The process of aging begins in the body’s smallest units, the cells. How and why cells age is a subject of debate—though a few mechanisms are becoming clear
Aging ranks with sleep as one of the fundamental mysteries of human biology. What causes the body to slow down, its cells to stop dividing, and its organs to fall prey to increasing illness and disability? No one has definitive answers to these questions, but theories can be grouped into two camps: gradual damage over time and genetic programming.
The first group of theories holds that the body ages because of wear and tear that accumulates in the tissues over the years. Waste products build up in cells, backup systems fail, repair mechanisms gradually break down, and the body simply wears out like an old car.set to a particular timetable for each species. Support for this theory comes from animal studies: Scientists have been able to cause an increased life span in some animals by altering just one gene. Biologists point out that from an evolutionary point of view, the effects of natural selection greatly decline after reproductive age. Evolution favors genes that are beneficial early in life, putting the body’s resources into reproduction and leaving fewer available for long-term maintenance.Please be respectful of copyright. Unauthorized use is prohibited.: In this magnified cross section of compact bone, osteocytes —cells involved in bone remodeling—branch out to connect with other cells.: In this magnified cross section of compact bone, osteocytes — cells involved in bone remodeling—branch out to connect with other cells.The process of aging begins in the body’s smallest units, the cells. How and why cells age is a subject of debate, though a few mechanisms are becoming clear. In the early 1960s, biologistdiscovered that cultured cells would divide only an average of 50 times before they stopped—a number that has become known as the Hayflick limit. With the exceptions of stem cells and cancer cells, this limit applies to all human tissues, though cells from older people divide fewer times.telomeres . Telomeres are stretches of DNA that cap the ends of chromosomes, protecting them from damage and keeping them from fusing with other chromosomes. Researchers found that each time a cell divides, about 50 to 100 of the telomere’s nucleotides are lopped off. When the telomere reaches a minimum length, cell division stops altogether.
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