senescence

With aging, various physiological, metabolic, and functional changes of various body systems and various organs and tissues gradually appear with age. And aging includes a longer period of time, including changes that have occurred since the beginning of development. There are four characteristics of aging: universal, progressive, expendable and endogenous. Aging is a normal development process and a physiological process, which is related to genetic and biological, psychological and social factors. People generally mature to 20 to 25 years of age, and some organs (such as the brain) generally mature to around 30 years of age. Later, biological aging gradually appeared. The aging rate is slow and gradual in the first 20 to 30 years, and the aging rate is accelerated to a certain age. However, the aging individuals are quite different, and the aging rates of various organs of the same individual are not synchronized, and the same change in the performance of different organs is also different, such as the degree of arteriosclerosis in the heart, brain, and kidney is not completely synchronized. Simple functions (such as stroke volume or renal excretion) are less affected by aging than complex functions (such as the response time of the nervous system and the ability of the body to adapt). This difference is significantly related to genetic, occupational and physical activity. Therefore, calendar age (the period of time since birth was expressed in time) is not a reliable indicator of life expectancy, and biological age is more accurate. Biological age is calculated based on the functions and metabolism of major systems and organs (such as the cardiovascular system, respiratory system, nervous system, and kidneys), and aging signs (such as some characteristics of the skin). The biological age may be lower or higher than the calendar age, or they may be equal. The factors that affect the life process include internal factors (such as heredity) and external factors (such as biological, social, and psychological factors). The in vitro culture of human fibroblasts has confirmed that the number of cell divisions is limited; it has been suggested that the number of cell divisions is related to the life span of the body from which it comes. A person's life expectancy is 110 years, and this life limit is genetically controlled. However, when the human body is exposed to the external environment, various biological factors (such as bacteria, viruses, etc.), physical factors (ionizing radiation, ultraviolet radiation, noise, microwaves, etc.), chemical factors (toxic chemicals, common ones include mercury, lead, Arsenic, 3,4-benzopyrene, pesticides, organic solvents, etc.) can promote human aging; social and psychological factors are also closely related to human aging. The aging process that naturally occurs after sexual maturity is physiological aging. The aging process caused by external factors (including diseases) on the basis of physiological aging is called pathological aging. But the two are difficult to distinguish strictly, and they often coexist and affect each other. With the research on the mechanism of aging, there have been attempts to use many methods, mainly drugs to delay aging.