The division, growth and maturation (differentiation) of cells in healthy tissue are subject to diversified and very accurate control mechanisms. The increase in the size of the cells while the number of cells remains the same is called hypertrophy (e.g., muscle tissue due to training). Hyperplasia is understood as the increase in the number of cells while the cell size remains the same (e.g., mucosal hyperplasia). Tissue which regresses (reduction in cells, reduction in cell numbers) is called atrophy (e.g., atrophy caused by inactivity in the case of a plaster cast).