Why we are getting old?

The answer is simple,the 'errors'.The errors that happening during cell multiplication and by the influences of external factors. So many  changes happens in DNA every year,most important one is the shortening of telomeres. A telomere is the tail end of chromosomes. The free radical theory of -ageing, which devolved in1950 says that the reactive oxygen species(ROS)  produced during mitochondrial functions react with their DNA (mtDNA)  and other cell organelles, makes sever damage and declined mitochondrial functions that leads us to aging. ROS is produced when mitochondria make energy from food particles,when we eat more the mitochondria produce more energy and more ROS also evolved as by product. So having a comparatively limited amount of diet and  anti oxidant rich food,such as green vegetables fruits etc can increase life span.

Old age
In the year 1961 an American scientist L.Hayflick discovered that human cells have limited capacity to divide. Human cells are not able to divide again after 50 cell divisions,this condition is called Hayflick limit. The cells gradually lose it's biological efficiency and said to be aged. Later A.M olovnikov proposed the telomere theory of aging(telomeres are the tail end of chromosomes).The theory says that,after each cell division the length of telomeres become shorter and shorter. When it is too short the cell cannot divide any more. When we born the the length of telomere in our WBC(white blood cells) can be measured 8000 base pairs and when we become elder the length will be only 1500 base pairs.

According to neuro endocrine theory, age changes happened in hypothalamus, pituitary and thyroid glands or the combined actions of these glands. decreased production of certain hormones and functional decline of neurons are said to to be the main reason for aging.

Thymus,a very important endocrine gland,start to shrink in early teen age and gradually replaced by thick fatty tissue, by a process called involution, thymas is a very important organ in human body,which is a lymphoid organ as well as an endocrine gland. Thymus secrete thymopoitn, thymulin, thymosin etc,and small amount of melatonin and insulin. T cells are trained and matured in thymus,generally 3 types of T cells are there,they are cytotoxic helper and regulatory types T-cells protect us from infections,immune disorders, and cancer like diseases. why we losing such an important organ in our early life? is it pre programmed?

Cells committed suicide when they are infected with viruses or its DNA damaged and cannot be repaired, the process is known as apoptosis.

We know after 65 our immune system became weak,we don't have enough T cells to fight and eliminate viruses and other pathogens so apoptosis rate may increase in our old age.

Our cells also subjected to DNA methylation,this involve adding a methyl group (a carbon and three hydrogen atoms), to the area of DNA which sets this area of gene to off mode,then particular function will not work,if examine how much DNA is methylated then we can estimated the biological age. Some genes also hyper methylated with age.

Environmental damage to DNAs, proteins and fats, are another reason for aging. After the age of 20 human produces 1% less collagen in the sin each year,deficiency of collagen caused the skin become more brittle. 80% of skin wrinkling is the result of UV radiation from the sunlight

In the case of a well known human disease,Werner's syndrome, a mutated gene causes people older in their teen age,the mutated gene supposed to be involved in DNA maintain function

Conclusion 

We have lot of theories and scientific inventions on aging,but exact reason of aging is not yet understood. Thousand of chemical reactions are taken place inside our body and each reaction is perfectly catalyzed by different biological enzymes and every day thousand of products and byproducts are produced. Are these byproducts harm ful to us?how they eliminated? very complicated. Today science is well developed in all Fields, but not yet understood  the exact reason for 'why we are getting old'? l hope  soon we will found the cause and we will dicide how long we have to live in this beautiful world.

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