Most tissues of the body grow by increasing their cell number, but this growth is highly regulated to maintain a balance between different tissues. In adults most cell division is involved in tissue renewal rather than growth, many types of cells undergoing continuous replacement.
Internal monitors called checkpoints track each step of the cell cycle. In the cell cycle, there are three main checkpoints; one at the end of G1, a second at the transition of G2/M, and a third during the metaphase. Positive molecules of the regulator allow the cell cycle to proceed to the next level.
Mitosis, although continuous process, is conventionally divided into five stages: prophase, prophase, metaphase, anaphase and telophase.
