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| Ageing |
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| Ageing can be defined as the progressive deterioration in the structure and function of the cells, tissues, organ and organ systems of the organism with advancing age. |
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| The field of developmental biology that deals with the process of ageing is known as gerontology. |
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| The scientists who study the science of ageing are called gerontologists. |
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| Pace of ageing |
| The effects of ageing vary widely in different groups. Bacteria, viruses and many protozoans are free from ageing, but none of multicellular organisms live forever. Even under the most favourable conditions, some live for only a short period while others live for decades or even centuries. |
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| Example: Turtles live for about 150 years. Even different types of cells have different longevity. In general, cells that differentiate and stop dividing are subjected to changes of ageing than those that are capable of dividing throughout their life. |
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| Maximum life span |
| Maximum life span is the maximum number of years survived by any member of a species. Average life span is the average number of years survived by members of a population. |
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| Life expectancy is the number of years an individual can expect to live. It is based on the average life spans. |
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| Thus, maximum life span is the characteristic of a species while life expectancy is the characteristic of population. |
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| The maximum life span of wild animals is very difficult to obtain. This is because in the wild, they seldom die of old age. For this reason, maximum life span of wild animals is obtained from zoos. However these figures cannot be considered appropriate, as in zoos animals are not free but are in captivity. In this varied conditions, their maximum life span will also differ. |
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| The maximum life span of humans has been estimated to be about 121 years. This is based on the fact that a Japanese by name Shirechiyo Izumi lived for 120 years and 237 days. |
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| Advancement in science and medicine has reduced the mortality rate and increased the life span of humans. |
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| Ageing |
| Ageing is accompanied by impairment of physiological functions. This is termed as senescence. Senescence results in decreased ability to deal with a variety of stresses and an increased susceptibility of the body to diseases |
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| Symptoms of ageing at the level of the organism: |
 Heart - The efficiency of the heart decreases with increasing age. In a 70 year old man, the heart pumps only 65% blood per minute as compared to a 30 year old man. |
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 Oxygen uptake by blood - Oxygen uptake is reduced with advance in age. |
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 Decrease of blood volume - The production of RBC from the bone marrow decreases and so the volume of blood also decreases. |
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 Kidney - Kidneys become less efficient in extracting wastes from the blood. There is a reduction in the number of kidney tubules, which leads to a decreased output of urine and difficulty in passing urine. Bladder capacity decrease. |
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 Lungs - The capacity of the lungs for intake of air decreases. So there is a decreased oxygen supply to the various tissues. This leads to breathlessness and inflammation of mucous membrane. |
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 Digestive system - The number of taste buds on the tongue is reduced to about one-third. The secretion of digestive juices also decreases with old age. |
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 Body fat - There is redistribution of fat to deeper parts of the body from the skin. In women, fat is generally stored in the hips and thighs, while in men it is stored in the abdominal area. |
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 Retention of water - The capacity of body cells to retain water decreases. This makes the skin dry and wrinkled. |
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 Nerve impulse - The rate at which the nerve impulse is propogated reduces with age. Brain also loses some neurons. |
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 Muscles - Muscle mass in the body decreases by about 22% for women and 23% for men. |
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 Sight - Difficulty in seeing close objects begins by about 40 itself. In later ages, ability to distinguish finer details declines, they become susceptible to glare and greater difficulty sets in to see things at low levels of illumination. |
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 Hearing - Sense of hearing reduces with age. |
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| Cellular Changes During Aging |
| The outward signs of ageing are the result of changes taking place at the cellular and extracellular levels. |
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 Morphological changes: Accumulation of exhaustion pigments. The exhaustion pigments lipofusion, yellow pigments and brown deposits which are byproducts of unsaturated lipid oxidation, accumulate in the cell. |
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 Appearance of lipid vacuoles: Small lipid vacuoles appear in the cytoplasm. |
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 Decline in cell volume: Cells exhibit hypertrophy or a decrease in cell volume. |
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 Nuclear pykinosis: With advancing age, the nucleus shrinks and stains deeply. Such a nucleus is called pykinotic. This is due to the condensation of the nuclear material. |
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| Other changes associated with ageing are, |
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 Increase in cholesterol levels |
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 Increase in blood globulin |
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 Decrease in alkaline and acid phosphatases |
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 Decrease in cellular respiration. |
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| Sub Cellular Changes |
 Plasma membrane: The permeability of the plasma membrane decreases due to the accumulation of calcium in the membrane. |
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 Endoplasmic reticulum: In the cytoplasm of old cells, granular ER decreases. In the nerve cells, nissl granules are decreased. |
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 Mitochondria: Mitochondria become degenerated in the cells of old tissues. This leads to a reduced rate of respiration. |
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 Nucleus: With ageing, there is an accumulation of chromosomal aberration and gene mutations. This disturbs the normal functioning of the DNA. |
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| Extra Cellular changes |
| There is an increase in the amount of collagen proteins deposition in the intercellular spaces. This influences the permeability of cell membranes, affects the speed of diffusion of substances in and out and significantly influences the process of ageing. |
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