Introduction
Aging is broadly defined as a decrease in the ability to survive. Aged people have less ability to perform strenuous physical activities and show the deteriorating condition of the organs and increased susceptibility to the diseases. Life expectancy is defined as the average length of the life of the individuals in a population. In developed countries, the life expectancy has increased due to the availability of modern medicines, public health care, nutrition and housing.
Aging of cells, tissues, organs and systems
Aging affects cells, tissues, organs and the system in different ways. The efficiency of the cellular functions decreases and the shape of the cell organelles like nuclei and endoplasmic reticulum changes with an increase in age. For example, there is a decline in the synthesis of structural, enzyme and receptor proteins and also in repairing the chromosomal damage.
Effect on tissues is seen in the case of muscle mass that are subjected to muscle atrophy characterized by a reduction in the size of muscle groups and loss of muscle fibers. Arthritis is another such example. All this leads to decreased capacity to work.
With the increase in the age, a decrease in the size and activity of organs can be seen. For example, the elasticity and the size of the lungs are reduced. The weight and volume of the kidneys decrease resulting in reduced filtration rate. Changes also occur in the sense organs. Changes in the brain lead to a decline in the problem-solving and learning ability and also memory impairment.
Changes like wrinkling of the skin, skin pigmentation, graying and loss of hair become quite visible with the age. Skin wounds heal more slowly. Endocrine function and immune function also decline with the age.
Causes of aging
The theories can be divided into two broad categories to explain cellular aging.
Wear and tear theories. These theories suggest that the aging process is due to the exposure to different harmful agents like free radicals, glycated proteins etc. Free radicals are harmful due to the presence of an unpaired electron. They are produced during phagocytosis or during the smoking. Highly reactive hydroxyl radical (OH-) is a free radical that is produced by the action of ionizing radiations in biochemical processes.
Proteins exposed to reducing sugars may undergo glycation. These glycated proteins may further react to form advanced glycation end products (AGEs) that causes increased cross-linking of individual proteins. Thus, the elasticity and permeability of the extracellular matrix is reduced and it also affects the flow of nutrients and waste products. Waste products like lipofuscins accumulate in the cytoplasm with the increasing age. Gradual accumulation of waste products interferes with the normal function of the cells.
Error-catastrophe theory suggests that cellular dysfunction and the cell death occur due to the accumulation of the abnormal proteins. These proteins are formed due to random errors in the transcription and translation. In older cells, certain enzymes have changed the conformation that cannot be repaired with the increase in the age.
Genome based theories. The theory of programmed aging proposes that the aging is genetically programmed. Cells are restricted in the number of times they can enter the cell cycle by senescence and the numbers of divisions are constant for each cell known as the Hayflick limit. The gene mutation theory suggests that the mutations that occur throughout the life in the cell ultimately lead to organ malfunctions and death.
Age related diseases
A number of factors like exposure to harmful agents and increased sensitivity to agents or the environment are responsible for a number of age related diseases such as, cancer, cardiovascular disease, arthritis etc.
The incidence of cancer increases with the age due to the accumulation of the carcinogenic substances or the age-related changes that make the cells more susceptible to cancer. An increase in the concentration of cholesterol increases the chances of cardiovascular diseases. An inappropriate diet, smoking and lack of exercise are associated with atherosclerosis. Diabetes mellitus type 2 is another disease in elderly people that is caused due to the increased resistance to insulin. Arthritis causes inflammation of the joints. Osteoarthritis affects the fingers, hip joints and knees. Elderly people also suffer from Parkinson’s disease where they have severe attacks of tremors that affect one hand and spread to the leg on the same side and to the other limbs.
Calorie restriction and aging
‘Calorie restriction’ is the reduced energy intake that slows down the rate of aging. Thus, the onset of age-related diseases like cancer, cataract and hypertension is delayed. Calorie restriction is associated with a reduction in age-associated mutations. A calorie restricted diet reduces free radical damage to lipids, DNA and proteins.
Investigations and management of the elderly
Many conditions are common in the elderly. For example, renal failure or impaired healing of wounds is observed in elders with diabetes. Further, the elders also have poor nutrition and are on multiple medications. Thus, it is important to carry out the screening of the elders by the clinicians, hospitals and geriatric clinics using different clinical tests.
