Introduction: Biological Consequences Of Old Age
With the accomplishments of biomedical researchers, the life expectancy of the human population has bolstered up. The major factor responsible for the increased survival rates was the improvement of public health. The provision of clean water, immunization, health care, and a better lifestyle with good infrastructure facilities have improved the health conditions of the population. From the biological viewpoint, aging is characterized by the intrinsic deterioration of body functions and, eventually, death. Aging alters the composition of the body cells and organelles. The loss of body mass, bone density, normal body processes are the early symptoms of aging. The older population faces a number of health issues like cardiac disorders, skin abrasions, dementia, loss of cognitive functions, renal failure, osteoporosis, etc. All these conditions are the exposition of the biological consequences of old age.(1,2)
Causes of Biological Aging
There is a myriad of factors that cause the senescence or aging of the human body. The reasons for the biological effects of aging are cited as follows:
One of the most significant reasons for our aging is the metabolic function of the body. Theories on aging due to oxidative damage suggest that it is a by-product of the normal metabolism that our body performs throughout life. Mutations do not play any role to set in the string process. The rationale behind oxidative damage is that around 3% of the oxygen consumption by mitochondria gets reduced to reactive oxygen species. The reactive oxygen species comprises hydroxyl radical, superoxide ion, and hydrogen peroxide; all of these induce oxidation and damage in the cell membranes, nucleic acids, and proteins. Thus, oxidative damage is involved in conciliating the lifespan of humans.
Wear and Tear Accompanied By Genetic Instability
Wear and tear is the oldest reason cited to account for the process of normal aging. As the human body grows old, all the small damages accumulated over the years start their manifestation on the body. As a result of which the multitude of point mutation increases and the enzymes encoded by the genes exhibit diminished efficiency. If such point mutations take place in ribosomes, it will lead to the synthesis of numerous faulty proteins. Likewise, if the DNA synthesizing enzymes mutate, the overall rate of mutation in the genes will skyrocket. There are pieces of evidence that have found faulty DNA polymerase in senescent tissues and cells.
Damage of Mitochondrial Genome
Mitochondria is the hub of energy production in the body. It is believed that the mutation rate of mitochondria is ten to twenty times sooner as compared to the nuclear DNA mutation. The consequences of mitochondrial mutation are:
- The shortcoming in the production of energy or ATP
- Increased synthesis of the reactive oxygen species as the electron transport system is impaired
- Apoptosis or cell death induction
The human body witnesses a decline in mitochondrial function with increasing age. A study reveals that the human body has mutation sensitive mitochondrial genomes that are known as hot spots. These hot spots increase the mutation rate of the mitochondria and make them susceptible to damage from reactive oxygen species.
Shortening of Telomeres
Telomeres are the repeated arrangements of DNA present at the tail of the chromosomes. Telomeres are not subjected to normal replication by DNA polymerase. They tend to get short after each cell division. The enzyme called telomerase joins the telomere to the end of the chromosome. It is speculated that the telomeres act as a biological clock that eventually prohibits cell division with age. Thus, contributing to the process of aging by the cessation of somatic cell division.
Programs of Genetic Aging
The effect of genes in premature aging is manifested in the form of diseases and syndromes. One of the most commonly observed genetic aging in children is the Hutchinson Gilford progeria syndrome. In this condition, the children grow old rapidly and usually die due to cardiac failure at an early age of around 12 to 15 years. The genetic mutation of genes in the syndrome includes symptoms like age spots, hair loss, thin transparent skin, reduced bone mass, arteriosclerosis, etc.(3,4)
Biological Changes Due To Aging
Aging is a dynamic physiological function of the human body that sets in with time. The biological envoys that contribute to the process of aging are sedentary lifestyle with reduced physical activity, improper nutrition, the burden of psychomotor functions, chronic as well as acute health disorders, and psychosocial changes in the environment like isolation, loneliness, and lack of care during old age.
The biological effects that are observed in the human body due to aging are as follows:
- Deterioration of tissues and organs which gradually leads to death
- Dehydration of the external and internal cell structures that lead to a decline in the volume of total body fluids. With age, the percentage of total body fluid is reduced from 60% in adulthood to 45% in old age
- The slowdown of metabolic functions results in the deposition of fat cells as well as the withering of tissue muscles(5)
The Biological Effect Of Aging On The Heart
With increasing age, the biological functions of the body, like homeostatic regulation and other cellular events, start to dwindle. The age influenced by the biological effect on the heart is exhibited in the form of Cardio-Vascular Diseases. Old age decreases the efficiency of homeostatic regulation, which in turn damages cardiac tissues and increases death rates. As cellular aging kicks in, there is advanced damage to the cardiac cell and vascular smooth muscle function. Both components are important for maintaining cardiovascular control by virtue of their excitability, contractility, conductivity, and elasticity properties. The common biological effects of aging on the heart are as follows:
- The functional and adaptive capacity of the heart and blood vessels decline
- Left ventricle hypertrophy, fibrosis, and diastolic function sets in leading to low diastolic blood filling and low cardiac output
- The size of cardiac cells increase thereby condensing the wall of the left ventricle and changes the shape of the heart
- Deposition of adipose tissue on the heart cells and calcification of aortic valves leads to atherosclerosis and cardiac failure
- The decline of mitochondrial function with age gives rise to oxidative damage and thus leads to senescence of the heart(6,7)
The Biological Effect Of Ageing On The Brain
The biological effect of aging can be observed in the cognition and various functions of the brain. Old age influences the brain molecules, cells, vasculature, morphology as well as cognitive functions. While approaching senescence, the frontal cortex of the brain shrinks. The research findings state that after the age of 40, the grey matter of the brain starts declining with a rate of 5% every year. It escalates as we cross the age of 70.
