CELL DIFFERENTIATION
The final step leading to cell specialization is cell differentiation. Differentiation is a maturing process during which a determined cell becomes a recognizable, specialized cell. External stimuli, such as growth factors, trigger cells to differentiate. Once differentiated, these specialized cells are usually terminal and nondividing, though some may be induced to divide following injury.

Differentiated cells produce and use specific proteins characteristic of their differentiation type. For example, red blood cells produce hemoglobin to help transport oxygen, and muscle cells produce myosin to help with muscle contraction. Differentiated cells often assume characteristic shapes, such as columnar epithelial cells and star-shaped astrocytes.