Hyperplasia

Hyperplasia (or "hypergenesis") is a general term referring to the proliferation of cells within an organ or tissue beyond that which is ordinarily seen. Hyperplasia may result in the gross enlargement of an organ, the formation of a benign tumor, or may be visible only under a microscope. Hyperplasia is considered to be a physiological response to a specific stimulus, and the cells of a hyperplastic growth remain subject to normal regulatory control mechanisms. This stands in contrast to neoplasia (the process underlying cancer and some benign tumors), in which genetically abnormal cells proliferate in a non-physiological manner which is unresponsive to normal stimuli.

Hyperplasia may be due to any number of causes, including increased demand, chronic inflammatory response, hormonal dysfunctions, or compensation for damage or disease elsewhere. 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.

Hyperplasia may also be induced artificially by injecting hormones such as IGF-1 and human growth hormone. Perhaps the most interesting and potent effect IGF has on the human body is its ability to cause hyperplasia, which is an actual splitting of cells. Hypertrophy is what occurs during weight training and steroid use and is simply an increase in the size of muscle cells. With IGF use, one is able to cause this hyperplasia which actually increases the number of muscle cells present in the tissue. Weight training and, more dangerously, anabolic steroid use enables these new cells to mature in size and strength. In addition, animal tests have shown that stretching a muscle can trigger hyperplasia though this phenomenon has yet to be confirmed in humans.