Hyperplasia is an increase in the number of cells of an organ/tissue, often secondary to a stimulus or stress. This process can be contrasted with hypertrophy, an increase in the size of cells, however these processes frequently co-occur 1.
Hyperplasia occurs due to stimulation by growth factors and hormones resulting in increased cellular division and proliferation from stem cells. This can be physiological or pathological 2.
An example of physiological hyperplasia occurs in the bone marrow, which produces more erythrocytes in the setting of blood loss.
Pathological hyperplasia often occurs due to overstimulation of tissues by growth factors. An example is endometrial hyperplasia, which happens when there is a relative excess of estrogen, causing increased endometrial thickness and creating an environment of increased risk of dysplasia and subsequent malignant transformation.
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