The human body consists of 50,000,000,000,000 or fifty trillion cells, and each cell has 46 chromosomes which are the structures in the nucleus containing our hereditary material, the DNA. The ends of all chromosomes are protected by so-called telomeres. The telomeres serve to protect the chromosomes in much the same way as the plastic sheath on the end of a shoelace. But each time a cell divides, the telomeres become a little bit shorter and eventually end up being too short to protect the chromosomes. Popularly speaking, each cell has a multi-ride ticket, and each time the cell divides, the telomeres (the chromosome ends) will use up one ride. Once there are no more rides left, the cell will not divide any more, and will, so to speak, retire. But some special cells in the body can activate telomerase, which again can elongate the telomeres.