aging (redirected from aging by teeth)

aging, in biology, cumulative changes in an organism, organ, tissue, or cell leading to a decrease in functional capacity. In humans, aging is associated with degenerative changes in the skin, bones, heart, blood vessels, lungs, nerves, and other organs and tissues. The branch of medicine that deals with the disorders of aging in humans is geriatrics.

Biologists have advanced a variety of theories to explain aging, but most of them agree that this process is largely determined by genes. This view is suggested by the great range of lifespans among different animal species—from a few days in the fruit fly to more than 100 years in some tortoises. Scientists have recently learned how to double the lifespans of such laboratory organisms as roundworms and fruit flies through genetic manipulation, and mutant genes in mice have been observed to have a comparable effect in postponing aging.

At the cellular level, an important recent finding has been that the lifespans of cells in the human body are determined by strings of DNA (genetic material) called telomeres, which are located at the ends of the chromosomes. Each time a cell divides, the telomere becomes shorter; the senescence and death of the cell is triggered when the telomere is reduced to a certain critical length. Telomerase, an enzyme that can intervene in this process, is being closely studied in relation to cancer as well as aging.

Environmental factors have been observed to affect aging as well. Scientists have discovered that they can significantly postpone aging in mice by providing them with very low-calorie diets, and recent studies of rhesus monkeys on low-calorie diets appear to be having the same results. It is believed that these diets slow the aging process by lowering the rate at which tissue-damaging substances called free radicals are produced in the body. One aim of these studies is the development of antioxidant drugs that could slow the aging process in humans by protecting against free radicals. The use of testosterone, melatonin, human growth hormone, and other hormones as "anti-aging" treatments is medically unproven and potentially dangerous, as the hormones can have damaging side effects.

Bibliography

See L. Hayflick, How and Why We Age (1994); publications of the National Institute on Aging.

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aging

Gradual change in an organism that leads to increased risk of weakness, disease, and death. It takes place in a cell, an organ, or the total organism over the entire adult life span of any living thing. There is a decline in biological functions and in ability to adapt to metabolic stress. Changes in organs include the replacement of functional cardiovascular cells with fibrous tissue. Overall effects of aging include reduced immunity, loss of muscle strength, decline in memory and other aspects of cognition, and loss of colour in the hair and elasticity in the skin. In women, the process accelerates after menopause. See also gerontology and geriatrics.

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ageing, aging

the change of properties that occurs in some metals after heat treatment or cold working

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aging [′āj·iŋ]

(acoustics)

The process by which the pressure disturbance from a passing aircraft is distorted as it propagates away from the aircraft, causing the signature to stretch out in duration and length, lose detail, and form shock waves.

(biology)

Growing older.

(chemistry)

All irreversible structural changes that occur in a precipitate after it has formed.

(electricity)

Allowing a permanent magnet, capacitor, meter, or other device to remain in storage for a period of time, sometimes with a voltage applied, until the characteristics of the device become essentially constant.

(electromagnetism)

Change in the magnetic properties of iron with passage of time, for example, increase in the hysteresis.

(engineering)

The changing of the characteristics of a device due to its use.

Operation of a product before shipment to stabilize characteristics or detect early failures.

(materials)

Change in the properties of any substance with time.

Change occurring in powders or slips with the passage of time.

Curing of ceramic materials, such as clays and glazes, by a definite period of time under controlled storage conditions.

(metallurgy)

Change in properties of an alloy or metal which generally proceeds slowly at room temperatures and faster at elevated temperatures.

Strain relief, occurring through long storage outdoors under varying temperatures, of iron castings intended for use as toolroom plates or lathe-bed supports.

A second heat treatment of an alloy at a lower temperature, causing precipitation of the unstable phase and increasing hardness, strength, and electrical conductivity.

(nucleonics)

The slowing down of neutrons.