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Enlargement of tissue due to cell proliferation
Medical condition
Hyperplasia
Whereas
hypertrophy stems from an increase in
cell size, hyperplasia results from an increase in cell number.
Hyperplasia (from
ancient Greek ὑπέρ huper 'over' + πλάσις plasis 'formation'), or hypergenesis, is an enlargement of an organ or tissue caused by an increase in the amount of
organic tissue that results from
cell proliferation.[4] It may lead to the
gross enlargement of an organ, and the term is sometimes confused with benign
neoplasia or
benign tumor.[5]
Hyperplasia is a common preneoplastic response to stimulus.[6] Microscopically, cells resemble normal cells but are increased in numbers. Sometimes cells may also be increased in size (
hypertrophy).[7] Hyperplasia is different from hypertrophy in that the
adaptive cell change in hypertrophy is an increase in the
size of cells, whereas hyperplasia involves an increase in the number of cells.[8]
-plasia and -trophy
Anaplasia (structural differentiation loss within a cell or group of cells).
Hyperplasia may be due to any number of causes, including proliferation of basal layer of epidermis to compensate skin loss,
chronic inflammatory response,
hormonal dysfunctions, or
compensation for
damage or
disease elsewhere.[9] Hyperplasia may be harmless and occur on a particular tissue. An example of a normal hyperplastic response would be the growth and multiplication of milk-secreting
glandular cells in the
breast as a response to
pregnancy, thus preparing for future
breast feeding.[10]
Perhaps the most interesting and potent[editorializing] effect
insulin-like growth factor 1 (IGF) has on the human body is its ability to cause hyperplasia, which is an actual splitting of cells.[11] By contrast,
hypertrophy is what occurs, for example, to skeletal muscle cells during
weight training and is simply an increase in the size of the cells.[12] With IGF use, one is able to cause hyperplasia which actually increases the number of muscle cells present in the tissue.[13] Weight training enables these new cells to mature in size and strength. It is theorized that hyperplasia may also be induced through specific power output training for athletic performance, thus increasing the number of muscle fibers instead of increasing the size of a single fiber.[14]
Mechanism
Hyperplasia is considered to be a
physiological (normal) response to a specific stimulus, and the cells of a hyperplastic growth remain subject to normal
regulatory control mechanisms.[5] However, hyperplasia can also occur as a
pathological response, if an excess of hormone or growth factor is responsible for the stimuli. Similarly to physiological hyperplasia, cells that undergo pathologic hyperplasia are controlled by
growth hormones, and cease to proliferate if such stimuli are removed.[15] This differs from
neoplasia (the process underlying
cancer and benign tumors), in which
genetically abnormal cells manage to
proliferate in a non-physiological manner which is unresponsive to normal stimuli.[16] That being said, the effects caused by pathologic hyperplasia can provide a suitable foundation from which neoplastic cells may develop.[15]
Role in disease
Hyperplasia of certain tissues may cause disease. Pathologic hyperplasia in these tissues may occur due to infection, physiological stress or trauma, or abnormal levels of particular hormones, such as estrogen, ACTH, or cortisol.[17]
Types
Some of the more commonly known clinical forms of hyperplasia, or conditions leading to hyperplasia, include:
Endometrial hyperplasia – Hyperproliferation of the endometrium, usually in response to unopposed
estrogen stimulation in the setting of
polycystic ovary syndrome or exogenous administration of hormones. Atypical endometrial hyperplasia may represent an early
neoplastic process which can lead to
endometrial adenocarcinoma.[20] The development of endometrial adenocarcinoma from endometrial hyperplasia is a typical example of how the effects of pathologic hyperplasia can lead to neoplasia, and females who exhibit hyperplasia of the endometrium are indeed more likely to develop cancer of these cells.[15]
Hemihyperplasia – When only half (or one side) of the body is affected, sometimes generating limbs of different lengths.[21]
Intimal hyperplasia – The thickening of the
tunica intima of a blood vessel as a complication of a reconstruction procedure or
endarterectomy. Intimal hyperplasia is the universal response of a vessel to injury and is an important reason of late bypass graft failure, particularly in vein and synthetic vascular grafts.[22]
Focal epithelial hyperplasia (also known as Heck's disease) – This is a wart-like growth in the mucous tissues of the mouth or, rarely, throat that is caused by certain sub-types of the
human papillomavirus (HPV). Heck's disease has not been known to cause cancer.[23]
Myofibre hyperplasia (also known as
double-muscling) – seen in cattle, genetic mutations cause large muscles due to increased proliferation of myofibres and decreased adipose tissue.[24]
Sebaceous hyperplasia – In this condition, small yellowish growths develop on the skin, usually on the face. This condition is neither contagious nor dangerous.[25]
Compensatory
liver hyperplasia – The liver undergoes cellular division after acute injury, resulting in new cells that restore liver function back to baseline. Approximately 75% of the liver can be acutely damaged or resected with seemingly full regeneration through
hepatocyte division, i.e., hyperplasia. This is what makes living-donor liver transplants possible.[26]
^
ab"Prostate Enlargement (Benign Prostatic Hyperplasia)". National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK). U.S. Department of Health and Human Services National Institutes of Health. Retrieved 2015-05-30.
^"Hyperplasia". MedlinePlus Medical Encyclopedia. National Library of Medicine, U.S. Department of Health and Human Services National Institutes of Health. Retrieved 2015-05-30.
^Kemp WL, Burns DK, Brown TG.
"Pathology: The Big Picture". AccessMedicine. McGraw Hill Medical. Retrieved 2021-12-06.
^"Cushing disease". MedlinePlus Medical Encyclopedia. National Library of Medicine, U.S. Department of Health and Human Services National Institutes of Health. Retrieved 2015-05-30.
^"Congenital adrenal hyperplasia". MedlinePlus Medical Encyclopedia. National Library of Medicine, U.S. Department of Health and Human Services National Institutes of Health. Retrieved 2015-05-30.
^"Endometrial Hyperplasia". American College of Obstetricians and Gynecologists (ACOG). Retrieved 2015-05-30.
^"Hemihyperplasia - Glossary Entry". Genetics Home Reference. National Library of Medicine, U.S. Department of Health and Human Services. Retrieved 2015-05-30.