According to the most recent scientific estimates there are roughly 30 trillion cells in the human body, all of which arise from one unified cell through various cycles of division. If you were to write that number out that's 30,000,000,000,000! The process of cellular renewal continues throughout life as old and weak cells are replaced by new ones, however, after the age of 25 your body's cells begin to decline.
Stem cell therapies and regenerative medicine are new and upcoming medical treatments. Stem cells are undifferentiated cells that reside throughout the body that give rise to other kinds of cell types (neurons, heart cells, bone cells, etc.) Recently these cells have been studied for anti-aging effects, reversing blindness, regenerating cartilage, etc.