Ageing

Ageing

(i) Definition : Ageing is the show deterioration in the structure and function of body cells tissues and organs of an animal and starts after the adulthood.

(ii) Gerontology : The field of developmental biology that deal with the process and problems of ageing is known as gerontology – (Gr. geron = old man; logos = discourse). The scientists involved in the science of ageing are called gerontologist.

(iii) Life cycle and life span : In all metazoan animals, the life cycle includes two developmental period; embryonic period (pre-natal developmental period) which extends from zygote to offspring till hatching or birth, and post embryonic period (post-natal developmental period)- which includes growth, adulthood, reproduction, ageing. Thus, the life cycle comprises five main events : birth, growth, maturity, old age and death, that follow in the sequence named. Maximum life span is the maximum number of years survived by any member of a species, while average life span is the number of years survived by members of a population. Life expectancy is the age at which half the population still survives. The life span varies greatly in different organisms :

Maximum life span of human has been found to be about 121 years. Shirechiyo Izumi of Japan died due to pneumonia at the age of 120 years and 237 days in 1986.
Average life span of women is longer than men while the biological process of ageing is faster in human male than in human female. No organism lives for ever. (It is believed that Hydra is immortal as it does not undergo ageing). Every organism dies of old age if not killed earlier by an accident, a predator, aparasite or a disease.

(iv) Why old age ends in a natural death : Though it is difficult to give a categorical answer, certain factors that lead to death in old age are known. During the growth period, new cells are formed faster than the rate of death of old cells. But after the maximum growth, the metabolic rate declines and rate of formation of new cells is lower than the rate of death of body cells. So the repair of damaged cells is not complete and a slow deteriorative process starts. In human beings, it starts after the age of 30 years. But in certain cases, deterioration in structure and function of cells may start during childhood or even during prenatal life e.g. hearing efficiency of ear and atresia in ovary.  As the organism grows older,

(a) The metabolic activities gradually decline.
(b) Capacity to replace the worn out cells decreases.
(c) The power to repair the worn out tissues and organs decreases.
(d) Resistance power to diseases is lowered.
(e) Lowered adaptability.
(f) Finally, non-functioning of some vital organs like heart, brain, kidneys, lungs or liver.
So with ageing, there is an impairment of physiological functions, called senescence and ultimately leads to death.
Peak of activity : In humans, generally speaking, the peak of activity is thought to reach at about 30 years of age. Thereafter, the body shows signs of senescence, i.e., deterioration and loss of normal function. From the age of about 30 years, the human body becomes functionally less efficient by about 0.8% every year. It is a biological process.

(v) Deterioration data of an old person : A 75 years old man, for instance, has, as compared to a 30 years old person, about 64% less taste buds, about 44% less renal glomeruli about 20% less nerve cells in the brain, and about 37% less axons in the spinal nerves. His heart pumps 35% less blood and sends 20% and 58% less blood to the brain and the kidneys respectively. His lungs have 44% less vital capacity and provide about one-third less oxygen to the blood per minute. His kidneys have 31% lower rate of glomerular filtration. His nerve impulses are propagated at a rate about 10% slower. At the age of 30, the height starts decreasing indetectibly, it decreases by 0.3 cm. at 40, by 2 cm. at 50 and by 2.5 cm. at 70.

(vi) Changes in ageing or symptoms of ageing : Gerontalogist have worked out a large number of changes that accompany ageing. These are discussed below under three heads –
(a) Changes at organ level : During ageing, different organs and organ systems show different rates of decline e.g.

(1) Heart : With increasing age the efficiency of heart decreases. In a man of 70 years, the heart pumps only 65 per cent blood per minute as compared to a 30 years old man. Consequently, the blood going to the brain and kidney is reduced to 80 percent and 40 percent respectively.

(2) Oxygen uptake by blood : At the age of 20 blood takes about 4 litres of oxygen per minute, while in a man of 75 years, it takes only about 1.5 litres of oxygen in the same period.

(3) Decrease of blood volume : The production of new RBCs from the bone marrow declines and consequently the volume of blood also decreases.

(4) Kidney : The number of kidney tubules is found to reduce to half in the old age. As a result the volume of urine decreases. This creates lots of other urinary troubles and also causes body ache, low back and difficulty in passing urine.

(5) Lungs : The capacity of lungs for intake of air decreases. This leads to reduction in the oxygen supply to different tissues. Therefore, old persons suffer from breathlessness and inflammation of mucous membrane.

(6) Digestive system : The number of taste buds on tongue reduces to about one-third. The secretion of digestive juices also decreases with old age. This may result in indigestion. loss of appetite, dyspepsia, constipation and gas formation.

(7) Retention of water : The capacity of body cells to retain water also decreases with the result, the skin in old persons is dry and wrinkled.

(8) Nerve impulse : The rate of nerve impulse propagation reduces with age. The decline is about ten percent in man of 75 years as compared to that of 50 years old person.

(9) Increased mineral deposition in the bones which become brittle and easily fracturable.

(10) Muscle tissue degenerates due to biochemical changes in the muscle cells or neuromuscular junction. This greatly reduces the muscular strength. Without exercise, estimated muscle mass declines 22 percent for women, and 23 percent for men. It can be prevented by regular exercise.
(11) Thymus is almost microscopic by the age of 70 years. This lowers the number and functioning of T-lymphocytes which lowers the immunity against the antigens.
(12) Hair start greying or falling at the age of 40 due to reduced rate of protein synthesis.
(13) Menopause in female at an average age of 52 years.
(14) Body becomes thin, shrivelled and stooping.
(15) Decline in hearing power begins after the age of 10 years. It declines steadily upto 50 years of age after which the rate of decline is much slower. Hearing declines faster in men than in women.
(16) Eyes : Accommodation power of eye starts declining in the 40s; ability to distinguish fine details may begin to decline in the 70s while there is increased susceptibility of eyes to glare and more difficulty in detecting moving objects from 50 years onward. It is generalised that the human body becomes functionally less efficient from the age of 30 years onward by about 0.8% every year. So, the age of 30 years is a turning point in the process of development.