Page 585 - The Veterinary Laboratory and Field Manual 3rd Edition

522 Samuel Sharpe

on a tissue or organ, for instance hypertrophy of
nephrons in one kidney if the other kidney has
been removed or damaged or myocardial hyper-
trophy in response to exercise.
Not all hypertrophic change is beneficial how-
ever. Dilated cardiomyopathy in small animals is
an idiopathic condition which results in progres-
sive cardiac myocyte dysfunction and loss. In the
initial stages of the disease cardiac function is
maintained by remaining cardiac myocytes. After
time, however, the increased energy demands
of hypertrophic myocytes and loss of efficiency
results in impaired myocardial function and con-
gestive heart failure.
Hyperplasia can be further subdivided into
Figure A2.8 Liver, sheep. Necrosis: there are physiological or pathological change. Physiological
multifocal, slightly sunken areas of tan discol- hyperplasia can occur as a result of hormonal stim-
ouration throughout the liver, visible from the ulation in response to changing demands such as
capsular surface. This is a characteristic appear- mammary gland hyperplasia during lactation, or
ance of hepatocellular necrosis in this case as the be compensatory such as in the liver if part of
result of Fusobacterium necrophorum infection. the organ is removed or irrevocably damaged the
F. necrophorum usually reaches the liver via the remaining hepatocytes will divide to restore func-
portal circulation from the rumen and is a com- tional mass. Examples of pathological hyperplasia
mon sequelae to acute rumenitis. Necrosis can be include benign prostatic hyperplasia in entire
differentiated from degenerative (glycogenosis or
lipidosis) changes which can have a similar homog-
enous tan appearance by the fact lesions in this
case are sunken consistent with tissue loss. See
also Plate 48.
A2.8 disorders of growth

Hyperplasia/hypertrophy

Hypertrophy is defined as an increase in size
of an organ or tissue caused by an increase in
size of component cells. In contrast hyperpla-
sia is defined as an increase in size of an organ Figure A2.9 Urinary tract, dog. Benign prostatic
caused by an increase in number of component hyperplasia. Note the enlarged prostate (closed
cells. In both cases the change is reversible and arrow) surrounding the proximal urethra at the neck
the organ will revert to normal size if the stimu- of the urinary bladder (open arrow). The smooth
lus is removed. In either case the lesions noted outer contour and symmetrical appearance of the
grossly will be an increase in size of a tissue or right and left lobes of the gland are consistent with
organ in part or whole. Hypertrophy is usually hyperplasia. See also Online figure 6. Photo: cour-
physiological in response to increased demands tesy of Dr J. Davies, University of Calgary, Canada.

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