the 

 normal requirements, thus disturbing the metabolic equilibrium. 

 Excess nutrients may be stored within the cells or thev may be 

 converted into energv by oxidation. In the former the stored 

 food is a mechanical hindrance to cell action and in the latter 

 the cell is overworked in converting the food into energy. With- 

 holding of nutrient substances from cells produces destructive 

 metabolism and ultimately cell death. 



Chemical substances, i. e., poisons exert their action on cells 

 by combining with some of the protoplasmic constituents or by 

 accelerating, inhibiting or suspending the action of the cell 

 enzyms, thus interfering with metabolism. 



Chemic reaction of a tissue influences the action of cell 



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