Jethalal S. Zaveri
Growth
The life of a human, from conception to death, may be viewed as a continuous process—a series of events that follow one another in a programmed sequence, varying in details but leading to the same ultimate conclusion.
A living organism grows by the intake of food which is broken down into its constituent simpler substances which are then re-assembled into specific needs of the organism. Waste products are excreted, but the total of the materials, taken in, exceeds the amount returned to the environment, and there is a net increase in the size and weight of the organism. Cell-division—increasing the total number of cells—is the main process of growth.
Growth in size and weight, however, is not the whole story. The dramatic development of a fertilized ovum into a baby and that of a baby into an adult involve another important process, viz. differentiation—an increasing specialization of cells for specific functions. During childhood, the body and its parts only grow in size, but are constantly modified and reshaped permitting the mastery of new skills. During adult life, active growth ceases; cells that wear out or are destroyed by accident or disease are replaced and a dynamic equilibrium is maintained. But ultimately the repair processes become less efficient and cannot adequately replace the day-to-day losses. Slowly various body-functions deteriorate.
Human growth is not a steady process. Dropping steadily throughout prenatal life, the rate of growth continues to fall after birth. In the nine months from conception to birth, a human fetus, increases its size and weight about 10 billion fold. In the first year after birth, it triples its weight and adds about 50 percent in height. Then follow a period of consolidation and the growth settles down for a time to a steady 2 to 3 kgs. and 5 to 7 cms. a year. The flow of sex hormones during adolescence sparks a sudden growth spurt adding as much as 15 to 18 cms. in a year. After this spurt, there is a rapid deceleration. Growth in height stops entirely by the age 18 to 21 in boys and 16 to 18 in girls. The onset of maturity may be delayed by a variety of factors such as undernourishment, but growth eventually ceases.
The programmed sequence of growth and its completion may hold important clues to the prolongation of vigorous life. Interactions of the hormones of the pituitary with other hormones and with control-centres in the brain may be key factors in the working of the built-in clocks that determine human growth and development. Thyroid hormone also stimulates growth, especially of the skeleton and nervous system through a general stimulation of metabolism. During the adolescent growth-spurt, sex hormones produced by the gonads and adrenal cortex further stimulate growth. Cells, too, seem to have a built-in clock that determines their specific life-span. Some believe that growth ceases when the hormonal processes that trigger D.N.A. synthesis and cell division somehow break down in aging cells. The maximum number of divisions, liver cells and other would undergo, in the human body, in a life-time of 100 years is about 50[1]. After this they cease dividing and ultimately die.
Although growth in height ceases at adulthood, there may be a net increase in weight in later years. The tendency to gain weight in middle age occurs, because there is usually a decrease in physical activity but no comparable reduction of appetite. The sedentary adult, thus, takes in more calories than the body can use up and the excess is stored as fat[2]. A careful program of exercise and diet only can stop the weight-increase.
Aging
Aging or senescence is a biological process characterized by a gradual deterioration of the structures and functions of the body, resulting in an increased susceptibility to accident and disease. No sooner has maturity been reached than a progressive decline in the body's efficiency begins. Different organs and tissues age at different rates. Nerve and muscle-cells show an earlier decline in the functional capabilities than tissues such as those of liver and pancreas, in which active cell-divisions continue longer.
Some of the most tragic changes are observed in the central nervous system. A combination of loss of nerve cells, which are not replaced, a slowing of the nerve-conduction and reduction of circulation to the brain results in a progressive decline of mental efficiency. The sense of the aging person become less acute. There is a progressive hearing loss. The eyes become prone to various degenerative diseases and a reduction of the ability of the eye muscles to accommodate the lens results in hypermetropia i.e. farsightedness. Taste is also dulled as taste-buds are progressively lost. A lengthening of reaction time and growing lapses of memory become apparent. Learning is more difficult for older people, partly because of the reduced mental efficiency and partly because of interference from previously acquired knowledge.
Various degenerative changes occur in the circulatory system. The heart-muscle may be partially replaced by fibrous or fatty material. Deterioration of the elastic fibres stiffen the artery-walls and calcified fatty deposits within them may weaken them so that they burst when the blood-pressure is raised by emotion or straining or may lead to circulation-blocking blood-clots.
Calcium salts are deposited around the fibres resulting in the loss of resiliency of the chest and the stiffness of movement of the joints. While calcium is creating problem by being deposited in places where it should not be, it is being dissolved out of the bones, weakening them and making them more susceptible to fractures.
