GENERAL PATHOLOGIC CHANGES 237 



HYPERTROPHY 



Hypertrophy is the enlargement of a part of the body. The 

 increased size may be due either to physiologic or pathologic 

 causes. In either case the part or organ involved takes on in- 

 creased functional activity. An example is seen in the case of a 

 giant, where the condition is general. Physiologic hypertrophy 

 occurs because 3n increased demand is made upon the organ; 

 for example, the muscles of a gymnast or the biceps of the black- 

 smith. The heart shows the effects, especially in horses used 

 for fast or very heavy work. In these the heart is always much 

 larger than in animals not placed under such strain. Com- 

 parison of the heart from a dog with one from a sheep or pig of the 

 same weight will reveal a decided difference, due to their mode of 

 life. If one kidney becomes diseased and cannot function, the 

 opposite is increased to double the usual size (compensatory 

 hypertrophy); but there is usually no indication of kidney 

 disease observable during life. 



ATROPHY 



Atrophy is a wasting away or diminution in the bulk of one 

 or more of the component parts of an organ, accompanied by a 

 diminution in function. It is the reverse of hypertrophy. 

 Examples of atrophy are seen in the thymus gland of young 

 animals, the uterus of old mares, and "sweeny" following injury 

 to the shoulder muscles. A peculiar form of this change is 

 called "senile atrophy," noticeable in the sexual glands of the 

 aged and prematurely aged. Brittleness of bones in the old is 

 another example. Causes of atrophy include all those factors 

 which interfere with the nutrition and activity of an organ. 

 In starvation the fat of the body disappears and the organs 

 atrophy, so .that the animal may lose more than hah in weight. 

 Deficient nutrition, due to interference with the normal blood 

 supply, may occasion atrophy. This form is seen when the chief 

 artery to a part is ligated. Constant pressure inhibits growth 

 and leads to a decrease in size, as may be seen in the deep groove 

 left across the nose of a horse tied for a long time by a halter 

 with a tight nose-band. In old horses the liver is smaller than 

 in young animals, due to long-continued pressure from other 

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