Another common biological effect of old age on the brain is the loss of cognitive functions. The most widely noticed cognitive alteration with age is the loss of memory. Episodic memory and semantic memory considered crucial with regard to ageing. It leads to a slow reaction period, reduced attention, the decline in processing speed, deterioration of sensory and perceptive functions, etc. Out of these effects, dementia impacts the older population greatly. There is an exponential surge in cases of dementia, with almost 20% in people above 80 years and around 40% in people above 90 years.(8)
The Biological Effect Of Ageing On Bone And The Nervous System
The biological effect of ageing is expressed on the skeletal and nervous system of the body. Osteoporosis and Senile dementia are the manifestations of old age. The bone mass decreases as the calcium erodes away. The calcium from the bone then sediments in the nervous system. It leads to osteoporosis, which is characterized by weak bones, pain in knees and legs, etc. The prevalence of osteoporosis is high in the female population as compared to the male population. As the level of calcium increases in the brain and peripheral nerves, it leads to chronic renal failure. The high level of calcium in the brain is also found in patients with Alzheimer’s disease. It is one of the reasons that old people are more prone to fall prey to Alzheimer’s disease. The impact on the bone and nervous system is mediated by common factors like deficiency of calcium and Vitamin D, and a shift of calcium content from bones to soft tissues. All these factors lead to osteoporosis and loss of cerebral functions due to old age.(9)
The Biological Effect Of Ageing On The Intestine
Aging is responsible for the breakdown of various biological functions of the body, and one of them is the absorption properties of the intestine. There are many studies indicating that with old age, there are significant changes in intestinal absorption of fatty acids, cholesterol, vitamins, etc. The alteration in intestinal absorptive function is attributed to the increased surface area of the inner layers of the intestine. Previously it was assumed that dietary caloric restriction would help to increase the lifespan by controlling the absorptive permeability of the intestine. But, the studies revealed that lifelong caloric restriction is not able to prevent the change in the intestine with aging. Furthermore, with an increase in age, the barrier function of the intestine withers away and permits the systemic absorption of the lumenal antigens. The condition further leads to other complications like antigen-related disorders with old age.(10)
The Biological Impact Of Aging On The Fertility
Aging renders a negative impact on the biochemical processes of the body and gives rise to the dysfunction of specialized cells and organs. A recent study helps to comprehend the fact that with an increase in age, the quality of the oocytes dwindles. It also reduces the quality of fertility in females. It is the main reason that females who conceive in their later 30s are prone to preterm birth and pregnancy-induced hypertensive disorders. In older women, the oocytes exhibit abnormal chromosome division, inferior mitochondrial characteristics, mitochondrial mutation, high oxidative stress, and low energy production. Women who get pregnant at an older age are more likely to face complications during pregnancy like miscarriage, post-term delivery, premature delivery, the low weight of the child, and cesarean delivery. If the invite fertilization is taken into consideration, the older females have a high risk of failure as compared to the younger females. Thus, old age leads to senescence of reproductive cells as well as organs that can lead to reduced fertility and increased complications in more aged women.(11)
The Biological Effect Of Aging On The Skin
Skin is the foremost part that shows the signs of aging. The main reason is that with old age, the skin loses the elasticity air to the damage of subcutaneous fat deposits. The development of crow’s feet, wrinkles, and sagging are visible on the skin. The skin becomes transparent as the epidermis withers away with age, and skin becomes fragile with thin blood vessels. The signs of aging on the face include loss of cartilage mass from the nose. It leads to the dropping down of the tip and highlights the bony structure of the nose. With age, the skin becomes susceptible to damage by Sundays.(12)
Reversal Of The Biological Effect Of Aging By Dietary Restriction
The early human history has traces of the connection between nutrition and delay in the onset of aging. The ancient literature has promoted the use of food to treat various disorders, but they have also documented that excess dietary intake can lead to early deaths. The use of dietary restriction as an antioxidant treatment against oxidative damage is a phenomenal intervention to reverse the biological effects of aging. The dietary restriction can cease the damage to the DNA as well as other lipids and proteins that contribute towards aging.(13)
Aging leads to the detriment of the metabolism and functions of crucial organs of the body. The causative agents of senescence are gene mutation, damage of cells due to oxidative stress, wear and tear of cells, and mutation of mitochondrial ribosomes. The biological effects of aging are empirical on the cardiovascular system, cognitive functions of the brain, bone density, nervous system, fertility, and dermal layers. The restriction on dietary intake is a promising proposition to cease or reverse the signs of aging.
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