At the molecular level, lipofuscins, or aging pigments, appear with increasing frequency in non-dividing cells. Because they contain oxidized lipids, it has been theorized that they are products of oxidative chemical reactions such as those involving free radicals (Ricklefs and Finch, 1995, 34).
Modifications in Hormonal and Neuroendocrine Systems
The pituitary, ovaries, and testes are part of a system of glands that secrete hormones into the blood stream and which are controlled by the brain. This system is called the neuroendocrine system. At puberty, a signal is sent by the pituitary gland to the ovaries and testes, telling them to produce more sex hormones such as estrogens and progesterone in women and androgens in men. In women, menopause, a stage in which the reproductive system is shut down, is reached. From this point in a woman=s life these hormones are no longer produced and many changes are experienced. Because some neurons can become Aaddicted@ to estrogens, the absence of these hormones induces the brain to respond in different ways, such as sending a surge of blood to the skin. This is sometimes called a Ahot flash@ (Ricklefs and Finch, 1995, 37). Unlike hot flashes, a woman may experience harmful or dangerous changes because of menopause: osteoporosis, or the loss of compact bone is accelerated because bone-mineral metabolism is dependent on estrogen. Once this condition has reached a certain stage, it reduces the ability of bones to support body weight. It also immensely elevates the risk of bone fractures. In fact, as a woman increases in age, her risk of bone fracture due to osteoporosis increases exponentially (Ricklefs and Finch, 1995, 43).
In men, the number of abnormal sperm, incidence of lower testosterone production, and incidence of impotence have been found to increase with age. Because the brain controls the pulses of testosterone, it can be said that some of these changes arise because of different signals in the brain (Ricklefs and Finch, 1995, 44).
The hormonal and neuroendocrine theory collects evidence mostly from a female way of life, yet both men and women experience the aging process and many of the same characteristics that go with it.
The knowledge that the process of aging is very complex can be deduced from the simple fact that there are many entirely different, yet plausible, theories of how aging works. In fact, the possibility that several of these theories are connected, or play a combined part in aging is not far fetched. Yet because the process of aging is so multifarious, just how humans complete or even begin the transition from youth to old age remains a mystery to some extent. However, with new evidence and proof supporting some of these hypotheses, opportunities for a healthier, longer life may arise.
References
Allis, S. et al.., 1996. Older, Longer. Time Magazine. Fall 1996:60-64
Keeton, K. 1992. Longevity: the Science of Staying Young. Penguin Books USA Inc., New York, NY.
Kronhausen, E. et al. 1989. Formula for Life. William Morrow and Company, Inc., New York, NY.
Lafferty, E. et al., 1996. Can We Stay Young?. Time Magazine.
25/11/96:53-62
Ricklefs, R.E. and Finch, C.E. 1995. Aging; A Natural History. W.H. Freeman and Company, New York, NY.
Bibliography
Aging, The Concise Encyclopedia of Science and Technology, 1978 ed.
Allis, S. et al.., 1996. Older, Longer. Time Magazine. Fall 1996:60-64
Keeton, K. Longevity: the Science of Staying Young. New York, NY: Penguin Books USA Inc., 1992.
Kronhausen, E. et al., Formula for Life. New York, NY: William Morrow and Company Inc., 1989.
Lafferty, E. et al., 1996. Can We Stay Young?. Time Magazine.
25/11/96:53-62
Ricklefs, R.E. and Finch, C.E. Aging; a Natural History. New York, NY: W.H. Freeman and Company, 1995.
Segall, P. and Kahn, C. Living Longer, Growing Younger. Toronto, ON: Random House of Canada Limited, 1989. New York, NY: Random House Inc., 1989.