Hypertrophy vs Hyperplasia
Hyperplasia and hypertrophy are two terms used in pathology to explain growth abnormalities in living tissues. Usually under normal physiological stimulation, tissue display normal orderly growth patterns. Under excessive or abnormal stimulations, the tissues grow out of the ordinary. Being two different pathological entities, there are many differences between hyperplasia and hypertrophy, which will be clarified in this article, in detail by defining hyperplasia and hypertrophy and their types, and highlighting their mechanism, and causes.
Hyperplasia is an increase in the size of tissue as a result of increased number of component cells. It is the principal mechanism accounting for increased size in tissues composed of labile and stable cells. Hyperplasia results when the component cells of a tissue are stimulated to undergo mitotic division, thereby increasing the number of cells. Physiological hyperplasia is a result of increased stimulation. When the stimulation is removed, the tissues return to normal. Pathological hyperplasia is also due to increased stimulation of the cells of tissues. However, in pathological hyperplasia, tissues do not return to normal once the stimuli are removed. Endometrial hyperplasia is an important result of increased estrogen stimulation, particularly when the estrogen is not opposed by progesterone. This is the case in peri-menopausal period. This causes excessive uterine bleeding. The presence of excessive trophic hormones (hormones that trigger a target organ to grow and function) causes hyperplasia of the target organs. Excessive secretion of Adrenocorticotrophic hormone causes bilateral adrenal hyperplasia. Hyperplastic target organs frequently show increased function. In case of adrenal glands, there is excessive secretion of cortisol. Thyroid hyperplasia results from increased Thyroid Stimulating Hormone (TSH) from the anterior pituitary or due to the action of autoantibodies that are able to bind to TSH receptors on the thyroid cell membrane. Hyperplasia of the prostate gland is common in elderly males due to hyperplasia of both stromal and glandular elements. The exact cause is not known, but dropping androgen levels may be responsible.
Hypertrophy is an increase in the size of a tissue due to increased size of individual cells. It occurs in tissues made up of permanent cells, in which a demand for increased metabolic activity cannot be met through cell manipulation. (Read more about Permanent Tissue) Hypertrophy results from increased amounts of cytoplasm and cytoplasmic organelles in cells. In secretory cells, the secretary system – including the endoplasmic reticulum, ribosomes, and the Golgi zone – become prominent. In contractile cells like muscle fibers, there is an increase in the size of myofibrils. Hypertrophy is due to increased demand. In physiological hypertrophy, when the demand is removed, the tissues return to normal overtime. Pathological hypertrophy is also due to increased demand. However, in pathological hypertrophy, tissues do not return to normal when the demand is removed. Myocardial hypertrophy, if it occurs without a recognizable cause, is considered as an example of pathological hypertrophy. Such hypertrophy is frequently associated with abnormal cardiac function.
What is the difference between Hyperplasia and Hypertrophy?
• Hypertrophy occurs in permanent cells while hyperplasia occurs in labile or stable cells. Hypertrophy is due to increased demand while mostly hyperplasia is due to excessive cell stimulation.
• Both hypertrophy and hyperplasia can occur together as a result of increased demand.
• Hypertrophy features enlargement of stromal and cellular components by increasing their size without multiplying while hyperplasia increases tissue size by cell division.