Aging upsets the fluid-balance; there is a gradual loss of tissue fluid throughout life, causing them to dry up. Filtration-rate in the kidneys drops. Complex hormonal changes occur. In women, it brings a dramatic cessation of menstruation (menopause). In men the deterioration of sexual activity is more gradual, it declines and may cease entirely.
At least some of the above changes are, however, avoidable effects of ignorance, attitudes and modern conditions. In people living away from the barrage of noise that continuously assails the ears of city-dwellers, a high degree of hearing acuity is retained upto extreme age. The inactivity resulting from the attitude to "take it easy" may be a significant factor in the loss of calcium from the bones. The resultant weakness and fragility of the bones compel further inactivity thus perpetuating a vicious cycle. In one study, a group of 60 year olds was placed on a supervised programme of exercises. 10 years later they were found to be physiologically younger than they were at 60. If we know precisely how the body ages, we might be able to modify and perhaps prevent and even reverse the aging process. Researchers in aging scrutinize various body-systems as possible biological clocks, e.g., it is known that the thymus reaches its zenith of development in adolescence and then gradually atrophies. The levels of thymosin in the blood fall in the increasing age. Simultaneously, activity in the immunological system intensifies. But the decrease in efficiency of immune surveillance by the T-cell results in the imperfect lymphocytes making errors of the "self cells for enemy invaders. Similarly various control-centres of the hypothalamus and its hormones which work through the pituitary to control and coordinate glands of the endocrine system, have been implicated in the functioning of various cyclic processes in the body. The aging process may be started by blocking the action of thyroxin. Other researchers consider the environmental influences on the body and its cells to accelerate the aging process. They view the major causes of aging as lying in the "wear and tear" resulting from the continual stress condition, radiations and chemical mutagens.
The information-molecules of the cell gradually become blurred with errors reducing the efficiency of the protein-synthesizing apparatus. The faulty enzymes produced may, then, cause a further deterioration of the templates, compounding the damages. The accumulation of enough non-functional or abnormal cells in an organ will impair its functioning and sine the organs of the body are interrelated, the deterioration of one organ may produce a spreading wave of damage to others, ultimately resulting in aging and death.
Thus aging is a complex process with many contributing factors not necessarily mutually exclusive. "Haylick limit" of cells-division agrees with the concept of an inherently finite life-span with an upper limit for human beings of about 110 to 120 years. Hence it is clear that any effort to prolong life beyond this limit is not likely to succeed. Though the actual life-span could never be changed, knowledge of some of the factors discussed above would not only reduce the probability of dying in younger age-groups but also extend the period of vigorous life, avoiding the miseries of old age.
Knowledge of the role of nutrition and dieting could be used in checking the tendency to gain weight in middle age. Deficiencies of vitamins C and B which accelerate the aging process could be avoided. Careful control on the intake of salt, sugar and fat would prevent the development of hypertension,
hardening of the arteries and overloading the heart. Continuing physical activities and a regular programme of exercises including breathing exercises would keep one physiologically young for a long time, regular practice of relaxation will prevent the damage to the cells, revitalising and rejuvenating them. Certain meditational practices such as concentrated perception of psychic centres would produce rejuvenating effects on thymus, prevent the "aging hormone" blocking the action of thyroxin and generally balance and harmonise the synthesization of hormones of the endocrine system. It would also prevent and reverse the impairment of mental functions (due to degenerative changes in the brain) which is the most pitiful aspect of senility.
Death
Death may be defined as the cessation of all metabolic processes. In human being, death usually results from the failure of some vital organ, due to accident, disease or degeneration. The effects of the failure spread throughout the inter-related systems of the body. Regardless of which organ was the first to fail, the effects ultimately reach the circulatory system and the heart stops. Deprived of the oxygen and nutrients delivered by this system, the cells of the body begin to die off. Nerve cells are the most vulnerable: irreparable brain-damage sets in about four or five minutes after the stopping of the heart. Death of the cells means rapid and irreversible changes in their structure and analysis of their membranes and contents, because the organizing influence is gone.
At one time, stoppage of the heart was the accepted definition of "clinical death". Yet, now it is often possible to resuscitate a person who has seemingly 'died' by electrical stimulation or even mere manipulation of heart and lungs. Certain enzyme-levels in the cerebrospinal fluid have been found to be correlated recently with the true status of the body.
