Short introduction Definition Theorieses of aging causes of aging life span Aging can be defined as the time related deterioration of the physiological functions necessary for survival . Or Can be define as increase in impairment in Physiological functions with age , Increased in suspectebility to diseases and decrease in ability of fertility aging is the impact of time on the human body, and it occurs on multiple levels: Cellular changes Extracellular changes 1) cellular changes Causes of aging Cellular senescence and aging Telomere shortening: linked to life expectancy and aging Mitochondrial dysfunction and aging Oxidative stress Stem cell exhaustion Developmental biology by T.subramonium Developmental biology 6th edition