190 NETERINARY PATHOLOGY. 



accustomed to the extra work gradually- An excessive amount 

 of work, assumed at once, J^v any structure will produce atrophy 

 or degeneration. Cardiac hypertroph_y is invariably functional 

 as it usualh' is the result of valvular defects. Hypertrophy of 

 the involuntary muscle anterior to a stricture is also functional 

 as it results from increased muscular action to force the contents 

 of the intestine past the stricture. A'oluntary muscular hyper- 

 troph)' is also functional. 



Some unknown cause is active in the production of certain 

 hypertrophic conditions. This unknown cause is probably an 

 internal secretion, at least this would appear to be the cause of 

 hypertropliy of the mammae and uterus in pregnant animals. 

 That certain internal secretions are re(|uired to sustain the nor- 

 mal balance in the growth of tissues is evident in disease of the 

 pituitary budv which frequently results in excessive develop- 

 ment (if certain parts (acromegaly). 



By diminishing tlie external pressure, e.xperimentally, some 

 parts ha\"e Iicen noted to l^ecome h\'pertrophic. This is because 

 of arterial hyperemia produced liy diminished pressure. 



Appearance. 



Macroscdf^icdlly. liypcrtrophied organs or parts are larger 

 and hea^'ier tlian normal and may l)e regular or irregular in 

 shape. The general appearance of hypertrophied parts other 

 than size is not usually sufficiently distinct to differentiate them 

 from normal. 



M icrosc'd/^ic. — Renal compen^ator\- hypertrophy is charac- 

 terized l)y increased length and size of the uriniferous tubules. 

 Hypertrophy nf muscular tissue is characterized by increase in 

 the size of muscle cells. In general hypertrophied organs or 

 parts contain an excess of parenchymatous tissue. 



Effects. — 1^he effect of liypertrophy \-aries according to the 

 tissue affected. There is usually an increased functional capac- 

 ity in an hypertrophied structure. The heart musculature may 

 become hypertrophied to such an extent that its furce ruptures 

 some important blood vessel and causes death. Increased func- 

 tion of h\']5ertrophied 'suprarenal bfidies tends to increase 

 blood pressure by tlie ]u-(iduction and elimination of large quan- 

 tities of adrenaline which causes constriction of arteries and 

 cardiac dilation or rupture. 



