Cellular Adaptation III: Hyperplasia

Hyperplasia refers to an increase in the number of cells within a tissue or organ, typically driven by elevated cell division to support tissue repair and regeneration.

Tissues such as the epidermis, intestinal epithelium, and bone marrow possess strong hyperplastic potential, whereas bone, cartilage, and smooth muscle have limited capacity for hyperplasia.

Hyperplasia generally arises through two mechanisms. One mechanism involves stimulation by growth factors or hormones. After cell injury, these signals prompt surviving cells to re-enter the cell cycle and begin dividing.

The other mechanism depends on the activation of tissue stem or progenitor cells, which generate mature cells to replace damaged ones.

Hyperplasia may be physiologic or pathologic.

Physiologic hyperplasia is a normal response that maintains tissue balance, such as the endometrial proliferation during the menstrual cycle.

Pathologic hyperplasia results from excessive stimulation, such as thyroid hyperplasia caused by chronic TSH elevation in iodine deficiency.