HON Dossier on Ageing


Mechanisms of ageing

    Organ ageing
       Brain ageing
       Sense ageing
       Endocrine system ageing
       Immune system ageing
       Cardiovascular system ageing
       Conjunctive tissue and skin ageing
    Cellular ageing
    Macromolecular ageing
     

 Proteins

       Lipids
       Genetic material
 
Mechanisms of ageing
Organ ageing

The ageing process manifests itself within numerous organs. Central nervous (particularly brain), immune, endocrine ad cardiovascular systems functioning are impaired with age. Alternations in conjunctive and muscular tissues are other familiar ailments common to ageing humans.

Brain ageing

Brain damage due to ageing alone (as opposed to pathological ageing) is minimal. Although the ageing brain may lose 100,000 neurons a year, the brain seems to compensate for these losses. This compensation could be positively influenced by intellectual challenge (by mental exercises). In fact, appropriate brain stimulation may cause brain cells (neurons), to branch wildly. This branching causes millions of additional connections (synapses), between brain cells and compensates cell loss.

Ageing is also often associated with memory loss and learning difficulties.

Although certain aspects of learning such as task acquisition seem to deteriorate with age, keeping the mind active aids effective learning throughout life.

To perform your own memory test.

Sense ageing

Eye ageing

Vision is a complex sense made up of the ability to see contrasts and sharpness of detail, and to evaluate the location of objects in the environment.

With age, eyes change. Among older people, low vision can result from specific eye conditions, such as cataracts, macular degeneration, glaucoma, and diabetic retinopathy, or from a stroke. In some cases medication or surgery are necessary to improve or prevent the worsening of vision-related conditions; in others the prescription of corrective lenses or rehabilitative services can help older people to maintain or restore their sight.

Age-related macular degeneration Test .

Ear ageing

Ageing is associated with hearing problems: words are hard to understand, another person's speech is difficult to understand, especially when there is background noise, certain sounds are annoying or loud, within the ear a hissing or ringing is heard in the background. Presbycusis (an ongoing loss of hearing linked to changes in the inner ear) is the most common hearing problem in older people. Tinnitus (a symptom associated with a variety of hearing diseases and disorders such as a ringing, roaring, or other sound inside the ears) is also common.

Endocrine system ageing

The endocrine system is particularly sensitive to age. Alterations may be due to the:

  • diminution of the synthesis or turnover of most of hormones:
  • impaired functioning of hormone receptors;
  • defective binding between hormone and its receptor;
  • premature programmed death (apoptosis) of hormone producing cells;
  • auto-immune reactions;
  • cancerous transformations.

Endocrine system alterations are linked to the apparition of several ageing related diseases such as diabetes, disorders in thyroid gland functioning and sexual hormones deficiencies.

In ageing men, a progressive diminution of circulating levels of androgens and testosterone is observed (andropause). This diminution is often treated by testosterone replacement therapy.

In women, female hormone production is progressively slowed and finally stops (menopause). It is treated by progesterone and estrogens replacement.

To compare your laboratory tests with international standards use the conversion table.

Immune system ageing

The immunological theory of ageing proposes that alterations in the immune system contribute to the changes associated with old age. With age, the immune system is thought to become less efficient, with a reduced capacity to deal with infection and a greater likelihood of auto-immune reactions.

Although it is well established that the functional properties of T cells decrease with age, its biochemical and molecular nature is poorly understood. The available data suggests that changes in the signal transduction machinery are responsible for the impairment of T cell function during ageing.

For further information about immunological alterations and ageing.

Cardiovascular system ageing

The cardiovascular system is composed of the heart and blood vessels.

The heart grows slightly larger with age and its performance changes. In addition, as one ages, blood vessels lose their elasticity. Consequently, normal blood pressure and blood pressure during exercise slowly increase as we age.

You can test your own risk of stroke.

Conjunctive tissue and skin ageing

The dramatic changes in the appearance of the skin with increasing age are due in part to a progressive destruction of the delicate architecture of the connective tissue components (collagen, elastin, extracellular matrix, fibroblastes).

Reactive oxygen species (ROS) are a major factor responsible for connective tissue and skin changes.

ROS are produced by normal cells (mitochondria, cytochromes). Their production is increased in response to environmental injury (exposure to UV, bacterial infection, imbalance of the oxydant-antioxydant state, smoking, and other factors in the environment). ROS are particularly harmful to cellular components: proteins, lipids, DNA and mitochondria.

Mitochondria, which are the energy-producing bodies within a cell, have their own genome. Mitochondrial DNA seems unable to counteract the damage inflicted by ROS, because of the lack of repair mechanisms and the proximity of the ROS production (in the inner mitochondrial membrane). Mitochondrial DNA alteration results in cell inability to produce energy, and to cell death.

You can learn more about ROS biology.

    Cellular ageing

    Most types of human cells have a natural limit to the number of cell divisions (proliferation). This limit is called Hayflick limit (named after the researcher who discovered it). If a cell's Hayflick limit is reached the cell becomes senescent and dies. The reason why the cell replication is not continuous is not known. Telomeres shortening or impairment in DNA methylation could be responsible for this limited cell capacity to proliferate (see below).

Macromolecular ageing

Cells are composed macromolecules: proteins, lipids and genetic material. Common features of cells from senescent tissues are an accumulation of abnormal proteins, lipid peroxidation and/or an impaired transmission of genetic information.

    Proteins

    With age, protein molecules are broken down or changed by (by isomerization, crosslinking, impaired turnover). Under normal conditions cellular proteins are repaired by "molecular chaperones" or are eliminated by proteolysis. With age, an imbalance between alteration and repair phenomena occurs. This imbalance results in the accumulation of abnormal proteins. A decrease in the amount of repairing proteins (such as "molcular cheperones" or Heat Shock Proteins) or a defect in proteolytic system efficiency could clearly contribute to such an accumulation.

    Lipids

    Lipids are major components of cell membranes. With age, lipids are oxidised (peroxidazed). Lipid peroxidation leads to the impaired functioning of cell membranes and may induce numerous pathologies including arteriosclerosis or Alzheimer’s disease.

    Genetic material

    With age, genetic material is altered at different levels. The stability of DNA is decreased, the DNA transcription and the translation of proteins are impaired. The alternation in the transmission of the genetic information results in accumulation or abnormal, no functional proteins (" error theory "), leading to cellular impairment, ageing and death.

    Telomeres

    At each cell division the shortening in telomeres (protecting structures at the ends of chromosomes ) is observed. The progressive shortening of telomeres may be a cause (or the cause) of cellular ageing. Telomeres shortening may appear to be the cellular clock that determines the number of times cells could divide and which weakens chromosomes to the point where cell division is no longer possible.

    DNA methylation

    DNA methylation plays a central role in genomic imprinting and embryonic development. Aberrations in DNA methylation have been implicated in ageing and various diseases including cancer.

 

 

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  http://www.hon.ch/Dossier/Ageing/part2.html Last modified: Fri Nov 1 2002